Saturday, January 24, 2009
Bad sounding data 12Z 24 Jan 2009
There is a severe superadiabatic layer aloft in this morning’s TWC sounding due to wetbulbing when the wetted sensor moved into a dry layer aloft. This transition was just below 700 mb and the “observed” 700 mb temperature is at least 5C too cold. See figures.
Wednesday, January 21, 2009
Model Comment from Art Douglas
I agree with your comments on the GFS and ECMWF tendencies over the past two years. I would add that in major pattern changes the ECMWF seems to do a better job in capturing that pattern change before the GFS finally switches. It appears now that the deep trof in the East will soon be replaced by a broad ridge in the Southeast. This pattern change is connected to the retrograding ridge in the Northwest that will be replaced by broad troughing along the Pacific Northwest Coast.
Until Sunday, the GFS was the model that was holding on to a very cold East while the ECMWF was starting to show the reversal with the building heights in the Southeast.Then the 12Z GFS on Sunday looked like last night's 0Z GFS run. Both runs had deep closed lows off California and a building ridge in the Southeast third of the country. This morning's new 12Z GFS has a closed low near Point Conception. As you point out the ECMWF has not been leaning this direction with a coastal system............but it suddenly changed last night with a deep trough down the California coast with similar 552 HTS near Point Conception (but not a closed low in any of the ECMWF ensembles). I bet the 12Z ECMWF will have some members with a closed low.
The current 12Z GFS and older 0Z ECMWF both have >0.50" in southeast AZ for the next 5 days and almost 1" on the Rim northwest of Phoenix. So the models are now converging and this time the GFS is the bold model per the pattern change. What happens on the plains is still a crap shoot given how far out it is.
Until Sunday, the GFS was the model that was holding on to a very cold East while the ECMWF was starting to show the reversal with the building heights in the Southeast.Then the 12Z GFS on Sunday looked like last night's 0Z GFS run. Both runs had deep closed lows off California and a building ridge in the Southeast third of the country. This morning's new 12Z GFS has a closed low near Point Conception. As you point out the ECMWF has not been leaning this direction with a coastal system............but it suddenly changed last night with a deep trough down the California coast with similar 552 HTS near Point Conception (but not a closed low in any of the ECMWF ensembles). I bet the 12Z ECMWF will have some members with a closed low.
The current 12Z GFS and older 0Z ECMWF both have >0.50" in southeast AZ for the next 5 days and almost 1" on the Rim northwest of Phoenix. So the models are now converging and this time the GFS is the bold model per the pattern change. What happens on the plains is still a crap shoot given how far out it is.
Performance of the GFS versus the ECMWF
AJ from the NWS has suggested that it might be useful to start a thread on the blog focused on the mid-range performance of the GFS in comparison to that of the ECMWF. So this post is in response to his request.
First, some qualifiers:
I am not a model expert and all of my comments result from subjective appraisal of the various forecasts. I have not attempted to keep any kind of quantitative verifications, and the degree to which I examine the model forecasts at 3 to 7 days depends upon my level of interest and time available. Thus, my inputs are purely informal. I do not have access either to the ECMWF quantitative precipitation forecasts at this time, nor to many of the products from the GFS that are available at NWS offices. I tend to examine products at the NCEP web page and at the PSU electronic wall. I usually examine the 00Z runs, since sometimes the GFS goes into a flip-flop mode where the forecasts are quite different at 12 GMT than at 00Z GMT – I never bother to examine the runs at the 6-hour off times. I usually look most closely at the model forecasts over the Southwest and am thus regionally biased. All of that said, I note the following:
During this winter, and especially last winter, the mid-range ECMWF has seemed to catch important systems, and moisture influxes, better than the GFS. This has been a distinct enough difference that I routinely examine the ECMWF out to 168 hours before I check the GFS forecasts. I have noticed this winter that the GFS operational run is often quite similar to the ECMWF operational run (I don’t have access to, or know where, to examine the ECMWF ensemble members). However, the runs from last night at 00 GMT on January 21, 2009 are VERY different. Thus, today is a good day to try to start a new blog thread.
Note that at 168 hours from last evening (valid time 00 GMT on January 28th) the GFS indicates a quite cold cutoff west of southern California with a distinct 500 mb ridge over western Canada.. The GFS indicates significant precip over much of the West and Southwest and does not indicate precip over the central and northern Plains. On the other hand, the ECMWF indicates the two most important short-waves to be over Colorado and western Canada, with trailing vorticity across southern California into the east Pacific. The ECMWF indicates a frontal like band of precip across the Southwest. But the ECMWF forecasts an intense lee low and strong baroclinic zone over the Plains. Indeed the ECMWF indicates that near blizzard conditions would be impacting the central and high Plains at 168 hours.
I suspect that when the ECMWF performs better than the GFS that it is because its initialization over the Pacific, and also at low latitudes, is capturing features of key importance more accurately. This is sometimes especially noticeable with subtropical features and moisture fields. I think that it is well known that the GFS tends to be too dry over the Southwest.
I have also noticed that if the GFS ensemble members come into sync and consistently forecast precip over southeast Arizona in 10 to 12 of the members, then precip is almost certain to occur. This is true even at low elevations (the 00Z run indicates precip over SE Arizona in only 5 of the 12 members at 168 hours). Note that I have seen a couple of cases during the past two winters where the GFS forecasts were better than those of the ECMWF, but my subjective conclusion remains that I should examine the ECMWF first and then consider and contrast the other models.
What do readers think?
First, some qualifiers:
I am not a model expert and all of my comments result from subjective appraisal of the various forecasts. I have not attempted to keep any kind of quantitative verifications, and the degree to which I examine the model forecasts at 3 to 7 days depends upon my level of interest and time available. Thus, my inputs are purely informal. I do not have access either to the ECMWF quantitative precipitation forecasts at this time, nor to many of the products from the GFS that are available at NWS offices. I tend to examine products at the NCEP web page and at the PSU electronic wall. I usually examine the 00Z runs, since sometimes the GFS goes into a flip-flop mode where the forecasts are quite different at 12 GMT than at 00Z GMT – I never bother to examine the runs at the 6-hour off times. I usually look most closely at the model forecasts over the Southwest and am thus regionally biased. All of that said, I note the following:
During this winter, and especially last winter, the mid-range ECMWF has seemed to catch important systems, and moisture influxes, better than the GFS. This has been a distinct enough difference that I routinely examine the ECMWF out to 168 hours before I check the GFS forecasts. I have noticed this winter that the GFS operational run is often quite similar to the ECMWF operational run (I don’t have access to, or know where, to examine the ECMWF ensemble members). However, the runs from last night at 00 GMT on January 21, 2009 are VERY different. Thus, today is a good day to try to start a new blog thread.
Note that at 168 hours from last evening (valid time 00 GMT on January 28th) the GFS indicates a quite cold cutoff west of southern California with a distinct 500 mb ridge over western Canada.. The GFS indicates significant precip over much of the West and Southwest and does not indicate precip over the central and northern Plains. On the other hand, the ECMWF indicates the two most important short-waves to be over Colorado and western Canada, with trailing vorticity across southern California into the east Pacific. The ECMWF indicates a frontal like band of precip across the Southwest. But the ECMWF forecasts an intense lee low and strong baroclinic zone over the Plains. Indeed the ECMWF indicates that near blizzard conditions would be impacting the central and high Plains at 168 hours.
I suspect that when the ECMWF performs better than the GFS that it is because its initialization over the Pacific, and also at low latitudes, is capturing features of key importance more accurately. This is sometimes especially noticeable with subtropical features and moisture fields. I think that it is well known that the GFS tends to be too dry over the Southwest.
I have also noticed that if the GFS ensemble members come into sync and consistently forecast precip over southeast Arizona in 10 to 12 of the members, then precip is almost certain to occur. This is true even at low elevations (the 00Z run indicates precip over SE Arizona in only 5 of the 12 members at 168 hours). Note that I have seen a couple of cases during the past two winters where the GFS forecasts were better than those of the ECMWF, but my subjective conclusion remains that I should examine the ECMWF first and then consider and contrast the other models.
What do readers think?
Sunday, January 11, 2009
Happy New Year !
The blog has been a bit quiet lately, but we do have some news:
MADWEATHER has been listed as one of the 100 Best Blogs for Earth Science Scholars !!
See: http://www.bachelorsdegreeonline.com/blog/2008/100-best-blogs-for-earth-science-scholars/
Thanks to all of our blog readers and contributors!
The blog has been a bit quiet lately, but we do have some news:
MADWEATHER has been listed as one of the 100 Best Blogs for Earth Science Scholars !!
See: http://www.bachelorsdegreeonline.com/blog/2008/100-best-blogs-for-earth-science-scholars/
Thanks to all of our blog readers and contributors!
Saturday, October 25, 2008
Continuing Problems with RRS Data
All,
FYI - I have posted an article
"Strongly Superadiabatic Lapse Rates Aloft at Six Upper-Air Sounding Sites"
coauthored with Barry Schwartz at:
http://www.madweather.com/
We have examined data for two years of RRS soundings and compared with data from earlier sondes. This quantitative comparison indicates a very serious decline in the quality of the upper-air data is occurring because of the use of the new Sippican GPS microsondes by the NWS.
FYI - I have posted an article
"Strongly Superadiabatic Lapse Rates Aloft at Six Upper-Air Sounding Sites"
coauthored with Barry Schwartz at:
http://www.madweather.com/
We have examined data for two years of RRS soundings and compared with data from earlier sondes. This quantitative comparison indicates a very serious decline in the quality of the upper-air data is occurring because of the use of the new Sippican GPS microsondes by the NWS.
Thursday, August 21, 2008
Response to AJ-NWS
Response to AJ of NWS - see AJ's comment on the previous post.
AJ makes a very good point here and one that serves to emphasize how difficult the forecast challenge is for the coming 84 hours. The three principal models each have different solutions, and we have little in the way of observational data to help evaluate the model initializations, since the key features analyzed by the models are within a great data void.
First, if one looks at the NAM, the GFS, and the ECMWF model runs from this morning – which I hadn’t when I wrote the original blurb – it is clear that each of the three models has somewhat different solutions for the initial conditions.
As per at 500mb:
The GFS analyzes an IT from south of GoC into north central MX where it connects with a trailing trough from the S/W over the central Missouri River Basin.
The ECMWF has this feature analyzed further north, extending from the south central GoC to SE Kansas.
The NAM is similar to the ECMWF except that it has several additional vorticity maxima further south and southeast which neither of the global models have.
We do know that such a feature is present and that at 12Z this morning it extended from Nebraska south-southwestward entering Mexico in the western Big Bend country.
Each model goes it own way in the forecast fields. The most important issue relates to whether or not there is a feature in the actual atmosphere that is going to spinup into a tropical system off Baja. Only the NAM indicates this evolution. The NAM solution would result in a very deep intrusion of subtropical moisture into the Southwest. At this time we mostly know that there has been ongoing convection in the regions where the NAM forecasts tropical development.
Both the GFS and ECMWF strengthen the inverted trough over north central Mexico and forecast this as the main feature that affects southern Arizona on Saturday and Sunday. The GFS stalls this feature over north central Mexico, while the ECMWF is more aggressive and keeps it further north and moving westward. The wind shear profile forecast on Sunday by the GFS is not nearly as favorable for organized storms (assuming that the key ingredients of moisture and CAPE have moved/developed north of the border). The ECMWF is probably in between the two other models wrt wind shear.
Current IR and water vapor satellite imagery indicate that the feature over north central Mexico has a clear circulation now and that it is moving westward. Significant convection is developing ahead of this feature over the Sierra Madre Occidental.
So where does all this lead? The forecast situation appears even more complicated than what I originally wrote. The most likely scenario for the next 84 hours is not at all clear at this time, and the evolving situation merits careful monitoring.
AJ makes a very good point here and one that serves to emphasize how difficult the forecast challenge is for the coming 84 hours. The three principal models each have different solutions, and we have little in the way of observational data to help evaluate the model initializations, since the key features analyzed by the models are within a great data void.
First, if one looks at the NAM, the GFS, and the ECMWF model runs from this morning – which I hadn’t when I wrote the original blurb – it is clear that each of the three models has somewhat different solutions for the initial conditions.
As per at 500mb:
The GFS analyzes an IT from south of GoC into north central MX where it connects with a trailing trough from the S/W over the central Missouri River Basin.
The ECMWF has this feature analyzed further north, extending from the south central GoC to SE Kansas.
The NAM is similar to the ECMWF except that it has several additional vorticity maxima further south and southeast which neither of the global models have.
We do know that such a feature is present and that at 12Z this morning it extended from Nebraska south-southwestward entering Mexico in the western Big Bend country.
Each model goes it own way in the forecast fields. The most important issue relates to whether or not there is a feature in the actual atmosphere that is going to spinup into a tropical system off Baja. Only the NAM indicates this evolution. The NAM solution would result in a very deep intrusion of subtropical moisture into the Southwest. At this time we mostly know that there has been ongoing convection in the regions where the NAM forecasts tropical development.
Both the GFS and ECMWF strengthen the inverted trough over north central Mexico and forecast this as the main feature that affects southern Arizona on Saturday and Sunday. The GFS stalls this feature over north central Mexico, while the ECMWF is more aggressive and keeps it further north and moving westward. The wind shear profile forecast on Sunday by the GFS is not nearly as favorable for organized storms (assuming that the key ingredients of moisture and CAPE have moved/developed north of the border). The ECMWF is probably in between the two other models wrt wind shear.
Current IR and water vapor satellite imagery indicate that the feature over north central Mexico has a clear circulation now and that it is moving westward. Significant convection is developing ahead of this feature over the Sierra Madre Occidental.
So where does all this lead? The forecast situation appears even more complicated than what I originally wrote. The most likely scenario for the next 84 hours is not at all clear at this time, and the evolving situation merits careful monitoring.
Challenging Forecast for the Weekend - Aug 23 and 24 2008
It appears that the large-scale setting here in the Southwest will be changing rapidly during the coming three days as very warm air in middle levels pushes into the Great Basin. Note the very warm 500 mb temperatures of only -4C at Medford OR and -3C at Desert Rock NV this morning. This warm intrusion builds the anticyclone back to our north and helps setup a more typical late summer flow regime.
Pressures have fallen and are quite low over the interior Southwest and may drop another couple of mb over the next 36 hours. There is also a weak inverted trough over the lower end of the GoC that has widespread convection associated with it. As this first disturbance shifts westward, there should be a low-level surge of moisture back into the lower Colorado River Basin. This moisture surge could begin as early as morning tomorrow but should be quite pronounced by mid-day Saturday.
The NAM forecasts that a tropical storm will develop just southwest of the tip of Baja and this feature, if it materializes, would deepen the moisture inflow to Arizona on Sunday and Monday. The NAM also forecasts very favorable wind shear profiles for organized convective storms in southeastern AZ both on Saturday and Sunday afternoons. Thus, both days could be very active if there is CAPE available.
It appears that the crucial aspect of the weekend synoptic setting will the temperatures in the middle levels. If the very warm air to the north and northwest spreads over southern Arizona and northern Mexico there would be little CAPE to realize, and it would likely be fighting an inversion aloft. However, if the easterly flow that develops at 500 mb has a fetch from the central and southern Plains by Saturday afternoon, the 500 mb temperatures would be much cooler and supportive of storms.
I think that the more favorable situation will evolve and, depending on the details, either Saturday or Sunday afternoon and evening should be quite active with strong and organized storms.
Pressures have fallen and are quite low over the interior Southwest and may drop another couple of mb over the next 36 hours. There is also a weak inverted trough over the lower end of the GoC that has widespread convection associated with it. As this first disturbance shifts westward, there should be a low-level surge of moisture back into the lower Colorado River Basin. This moisture surge could begin as early as morning tomorrow but should be quite pronounced by mid-day Saturday.
The NAM forecasts that a tropical storm will develop just southwest of the tip of Baja and this feature, if it materializes, would deepen the moisture inflow to Arizona on Sunday and Monday. The NAM also forecasts very favorable wind shear profiles for organized convective storms in southeastern AZ both on Saturday and Sunday afternoons. Thus, both days could be very active if there is CAPE available.
It appears that the crucial aspect of the weekend synoptic setting will the temperatures in the middle levels. If the very warm air to the north and northwest spreads over southern Arizona and northern Mexico there would be little CAPE to realize, and it would likely be fighting an inversion aloft. However, if the easterly flow that develops at 500 mb has a fetch from the central and southern Plains by Saturday afternoon, the 500 mb temperatures would be much cooler and supportive of storms.
I think that the more favorable situation will evolve and, depending on the details, either Saturday or Sunday afternoon and evening should be quite active with strong and organized storms.
Saturday, August 16, 2008
Slide shows re Severe Storm of 13 August 2008
Still bringing the new PC online, so none of the photos I took of damage produced by the early nigttime storm of Wednesday August 13th have been posted in the gallery. However, each of the Tucson newspapers have slide shows attached to their online articles about the storm.
http://www.azstarnet.com/sn/hourlyupdate/252838.php
http://www.tucsoncitizen.com/ss/local/93782.php
http://www.azstarnet.com/sn/hourlyupdate/252838.php
http://www.tucsoncitizen.com/ss/local/93782.php
Thursday, August 07, 2008
Computer Problems
I have been struggling with a failing PC here at the house and have been just able to get online every once in awhile. Thus, everything I usually do is to some extent on hold. We are going to replace this PC, but I may be out of touch for much of the next week or two, until a new computer is up and functional here. Bob
"When it rains it usually pours, but sometimes it just spits."
Rex Block
Private Investigator
Forensic Meteorologist
"When it rains it usually pours, but sometimes it just spits."
Rex Block
Private Investigator
Forensic Meteorologist
Sunday, August 03, 2008
Sunday Morning Postmortem
Well my guess for yesterday afternoon was about as bad as I can do. Obviously the negatives dominated the local area around Tucson - only 7 of the 91 Alert gauges had rain yesterday, and the highest amount was 0.59 way down south at Tubac.
So what went wrong - I think that it was mainly related to the dry air in the upper-troposphere curling across southeast Arizona and keeping there from being much activity to the east - as per the WRF forecast. Although there were more storms to the east than the WRF indicated, they were not widespread and didn't produce any significant, organized outflows. With the GoC surge and increasing low-level moisture, the Tucson sounding at 00Z yesterday afternoon had substantial CAPE, but needed mesoscale convergence to kick it loose. That didn't happen.
As for today - moisture is way up as expected and there is substantial CAPE at both TUS and PHX this morning. El Paso is fairly stable so we have to assume that the air over the southeastern mountains is somewhat like the Tucson sounding. Morning wind shear from middle to upper levels is unidirectional but the NAM indicates that the wind profiles may improve by evening. Mainly a shear zone affecting southeast Arizona today and with no data from the south, it is hard to have much confidence in the model predicted winds aloft. So, there will be a lot of small and mesoscale interactions driving the evolution of storms today - good potential for more severe across all of southern Arizona and Phoenix could get hit by a strong, severe storm event. The chances are probably better for here at house today, but, even though it's not a binary call like yesterday, the shear profile could throw anvils over this part of town. So it's wait and see, as per many to most storm days down here.
The other wild card at play here is that there is a lot of strong morning storm activity out to the west of Tucson. If these storms continue to build produce early, cool outflows, that would complicate things greatly. I got a couple photos as sunrise showers moved by, producing an early morning rainbow. I'll post these to the blog later today.
So what went wrong - I think that it was mainly related to the dry air in the upper-troposphere curling across southeast Arizona and keeping there from being much activity to the east - as per the WRF forecast. Although there were more storms to the east than the WRF indicated, they were not widespread and didn't produce any significant, organized outflows. With the GoC surge and increasing low-level moisture, the Tucson sounding at 00Z yesterday afternoon had substantial CAPE, but needed mesoscale convergence to kick it loose. That didn't happen.
As for today - moisture is way up as expected and there is substantial CAPE at both TUS and PHX this morning. El Paso is fairly stable so we have to assume that the air over the southeastern mountains is somewhat like the Tucson sounding. Morning wind shear from middle to upper levels is unidirectional but the NAM indicates that the wind profiles may improve by evening. Mainly a shear zone affecting southeast Arizona today and with no data from the south, it is hard to have much confidence in the model predicted winds aloft. So, there will be a lot of small and mesoscale interactions driving the evolution of storms today - good potential for more severe across all of southern Arizona and Phoenix could get hit by a strong, severe storm event. The chances are probably better for here at house today, but, even though it's not a binary call like yesterday, the shear profile could throw anvils over this part of town. So it's wait and see, as per many to most storm days down here.
The other wild card at play here is that there is a lot of strong morning storm activity out to the west of Tucson. If these storms continue to build produce early, cool outflows, that would complicate things greatly. I got a couple photos as sunrise showers moved by, producing an early morning rainbow. I'll post these to the blog later today.
Saturday, August 02, 2008
Storm Outlook for Today
Visually spectacular storms yesterday evening - if anyone has photos for pasting on the blog, let me know.
Hot boundary layer temps and pocket of cooler 500 mb air, plus slight increase in moisture allowed storms, particularly at higher elevations, to overcome the strong inversion near 400 mb. Rain reported at 23 of the 91 Alert gauges in eastern Pima County - again mostly in mountains and foothills - the 1.50" at Agua Calienta Park seems an outlier, but there was spectacular lightning off that way. One wind damage report out at Pinal Airpark. Afternoon cells did not seem to have much in the way of precip shafts but then things obviously changed before dark.
Here at house - lightning, thunder and brief spit of rain shortly after 9 pm.
Situation today is very difficult with a number of competing plus and minuses.
Negatives first:
Very dry air to east in NM
Morning soundings continue with marginal IPW and boundary layer moisture.
Best difluence ahead of approaching upper-level, inverted trough appears to remain south of border.
Upper-level winds weak as we remain near the center of upper anticyclone.
Cool pocket at 500 mb has moved on to our west and northwest.
Pluses:
Nice push of subtropical moisture occurring into lower Colorado Basin, with some signature in PHX am sounding and Yuma VAD showing the influx to be about 4,000 ft deep. GPS IPW shows nice increases at the stations around the northern GoC.
Outflows from MCS over Mexico last night have pushed Td up across all of southern AZ and helped the GoC surge along.
Tropical low spinning off Baja in good location to keep low-level moisture flow going for a couple of days.
Very nice steering winds for storms that will tend to leave anvils to rear of strong cells.
Approaching inverted trough that extends down to 700 mb.
Summary - Looks good for strong storms with likely tropical squall line organization and somesevere storms and heavier rains, but today or tomorrow? I think things will come together today better than one might expect and that afternoon and evening should have strong storms - tomorrow will of course be highly affected by what does or does not happen during the next 12 hours. Chance of rain here at house probably at least 50% this evening.
Hot boundary layer temps and pocket of cooler 500 mb air, plus slight increase in moisture allowed storms, particularly at higher elevations, to overcome the strong inversion near 400 mb. Rain reported at 23 of the 91 Alert gauges in eastern Pima County - again mostly in mountains and foothills - the 1.50" at Agua Calienta Park seems an outlier, but there was spectacular lightning off that way. One wind damage report out at Pinal Airpark. Afternoon cells did not seem to have much in the way of precip shafts but then things obviously changed before dark.
Here at house - lightning, thunder and brief spit of rain shortly after 9 pm.
Situation today is very difficult with a number of competing plus and minuses.
Negatives first:
Very dry air to east in NM
Morning soundings continue with marginal IPW and boundary layer moisture.
Best difluence ahead of approaching upper-level, inverted trough appears to remain south of border.
Upper-level winds weak as we remain near the center of upper anticyclone.
Cool pocket at 500 mb has moved on to our west and northwest.
Pluses:
Nice push of subtropical moisture occurring into lower Colorado Basin, with some signature in PHX am sounding and Yuma VAD showing the influx to be about 4,000 ft deep. GPS IPW shows nice increases at the stations around the northern GoC.
Outflows from MCS over Mexico last night have pushed Td up across all of southern AZ and helped the GoC surge along.
Tropical low spinning off Baja in good location to keep low-level moisture flow going for a couple of days.
Very nice steering winds for storms that will tend to leave anvils to rear of strong cells.
Approaching inverted trough that extends down to 700 mb.
Summary - Looks good for strong storms with likely tropical squall line organization and somesevere storms and heavier rains, but today or tomorrow? I think things will come together today better than one might expect and that afternoon and evening should have strong storms - tomorrow will of course be highly affected by what does or does not happen during the next 12 hours. Chance of rain here at house probably at least 50% this evening.
Friday, August 01, 2008
Art Douglas Photos
Art has sent some digital photos from southeast Arizona - four of these have been posted on the Blog Gallery of weather images at www.madweather.com
Art's photos can be viewed directly at
http://www.squidinkbooks.com/madweather/photos-art-douglas.htm
Art's photos can be viewed directly at
http://www.squidinkbooks.com/madweather/photos-art-douglas.htm
Thursday, July 31, 2008
Today's Weather - Southeast Arizona
Have been off-line for last two days due to dsl problems. So, it was the nice cool mornings that told me I shouldn't have doubted the NWS models and forecasts in keeping a dryout over Arizona for most of this week.
This morning there are, however, some indications of changes underway that will bring storms back into this part of the state. This morning there were quite a few ACC drifting around beneath the cirrus at sunrise. Since there has been no NWS sounding taken at TWC the last two sounding times, I have to guess about what a sounding here would look like this morning. There does appear to be some increase in east-northeasterly winds around 500 mb, along with some cooler temps advecting over southeastern Arizona today. Deep, subtropical moisture remains south of Hermosilla, but hot surface temps, along with the cooler middle level temps indicate that high-based storms should return to some of the sky island mountains of southeast Arizona late today, producing some lightning and gusty outflows.
The widespread convective activity over the southern half of GoC, coupled with falling pressures in the lower Colorado Basin, as well as the 500 mb wave moving slowly westward across the lower GoC all are good indicators that a northward push of the subtropical air is imminent. My guess is that we should see a push of low-level moisture into southwest and south central Arizona within 24 to 48 hours, followed by increasing storm activity for the next few days.
This morning there are, however, some indications of changes underway that will bring storms back into this part of the state. This morning there were quite a few ACC drifting around beneath the cirrus at sunrise. Since there has been no NWS sounding taken at TWC the last two sounding times, I have to guess about what a sounding here would look like this morning. There does appear to be some increase in east-northeasterly winds around 500 mb, along with some cooler temps advecting over southeastern Arizona today. Deep, subtropical moisture remains south of Hermosilla, but hot surface temps, along with the cooler middle level temps indicate that high-based storms should return to some of the sky island mountains of southeast Arizona late today, producing some lightning and gusty outflows.
The widespread convective activity over the southern half of GoC, coupled with falling pressures in the lower Colorado Basin, as well as the 500 mb wave moving slowly westward across the lower GoC all are good indicators that a northward push of the subtropical air is imminent. My guess is that we should see a push of low-level moisture into southwest and south central Arizona within 24 to 48 hours, followed by increasing storm activity for the next few days.
Monday, July 28, 2008
MORE BAD SOUNDING DATA AT TUCSON
I have just been perusing the morning sounding data and find that the TWC 1200Z sounding for today - Monday 28 July 2008 - poses a very substantial forecasting dilemma.
The sounding indicates IPW of 1.65" and the SPC analysis of this sounding indicates a forecast CAPE this afternoon of 1180 J/Kg. However, the GPS IPW from FSL indicates that precipitable water is probably between 1.3 to 1.4" - the difference between the sounding value and the GPS value being more than 0.25" - a huge difference and one that could seriously affect the convective forecast. See:
http://www.rap.ucar.edu/weather/upper/twc.gif
Note that the Td increases substantially between the surface value and the first level of sonde data - this aspect of the TWC soundings has been noted off and on - particularly on calm mornings - for the past several weeks. The Td values from the sonde then decrease nearly linearly to 715 mb, even though the sonde was passing through two elevated, residual boundary layers. The Td trace does not appear to be physically realistic and is probably too wet in each of the residual layers. Thus, I conclude that the Td data are bad and that the atmospere's dewpoint structure is quite different than that measured by the RRS sonde.
The reasons for the questionable data are not clear - but two possibilities come to mind - 1) local conditions on the roof of the NWS building may be affecting the first couple of data points and 2) the RRS sonde humidity sensor for this flight had a slow response time for Td and did not properly respond to Td changes below about 715 mb.
So, one is left wondering exactly what the local conditions might actually have been at the time of the sounding. So it goes.
The sounding indicates IPW of 1.65" and the SPC analysis of this sounding indicates a forecast CAPE this afternoon of 1180 J/Kg. However, the GPS IPW from FSL indicates that precipitable water is probably between 1.3 to 1.4" - the difference between the sounding value and the GPS value being more than 0.25" - a huge difference and one that could seriously affect the convective forecast. See:
http://www.rap.ucar.edu/weather/upper/twc.gif
Note that the Td increases substantially between the surface value and the first level of sonde data - this aspect of the TWC soundings has been noted off and on - particularly on calm mornings - for the past several weeks. The Td values from the sonde then decrease nearly linearly to 715 mb, even though the sonde was passing through two elevated, residual boundary layers. The Td trace does not appear to be physically realistic and is probably too wet in each of the residual layers. Thus, I conclude that the Td data are bad and that the atmospere's dewpoint structure is quite different than that measured by the RRS sonde.
The reasons for the questionable data are not clear - but two possibilities come to mind - 1) local conditions on the roof of the NWS building may be affecting the first couple of data points and 2) the RRS sonde humidity sensor for this flight had a slow response time for Td and did not properly respond to Td changes below about 715 mb.
So, one is left wondering exactly what the local conditions might actually have been at the time of the sounding. So it goes.
Thursday, July 24, 2008
Bad RRS Sonde Data Complicate Today's Forecast
Difficult forecast for today.
Low-level moisture has been sloshing around in different ways last night and this early morning, with decreases in the southeast from the east; increases in south central Arizona from the southeast; and increases in lower Colorado Basin due to weak surge which should continue and increase in strength and depth. Diurnal wind regime may return today in the Tucson area, which would increase the low-level moisture.
Entire forecast problem is acerbated by the TWC sounding which is apparently about 7.5 mm too wet this morning. I am guessing the bad data are at and below 850 mb and modifying the sounding accordingly. My estimated sounding for this afternoon has boundary layer well-mixed moisture at 10 g/kg and cloud bases at 650 mb. This gives moderate CAPE with only slight CIN above, assuming no further drying from east.
At 500 mb a weak inverted trof extends from the north end of GoC to SE Colorado, with some cooler air on the east side of this feature. At 200 mb a strong inverted trof extends from west of Albuquerque, south between El Paso and Tucson and into the vast Mexican data void. This setup gives the Tucson area good steering level flow this late afternoon, but little vertical shear. If storms organize along outflows, they could move westward faster than their anvils.
NAM model indicates better wind profiles tomorrow. Thus, good potential for organized and some severe storms either this afternoon or tomorrow, with the answer hiding in the devilish, smaller-scale details.
Low-level moisture has been sloshing around in different ways last night and this early morning, with decreases in the southeast from the east; increases in south central Arizona from the southeast; and increases in lower Colorado Basin due to weak surge which should continue and increase in strength and depth. Diurnal wind regime may return today in the Tucson area, which would increase the low-level moisture.
Entire forecast problem is acerbated by the TWC sounding which is apparently about 7.5 mm too wet this morning. I am guessing the bad data are at and below 850 mb and modifying the sounding accordingly. My estimated sounding for this afternoon has boundary layer well-mixed moisture at 10 g/kg and cloud bases at 650 mb. This gives moderate CAPE with only slight CIN above, assuming no further drying from east.
At 500 mb a weak inverted trof extends from the north end of GoC to SE Colorado, with some cooler air on the east side of this feature. At 200 mb a strong inverted trof extends from west of Albuquerque, south between El Paso and Tucson and into the vast Mexican data void. This setup gives the Tucson area good steering level flow this late afternoon, but little vertical shear. If storms organize along outflows, they could move westward faster than their anvils.
NAM model indicates better wind profiles tomorrow. Thus, good potential for organized and some severe storms either this afternoon or tomorrow, with the answer hiding in the devilish, smaller-scale details.
Tuesday, July 22, 2008
Severe weather pattern setting up last three days of week
Note that we've posted a weekend summary and some recent photos on the madweather web page, with links posted on the blog this morning.
Conditions remain very moist this morning; however, the TWC sounding is about 5mm too high in IPW according to the FSL comparison site. The 12Z sounding is quite strange, exhibiting the off-the-surface moist spike that Mike Leuthold pointed out about a week ago. Many of the 12Z soundings for last several weeks show this same artifact - particularly on calm mornings. This morning's sounding exhibits an adiabatic layer off the surface and then a sharp inversion to about 890 mb. This same layer has the strange Td structures. These data in lowest levels probably reflect the local conditions on the roof of the NWS building, and the moisture spike may result from similar contamination.
Regardless, moist and unstable and a calm troposphere again this morning. Only 11 of the Pima County Alert gauges had precip yesterday - making it the driest day since last Friday - with the significant amounts being on the mountains. The amount of anvil that the early mountain storms produced was truly amazing, but of course left all the lower elevations under thick anvil for much of the afternoon. Looks like anvils will tend to spread toward south and southwest today also.
Upper-level difluence increases this afternoon and evening as the inverted upper trof approaches. This feature directly affects southeastern Arizona tomorrow afternoon and steering level winds finally pick up. The 500 mb temperatures with this feature are -8 to -9C, i.e., very much cooler than have been observed at TWC for many days!
The best vertical shear for organized, propagating MCSs is forecast by the NAM on Thursday afternoon/evening as the winds at high levels - 200 mb - turn to south-southwest as remnants of Dolly approach the Big Bend. Wind shear predicted by the NAM remains very favorable on Friday afternoon. Very difficult to call which day will bring the most intense storms to southeast Arizona for rest of week, since local and small scale features and the previous day's events will be playing a big role each day. But it will be very interesting to observe what actually evolves.
Conditions remain very moist this morning; however, the TWC sounding is about 5mm too high in IPW according to the FSL comparison site. The 12Z sounding is quite strange, exhibiting the off-the-surface moist spike that Mike Leuthold pointed out about a week ago. Many of the 12Z soundings for last several weeks show this same artifact - particularly on calm mornings. This morning's sounding exhibits an adiabatic layer off the surface and then a sharp inversion to about 890 mb. This same layer has the strange Td structures. These data in lowest levels probably reflect the local conditions on the roof of the NWS building, and the moisture spike may result from similar contamination.
Regardless, moist and unstable and a calm troposphere again this morning. Only 11 of the Pima County Alert gauges had precip yesterday - making it the driest day since last Friday - with the significant amounts being on the mountains. The amount of anvil that the early mountain storms produced was truly amazing, but of course left all the lower elevations under thick anvil for much of the afternoon. Looks like anvils will tend to spread toward south and southwest today also.
Upper-level difluence increases this afternoon and evening as the inverted upper trof approaches. This feature directly affects southeastern Arizona tomorrow afternoon and steering level winds finally pick up. The 500 mb temperatures with this feature are -8 to -9C, i.e., very much cooler than have been observed at TWC for many days!
The best vertical shear for organized, propagating MCSs is forecast by the NAM on Thursday afternoon/evening as the winds at high levels - 200 mb - turn to south-southwest as remnants of Dolly approach the Big Bend. Wind shear predicted by the NAM remains very favorable on Friday afternoon. Very difficult to call which day will bring the most intense storms to southeast Arizona for rest of week, since local and small scale features and the previous day's events will be playing a big role each day. But it will be very interesting to observe what actually evolves.
Weather Summary for Past Weekend
We've posted a summary of the weather observed over this past weekend directly on the web page.
http://www.madweather.com/
It can be found under BLOG IMAGE GALLERY Weather Summary for July 18-20
We've also added some other July storm photos here, including lightning photos from near El Paso. these were provided by Mike Hardiman.
http://www.madweather.com/
It can be found under BLOG IMAGE GALLERY Weather Summary for July 18-20
We've also added some other July storm photos here, including lightning photos from near El Paso. these were provided by Mike Hardiman.
Monday, July 21, 2008
Weather Summary Last Three Days - July 18 through 20
Or - this is a direct link to the summary and photos.
Madweather post: Weather Summary Last Three Days - July 18 through 20
Madweather post: Weather Summary Last Three Days - July 18 through 20
CURRENT WEATHER, MONDAY JULY 21, 2008
This morning conditions over most of Arizona remain very moist and the TWC morning sounding (Fig. 1 - link below) indicates a subtropical air mass with just over 50 mm of IPW. Although there is abundant CAPE, the winds aloft are light and variable through most of the troposphere. Thus, the situation is much like yesterday when there were many storms which remained mostly over higher elevations. The large subtropical anticyclone at 500 mb has three distinct sub-centers. The main one is over Arkansas with weaker centers in the west over southeastern Arizona and southwestern Wyoming (see Fig. 2).
The most interesting aspects of this morning's charts and the model forecasts relate to what will occur on Wednesday through Friday. There is a strong upper-tropospheric shear zone at 200 mb from somewhere near the southern end of the Gulf of California that extends east-northeast through the Mexican data void, and then across southeast Texas and southern Arkansas. The NAM initializes this feature a bit to the north and weaker than it appears to be. The NAM forecasts the west end of this feature to become a distinct upper-cyclone that moves westward across northern Mexico on Wednesday and Thursday. As this occurs, the 500 mb steering flow becomes east-northeast. The flow at 200 mb becomes more diffluent, initially from the east-northeast on Wednesday and then from the southeast on Thursday. Thus, a more favorable shear profile returns for propagating and organized storms.
It then appears that the remnants of TS/Hurricane Dolly (see Fig. 3) will affect southern Arizona on Friday and perhaps Saturday. Currently, the models and NHC forecast Dolly to follow a track similar to that of Claudette during the period July 8-17th in 2003. All-in-all it should be an interesting weather week.
Monday, July 07, 2008
Weather Summary - 30 June Through this Morning
The last seven days have been quite amazing here in southeastern Arizona. There have been thunderstorms somewhere in the Tucson metro area every day except for the 30th, which was suppressed due to strong, downslope east winds.
Yesterday was the day with the most widespread rains. A large are of heavy cloud at sunrise acted to suppress local storm development. But shortly after dark outflow winds converged over Tucson, helped by two weak short waves - one from the southeast and one from the northwest - triggering a large MCS. Every one of the Flood Districts 91 gauges reported measurable rainfall except for three - which I suspect may be out of order. Largest accumulation was 2.60 at White Tail on the Catalinas. Here at the house we had 0.60".
Today the two middle-level waves continue to interact and the atmosphere is very wet with high IPW amounts. The widespread rains will mean a shallow boundary layer later today that will need strong outflows into lower elevations if storms are to develop away from the mountains. The longer range forecasts continue with very wet forecasts out past 7 days as both depression Five-E and an upper cyclone over eastern Mexico move slowly this way and continue the flow of subtropical moisture into the Southwest US.
Some summaries for the past seven days:
Douglas Tstms on the 1st, 3rd, 5th, and 6th total rainfall 0.17"
Art Douglas reports storms and rain at Ash Canyon (just south of Sierra Vista)
on the 2nd through the 5th (and probably yesterday also) with rainfall of 1.00"
Nogales: Tstms every day with total rainfall 1.31"
Tucson (TUS) Tstms on 1st, 3rd, 4th, 5th, and 6th total rainfall 0.45"
Here at house Tstms on 1st, 3rd, 4th, 5th, and 6th total rainfall 1.39"
Phoenix (PHX) Tstms on the 3rd and 4th total rainfall only a Trace
Note that Phoenix has had high temps of over 105F every day of this period and that 3 days were over 110F. While temps were over 100F in the afternoons the dewpoints were often in the middle 50s to low 60s. Thus, the heat stress and misery gradient between Tucson and Phoenix this last week has been very strong, probably maximizing between Picacho Peak and Casa Grande.
Yesterday was the day with the most widespread rains. A large are of heavy cloud at sunrise acted to suppress local storm development. But shortly after dark outflow winds converged over Tucson, helped by two weak short waves - one from the southeast and one from the northwest - triggering a large MCS. Every one of the Flood Districts 91 gauges reported measurable rainfall except for three - which I suspect may be out of order. Largest accumulation was 2.60 at White Tail on the Catalinas. Here at the house we had 0.60".
Today the two middle-level waves continue to interact and the atmosphere is very wet with high IPW amounts. The widespread rains will mean a shallow boundary layer later today that will need strong outflows into lower elevations if storms are to develop away from the mountains. The longer range forecasts continue with very wet forecasts out past 7 days as both depression Five-E and an upper cyclone over eastern Mexico move slowly this way and continue the flow of subtropical moisture into the Southwest US.
Some summaries for the past seven days:
Douglas Tstms on the 1st, 3rd, 5th, and 6th total rainfall 0.17"
Art Douglas reports storms and rain at Ash Canyon (just south of Sierra Vista)
on the 2nd through the 5th (and probably yesterday also) with rainfall of 1.00"
Nogales: Tstms every day with total rainfall 1.31"
Tucson (TUS) Tstms on 1st, 3rd, 4th, 5th, and 6th total rainfall 0.45"
Here at house Tstms on 1st, 3rd, 4th, 5th, and 6th total rainfall 1.39"
Phoenix (PHX) Tstms on the 3rd and 4th total rainfall only a Trace
Note that Phoenix has had high temps of over 105F every day of this period and that 3 days were over 110F. While temps were over 100F in the afternoons the dewpoints were often in the middle 50s to low 60s. Thus, the heat stress and misery gradient between Tucson and Phoenix this last week has been very strong, probably maximizing between Picacho Peak and Casa Grande.
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