Sunday, July 22, 2018

Isolated Storms Again Today


Webcam view of the beach at Aberdeen, Scotland, early this afternoon. The British Open is underway right now at Carnoustie, south-southwest of Aberdeen (from Jack Hales cam wall). 



There were isolated thunderstorms yesterday afternoon in southwest Cochise County (near or overhead at Art Douglas' place) and northern Sonora. Graphic above shows detected CG flashes for 24-hours ending at 3:00 am MST this morning - from Atmo and Vaisala).


Graphic above shows the MIMIC layer PW for 13 UTC between 850 and 700 mb - max amounts continue over southeastern Arizona and a repeat is likely today with storms at higher elevations Cochise and Santa Cruz Counties.

Longer term very grim as intense 500 mb anticyclone shifts from northeastern New Mexico to nearly overhead by midweek. The GFS 500 mb forecast below (from 06 UTC run last night) is valid at noon on Wednesday the 22nd.

Saturday, July 21, 2018

Large, Nocturnal MCS July 20-21st


A large MCS developed over the southeast Arizona Borderlands last evening - as forecast by the WRF model runs yesterday morning. The system moved slowly across much of southern Arizona during the night, with two spun-up, mesoscale convective vortices apparent in satellite imagery this morning. The IR image of system above is from 4:30 am MST, while the Yuma composite radar display below is from 6:50 am.



Here in Tucson the MCS produced a nice lightning show after midnight - above (from Atmo and Vaisala) shows detected CG flashes for 24-hours ending at 7:00 am this morning. Note that in eastern Pima County the active thunderstorms stayed mostly on mountains, producing the well-known metro donut hole.

ALERT observations (below for 24-hours ending 7:00 am) show that rainfall was sparse except for the storm cell that moved from the north part of Rincons  across the northeast part of metro and the west-central Catalinas, moving away from mountains across the Catalina area. Here at house we had only 0.05", while airport had 0.02", Atmo 0.03", and DM a Trace. Our dry July continues across many areas of southeastern Arizona.


The morning sounding at TWC (below) was taken behind the MCS and is a classic "onion" shaped sounding. As a new BL builds today it will likely remain strongly capped with little chance of storms at low elevations.

The next five days appear quite grim as the large, 500 mb anticyclone strengthens and parks itself over the West.

Friday, July 20, 2018

Storms Likely To Try To Come Off Mountains Today


View above from campus yesterday shows some buildups over Catalinas at 5:00 pm MST, as well as heavy high cloud overhead. Plot of CGs below (from Atmo and Vaisala for 24-hours ending at 1:00 am this morning) shows storms over Cochise County extending to the San Pedro Valley but not getting into much of eastern Pima County. This was just as most all of WRF variants forecast beginning Wednesday evening. Two ALERT sites in Catalinas reported rainfall right around a tenth of an inch. So essentially zero coverage for metro zone and about 10 percent or so for mountain zone. Second day in a row with high CAPE that was not realized at lower elevations. 



The nasty, shallow, well-mixed BL forecast for 3:00 pm yesterday by 06 UTC WRF runs (above) was extremely similar to the observed 5:00 pm sounding data (below). Quite amazing forecasts by the WRF versions yesterday.



Visible satellite image at 6:30 am this morning shows cloudiness and showers over southwestern New Mexico, as well as some storms in northern Mexico. The 12 UTC plot of TWC upper-air data below (from SPC) shows the strange two layer structure again below 700 mb - so question today is: can heating over lower elevations lead to a single, well-mixed BL extending up to 700 mb? The WRF runs indicate that this happens, so that storms are more likely today in eastern Pima County. The vertical wind profile, however, is not very good for the metro area, as the stronger southeasterly winds at high levels will tend to spread anvils out directly ahead of any thunderstorms.



The 06 UTC forecast runs at Atmo for composite radar coverage valid at 2:00 pm this afternoon are quite a bit different - WRF-NAM above and WRF-GFS below. The NAM forecast indicates thick anvils over the metro area and storms skirt around the low elevations. The WRF-GFS also forecasts anvil over much of metro, but with a very large and strong storm over the southern half of the ALERT network.

Appears to be at very best a flip of the coin for measurable rain here at house - will again wait and watch.

Thursday, July 19, 2018

Yesterday Mostly Down Day


Yesterday was not nearly as active as I thought it would be. Tried to believe the NAM versions of WRF forecasts yesterday, since they fit better with what I thought would happen (strong thunderstorms impacting parts of the metro area). However, Mike L pointed out in his discussion of the morning forecasts that the NAM versions were too wet and thus probably too active during afternoon. So my trying to second-guess the various model forecasts went down the tubes. More below on what went wrong yesterday. View above is of storms well north of the Catalinas yesterday afternoon.


The only sites in the Pima County ALERT network that had rainfall were in the far southwestern corner, with one gauge near Tubac recording over an inch. The plot of detected CG flashes below (from Atmo and Vaisala - for 24-hours ending at 1:00 am MST this morning) shows that most areas of southeast Arizona and southwest New Mexico were very suppressed yesterday afternoon.



Shown here are yesterday's 12 UTC and 00 UTC soundings from TWC. The morning sounding had very large CAPE and was moist to 500 mb. I expected mountain storms to develop with this profile.

However, the evening sounding (below) shows a much different situation. During the day warming and drying occurred, due to subsidence, from 300 mb down to 500 mb. There was also some drying from 500 to 700 mb, but its harder to infer the reasons for this. However, the BL situation was not good for storm development - the temperature was nearly well-mixed to 700 mb but moisture was well-mixed only to about 800 mb. The mixing ratio decreased steadily from 800 mb to just above 700 mb. It seems to me that this was due to dry air mixing downward in a layer of wind shear and possible net subsidence. No storms on the Catalinas or Rincons, but storms did develop off the Santa Ritas - close but no cigar.



Today's situation is quite challenging once again. The morning sounding (above) has a bit less PW but CAPE is very high. The WRF forecasts from 00 and 06 UTC last evening and night were all very consistent - they forecast storms to our east and also south. Very strong storms make it westward  to the Rincons but then crash rapidly. Storms are not forecast for low elevations. Interestingly, the Rincon storms do not send an outflow across the metro area (in the model forecasts) but, rather, a strong outflow pushes back eastward as the storms fall apart.

The forecast skew-T below for TWC (from the 06 UTC WRF-GFS) essentially forecasts a repeat of yesterday's shallow BL with well-mixed moisture, overlain by a deep well-mixed layer in temperature but which again has mixing ratio decreasing with height. Another deadly-suppressive thermodynamic structure, if the model forecast verifies well.

No second guessing this morning and will just observe whatever happens this afternoon.


Wednesday, July 18, 2018

Increased Chances For Storms In Metro Today


Above shows large thunderstorm northwest of Kitt Peak a bit before 8:00 pm MST yesterday evening. There was thunder at the airport, but from the north side of City we mainly watched some lightning at dark. Model forecasts were quite good from 06 UTC early yesterday, keeping storms mainly south and west of the metro area. The 24-hour CG flash density ending at 6:00 am (below from weather.graphics and Vaisala) indicates storms about where the model forecast. There were also strong thunderstorms and a number of severe wind reports in northwest Arizona and southern Nevada.

Second graphic below shows that a few ALERT gauges had rain (24-hours ending at 7:00 am this morning) through the southern part of the network, with heaviest amounts southwest of downtown.




The situation this morning appears more interesting than was yesterdays - note that drying occurred during the day (although not to degree that had been forecast) and combined with large-scale subsidence to suppress activity except along the Borderlands. The 12 UTC skew-T plot for TWC (above) indicates PW has increased again and is over an inch and three-quarters. CAPE is very large. An afternoon lifted parcel could follow the 25 C moist adiabat - a situation that usually brings severe thunderstorms here. The vertical wind profile is also very favorable, as upper winds would move anvils off to northwest of thunderstorm cores. But, if storms were to develop initially over the Santa Rita, then there could be anvil-shading problems in the metro area.

Today the upper-level IT has moved westward (12 UTC 250 analysis below from SPC), and there are two distinct anticyclone centers with one to our west-northwest and the other to our east-northeast. Between the centers there appears to be a large area of difluence over southwestern New Mexico and extending into southeastern Arizona. This situation is considerably different than yesterday's when strong confluence was occurring over the same region. The 06 UTC WRF runs are a bit different in their forecasts: the GFS version keeps storms again mainly south to west of the City; however the NAM version forecasts several severe thunderstorms to cross portions of eastern Pima County. The forecast skew-T at bottom is from NAM version and is valid at 2:00 pm this afternoon, and remains very favorable for severe thunderstorms - so hopefully it will be a much more interesting and active weather day today.



Tuesday, July 17, 2018

Yesterday's Storms - Mixed Signals Today


Thunderstorms moved across parts of the metro area yesterday afternoon - view above is from 5:00 pm MST and composite radar below is from 5:05 pm. The storms tended to split around the core metro area - here we had a rumble of thunder, a spit of rain and a bit of outflow cooling - end result a Trace. The airport however had 0.10".



Plot above from the ALERT network is 6-hour rainfall ending at 5:15 pm. As storms moved westward, most stations in west thrid of network picked up rainfall with amounts generally less than half an inch. The CG flash density plot (below for 24-hours ending at 6:45 am this morning - from weather.graphis and Vaisala) shows that yesterday was an active thunderstorm day for northern and southeastern Arizona.



Today we have the inverted trough from the east moving across northern Mexico and southern Arizona. The 12 UTC 250 mb analysis above (from SPC) shows the large scale of this IT and the strong upper winds associated with it. The water vapor image below is from 7:30 am and shows that mid to upper tropospheric dry air is wrapping around the IT from the east. The degree of drying that will occur today presents a forecast quandary.


The TWC morning skew-T plot (below - also from SPC) indicates PW at 46 mm, a much strengthened wind profile, and substantial CAPE. All in all, an excellent situation for severe thunderstorms here. However, the WRF model forecasts from Atmo indicate considerable drying by afternoon with the PW dropping a huge amount, reaching 28 mm at 3:00 pm. This drying and warming above 500 mb leaves only a sliver of CAPE by that time and storms develop to the west and south of Tucson. The 00 UTC runs are not quite so dry, but still tend to keep storms to our west and south. If the models are too dry and stable, there will be an excellent chance for storms to move from mountains across metro again this afternoon - but if forecasts are accurate we'll mostly be looking to the west at Cbs. 


Monday, July 16, 2018

Second Half July - Starts With High PW


View of Catalinas above is from 8:00 am MST yesterday showing one of the several bands of light showers that moved north-to-south across eastern Pima County during Sunday morning. Photo below is from Saturday (July 14), early afternoon showing heavy shower just north of Mt. Wrightson over the Santa Ritas.



The morning showers yesterday produced 100% areal coverage of rainfall, but with generally very light amounts. Here at house we added 0.20" to the total July amount, so far, of 0.55". The plot of detected CG flashes (below from Atmo and Vaisala for 24-hours ending 2;30 am this morning) indicates very little thunderstorm activity across almost all of southern half of Arizona. The were several flashes over the Sky Islands early yesterday.



This morning the PW remains well above an inch and a half (was 80F with high RH here at 6:30 am); however, winds aloft are light and there is limited CAPE this morning. The 500 mb analysis for 12 UTC (above from SPC) shows the huge ridge across southern 2/3rds of CONUS, with generally light winds. There is an inverted trough (IT) separating the two main centers of the anticyclone, with weak steering winds from the east over Arizona. There are also indications that cooler mid-level temperatures temperatures may sneak in today, increasing afternoon CAPE, especially for areas that get some sunshine. The 250 analysis (below, also from SPC) indicates a very pronounce, upper-tropospheric IT from western edges of Texas south-southeastward across Mexico. This feature will shift westward next couple of days, bringing increased storm activity, particularly over northern Mexico, and perhaps southern Arizona. Meanwhile, our sauna-like conditions continue.


Sunday, July 15, 2018

Sunrise Storms - 15 July


We have been away briefly and we returned last evening to find only 0.02" in the gauge, although parts of metro had clearly had more rainfall.

This morning a line of showers and thunderstorms is moving across the metro - as per NWS composite radar for 5:00 am MST above.


Rainfall data from the ALERT network (above for 6-hours ending at 5:30 am and below for 24-hours ending same time) show the sunrise showers have affected north part of metro during last 6-hours and also that total rainfall across the ALERT network yesterday was highly variable, with heaviest amounts on Catalinas, while many other spots were basically skunked yet again. 

Friday, July 13, 2018

Friday The Thirteenth - End Of Second Week In July


The most active part of state yesterday, as per detected CG flashes for 24-hours ending at 1:00 am MST early this morning (above - from Atmo and Vaisala). There were some storm cells in the metro area, although heavier rain amounts were on the Catalinas and from downtown southeastward along I-10 toward Benson. The ALERT reports below are for 24-hours ending at 5:00 am this morning (remember there are both early am showers here plus afternoon thunderstorm amounts). Here at house one small cell dropped an additional 0.05" a bit after 5:00 pm bringing amount for the day to .06". Atmo had 0.32", TUS had 0.01" and DM recorded a Trace. 

Morning sounding's skew-T plot is at bottom. The PW is down to around an inch and a half due to some drying in middle levels. There is only a sliver of CAPE today due to some warming at 500 mb and some cooling at low levels. Both variants of the WRF model ran at Atmo last night forecast storms today to stay mostly on higher elevations, and over in Cochise County. But, given the lack of steering winds and patchy cloud cover, today is essentially another crap-shoot.



Thursday, July 12, 2018

July 11 - Mostly A Donut Hole Day


Yesterday's miserable wind profile produced expected results - mountain hugging storms that quickly covered eastern Pima County with anvil cloud. The above shows NWS radar composite chart for 2:00 pm MST yesterday - which is almost as good as it got around the metro area.

However, some showers and thunderstorms developed right over the metro during the early morning hours. The ALERT plot below shows 3-hour rainfall for period ending at 5:00 am this morning. We had light showers here around 5:30 am - 0.01" in gauge vs yesterday's zero.

The plot of detected CG flashes (second below, from Atmo and Vaisala) is for 24-hour period ending 12 UTC this morning. The purple to white colors are the most recent flashes from the early morning storms.




As for today - who could believe that the large-scale features could weaken even more? The morning skew-T plot for TWC (above from SPC) remains very moist and with significant CAPE, BUT with almost no winds through much of the troposphere - and those are light westerly. The 500 mb and 250 mb analyses (below and bottom) for 12 UTC show that the Southwest has almost no height gradients and totally chopped-up wind fields. What a mess. There will be storms around again, but if one is to occur here at house it will have to develop almost overhead, but if one were to hit here chances would be good for heavy rain.