Sandy Disaster

The extra-tropical version of Sandy is over western Pennsylvania this morning, as per 12 UTC water vapor image above. The circulation of the storm is affecting almost half the country. It will be a long while before things return to normal for much of the Northeast.

Here in the quiet part of the country, lows remain in the low 40s (44F this morning) here near the Rillito - with close to 50F diurnal swings the last few days.

October is closing out with only 0.02" of rain here at the house, and that is also the total since September 11th. A very long, very dry spell continues.

More On Recent Cold Mornings

After the morning low of 36F here, near the Rillito Wash, on Friday morning, the lows have moderated a bit.  Here at the house we had 41F (56F) yesterday and 42F (56F) this morning, Sunday October 28th - temperatures in parens are lows observed at TUS. At 6 am yesterday morning it was 41F here and a mild 62F at TUS - as was nicely predicted by Atmo's WRF-GFS model (see earlier post). Substantial gradient of 21F between here and the airport. We are members of a CSA (Community Supported Agriculture) and today's news letter from Sleeping Frog Farms (below) brought bad news about a damaging freeze there on Thursday night/Friday morning.

Hello friends,
 
This week we experienced our first freeze of the season. On Thursday night, the thermometer descended to a very wintery 29 degrees and as a result, the cucumbers, beans, sweet potato greens, and summer squash were all lost. So get your fill of summer fruits this weekend, as it might be your last chance.

The farm is located in the San Pedro Valley at Cascabel, north of Benson. This is on the east side of the Rincons.

Finally, just to stay in touch with the east coast mega-storm, Hurricane Sandy is shown in the visible image below at 1345 UTC this morning. The storm is looking more like a hurricane this morning. All the media weathercasters seem to be doing their reports today out in the wind and the rain from the Carolinas to Long Island. Where will Al Roker be the next two mornings?

Two Cold Mornings

The last two mornings it has been cold here at the house and considerably colder right down in the Rillito Wash. Yesterday morning the low here was 38F, with the airport 10F warmer at 48F. This morning the low here was 36F, with airport at 47F. These were the first two mornings with temperatures in the 30s here at the house. We were in a situation this morning where the high elevation sites nearby were not nearly so cold. Morning lows at RAWS stations were: Mt. Graham at 49F; Rincon at 42F; Mt. Lemmon at 50F; and Mt. Hopkins at 55F. The early run of the Atmo WRF-GFS warms the low temperatures considerably tomorrow because of the intrusion of easterly surface winds - forecasted low for TUS tomorrow morning (Saturday October 27th) is only 60F. Will be one of those early mornings where there may be very large differences in temperature depending on what's the wind done after midnight. below is the model forecasted surface plot for 6 am MST tomorrow morning.

Below is a surface map from September 1938, showing the Great Hurricane of 1938 off the east coast. This is the storm to which Hurricane Sandy is being compared.

Where Will Sandy Head?

The big weather topic this week has been the large difference between the ECMWF and GFS forecast models. The main player is Hurricane Sandy - see IR image above from 4:45 am MST this morning. Sandy has hit eastern Cuba during the night as a Cat. 2 hurricane and is just moving back over water.

The GFS model forecasts Sandy to head into the open Atlantic while the ECMWF forecasts Sandy to evolve into a major storm event for the northeastern U.S. The two models' forecasts of surface pressures valid at 5 pm MST on Monday afternoon are shown - above is NWS GFS and below is ECMWF. The spread remains very large in some of the various ensemble forecasts. So, even at only 120-hours it is not clear which scenario will be closest to reality. A storm such as the ECMWF forecasts would, of course, have serious impacts for the most populated parts of the country. The key to how the situation evolves lies in how Sandy interacts with a 500 mb short wave that is just coming ashore over Oregon this morning. So, considerable uncertainty for millions as the weekend approaches.

Who Needs Geography 101?

Off topic but can't resist.

What's In The Future For TD 18?

TD 18 has developed in the Caribbean overnight. Visible image above shows the TD currently well south of Jamaica at 1415 UTC, 22 October 2012. In the short-term the system is forecast to strengthen and move to the north-northeast.

                                      

The current morning run of the NAM model forecasts the system to be over eastern Cuba by 84-hours (next Friday at 1200 UTC) - 500 mb above and surface forecast below. The strong short-wave in the west is forecast eventually (by ECMWF) to interact with the tropical system. The ECMWF forecasts a strong storm for the Northeast, but the GFS takes the system out into the central Atlantic. Weather chat boards starting to buzz about the ECMWF forecast.

For Arizona, looks like a taste of winter by the end of the week and a strong cold front moving across all of the state.

Rain In Southern California

Jim Means sent the following link a week or two ago  

  http://www.wrh.noaa.gov/sgx/briefing/SummaryMonsoon2012.pdf

Posted there is a very extensive, and quite well-done, summary of the summer thunderstorm season in southern California this year. It was put together by Alex Tardy of the NWS, San Diego Forecast Office.

Jim Means reports that: "The surface low pressure associated with the remains of Paul passed close enough to San Diego to generate strong southerly winds (especially along the coast) and end a heat wave on late Wednesday night/early Thursday. For example, at the North Island Naval Air Station in Coronado, the 11:52PM ob had temperature/dewpoint of 81/44, with east winds at 7; the 12:17AM ob had 72/63, with a south wind at 18 gusting to 30."
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The 15 UTC water vapor image above shows that the upper-tropospheric low west of Baja is still holding out there. Forecasts indicate that it will open into the westerlies, weaken, and be kicked out this weekend. Note the big area of dry air ahead of. Will likely bring some clouds and perhaps light mountain showers as it crosses southern Arizona.

Paul All But Gone

Yesterday's model forecasts kept Paul far vigorous than actually happened. The remnants of Paul are along the Baja coast and most of the associated clouds are being pulled into the closed low that is off to the west. Above is 10 am MST visible image for eastern Pacific, and below is 10:15 am image for the Southwest, which is pristinely clear. The WRF-GFS forecast for heavy cirrus cloud from Paul covering the south half of Arizona today certainly didn't verify. There's really no extensive cirrus cloud with Paul, since deep convection crashed yesterday evening. So it goes.

Interesting Morning At Yuma

Hurricane Paul fell apart last evening as quickly as it intensified to a brief Cat.3 status. The expected push of low-level, high dewpoint air into southwest Arizona occurred early this morning. The GoC surge came in on strong winds and reduced visibility. The Yuma observations carried visibility as low as 3/4 of a mile due to "blowing mist." The Yuma time-series of T and Td above illustrates the big jump in dewpoint temperature. The KYUX Doppler radar VAD (below) indicates that the surge is quite shallow, so that there is little threat of storms developing this afternoon. The early WRF-GFS does forecast isolated showers tomorrow afternoon (Thursday, October 18th) along the Borderlands from Nogales westward.

The shallow marine layer that blew ashore is apparently trapping the KYUX, first-tilt, radar beam and there's a large area of "echo" detected by the radar - see below. Some of this is ground clutter, but some of it may be due to dust and sand and etc., due to the gusty winds. The very strong echo to the northwest is apparently the San Bernardino Mountains, northwest of Palm Springs, California. This an unusual and interesting situation, not seen very often.

Paul About To Make Landfall

Hurricane Paul has moved rapidly northward during the night and headed a bit to the east of the expected track. The hurricane is about to make landfall on the coast of southern Baja as a Cat.2 storm. The above visible satellite image is from 7:30 am MST this morning. Paul is expected to turn markedly to the west after 24 to 36 hours and dissipate within the mid-level closed low that has been nearly stationary west of Baja. The gradients in clouds and moisture remain very strong along the US/Mexico border. Dewpoints are in the middle 60s at the north end of the GoC, but only in the upper 40s at Yuma. The image below is a WRF-GFS forecast, on the 5.4 km grid domain, from the early run this morning. The forecast is of OLR (outgoing long-wave radiation) valid at noon tomorrow (the 17th of October). The forecast, if it verifies, indicates high-level clouds from Paul over about the southern half of Arizona tomorrow.

The same run of WRF-GFS forecast for 700 mb RH valid at midnight tomorrow night is shown above - indicating that higher RH values associated with Paul will just move into the Borderlands of southeastern Arizona. The forecast for total rainfall through midnight on Thursday night is shown below, with very large amounts forecast for Sinaloa and parts of Sonora and Baja. The model keeps the rainfall south of the border. So the large scale pattern is forecast to block the northern progression of Paul and keep the storm's rain out of Arizona. After the weekend, the 500 mb low that absorbs Paul may be kicked out of place and affect Arizona.

Paul Intensifies Rapidly

Hurricane Paul has intensified rapidly today and is now a Cat. 3, major, hurricane - above is 2030 UTC visible satellite image. Latest NHC track forecast has shifted a bit to the east and is shown below.

Paul Becomes Hurricane

Hurricane Paul (Cat. 1) is now moving north. A substantial trough extends northeast of Paul and cloudiness extends north to southeastern Arizona and northeastward over Texas. A substantial area of strong convection was occurring at 12 UTC at the south end of Baja (see IR image above). Paul is forecast by NHC to move northward (see graphic below) to near the Baja spur before weakening dramatically. Paul's track and the extensive activity to its northeast will trigger a push of low-level moisture northward up the GoC today and tomorrow. This push of higher dewpoints will make it into southwest Arizona by Wednesday morning and it may even begin showing up tomorrow. The impact of this surge is uncertain, since it will likely be shallow. It is something to watch the next couple of days.

The NAM forecast (below, for 700 mb valid at 12 UTC Wednesday morning) indicates a persistent ridge over Arizona. The flow around this ridge keeps deeper moisture with Paul to the south of the border. Once again, the synoptic pattern is fighting the tropical system, trying to keep significant moisture south.

Chilly Mornings This Weekend

Above photo is of a cottonwood just turning gold at Santa Rita Abbey, about 5 miles northwest of Sonoita. There was fairly heavy frost on the car out there yesterday morning (Saturday, October 13th). The lows here at the house were 42F both Saturday and again this morning. I noticed a number of temperatures in the 30s this weekend across the RAWS stations in southeast Arizona. We're now going into the time of year when I try to make it as long as possible before I switch over to the heating system.

Tropical Storm Paul, see above and below, is located well south of 20 degrees north this morning. The associated cloud shield is fairly large. The NHC anticipates that Paul will become a hurricane and will start moving northward in a day or two. So, Paul could be in our future. However, the NHC forecasts for tropical storms that began in very weak steering flow have not verified well this season - so I'll hold off showing the NHC forecast tracks for now.

Mostly Skunked Again

Yesterday's event (11 October 2012) mostly avoided southern Arizona. What showers and rain there was tended to occur, at lower elevations, during the morning yesterday. At 10 am MST there was a bright flash and a tremendous crash of thunder here at the house - I heard it without my hearing aids in! There were several very light showers and 0.02" ended up in the gauge. And that was the "event." The above photo shows what appears to be a heavy rain shaft over the Catalinas at 10:30 am MST. Atmo also recorded 0.02", while DM and TUS had traces. Only four of the ALERT stations in eastern Pima County had rainfall and those were in the Catalina Mountains, with a max of 0.08" (note that the ALERT minimum amount measured is right at 0.04", so there were probably other slight amounts around the lower elevations). Most of the southeastern Arizona RAWS stations to the east and northeast of Tucson had light rainfall. Only two amounts were over 0.05" - with the RAWS station on Mt. Graham coming in with the heaviest amount I found - 0.15". Some low clouds are hanging on the mountains this morning, as the Kitt Peak web cam shows below at a bit after 7 am MST. I looked at the WRF-GFS low temperature forecasts for tomorrow morning and it appears that it will likely be the first morning of the Fall with lows in the 40s here at the house.

The final, trailing part of the short wave at 500 mb does not cross by until tomorrow morning, but model forecasted showers stay to the north, except for a tiny amount predicted by the WRF-GFS on the top of Mt. Lemmon. So it goes for our first chance for some October rain here.

Light Showers At Sunrise

Off to a slow start today. There were light showers at sunrise this morning here at the house, but only a trace. The visible satellite image (above from 8:30 am MST) shows that the Pacific system is still off the California coast. Considerable cloudiness and shower activity has developed over Nevada and Arizona ahead of the system. The model forecasts (NWS NAM) indicate that the system may move across Arizona a bit slower than earlier forecasts had indicated. Below is 500 mb forecast valid at noon today (11 October 2012).

The NAM 500 mb forecast for midnight tonight is shown above, indicating the system still well to the west. Below is the CIRA blended PW analysis valid at 8 am MST this morning. It indicates a nice plume of PW values of 1.0 to 1.5 inches extending from the GoC into southwestern Arizona. The morning run of the NAM is more aggressive wrt precipitation over southeastern Arizona with this system than is the early WRF-GFS, which keeps precipitation mostly to the north. Now, we'll just watch to see how this event plays out.

500 mb Closed Low Moving Down California Coast

The closed low off the California coast is moving slowly southeastward this morning, much as various models have been forecasting the last several days. The issue continues to be how much lower-tropospheric moisture can this system pick up before it ejects northeastward? Slower movement is good, and it would help if it moved further south than models currently predict. The above graphic is the 12 UTC 500 mb analysis this morning from NCAR RAL.

The system is now within the forecast range of Atmo's early WRF-GFS. The run from 11 pm last evening forecasts the precipitation with this system will skirt by most of southern Arizona. The model forecast of PW at 5 pm MST tomorrow afternoon (Thursday, 11 October) is shown below. The model forecasts values to increase to around an inch from the Tucson area eastward, certainly not a very wet system in the current forecast. The NWS NAM model run at the same time last night kept rainfall east of Tucson.

The WRF-GFS forecasts one light streak of rainfall across eastern Pima County, but keeps more significant rainfall off to the east and northeast (below is total rainfall forecast from WRF-GFS through 7 am MST on Friday morning. I see that the new NWS NAM forecast is quite similar. So, a system to watch carefully, but clearly it will produce more weather across northern Arizona than it does down here in the south.

Showers Later This Week?

Was a very nice sunset yesterday (8 October 2012), with the Catalinas glowing in shades of purple to orange. Another cool morning here at house with low of 52F; down right along the Rillito Wash  it was at least 5F cooler, so temperatures down there were in the upper 40s.

The closed low at 500 mb that's been parked off the West coast is now moving slowly south, as a new storm approaches from the north-central Pacific. The 1600 UTC water vapor image above indicates that the upper-tropospheric cyclone is located west of San Francisco. This morning's forecast for 500 mb from the NAM indicates the center of the circulation coming over southern California, north of San Diego, by Thursday evening. The 500 low then heads northeastward in the model forecasts, with a cold front and band of showers moving across Arizona Thursday night. The NAM forecasts some light rainfall amounts over southeast Arizona by Friday morning. The key to this event will be moisture availability and instability. The eastern Pacific blended PW product for 12 UTC this morning (below) indicates that values are increasing in a plume to the south and southwest of the 500 mb low. So, we need to keep track of how the low-level moisture inflow develops as the system moves into southern California tomorrow and Thursday.

Blocked Up Pattern

Last April and May we had a large-scale pattern that jumped back and forth between Omega and Rex Blocks from the eastern Pacific to central North America. The atmosphere has returned to that pattern this Fall for the last few days. The above is last evening's 500 mb chart (00z anal 7 October 2012, from the GFS). The pattern exhibits a very distinct Rex block over the eastern Pacific. The block gradually weakens during the next few days, as the cyclone at 40N is kicked eastward. That cyclone at 500 mb will impact the Southwest during the coming week as it moves inland; however, models are keeping it as a fairly dry system.

Repeat from last Spring:  Historical note - The Rex Block was named for Commander Daniel F. Rex, Office of Naval Research. Rex studied large-scale blocking patterns under Carl-Gustaf Rossby at the University of Stockholm and received his Ph.D. in 1951.

Touch Of Winter On High Plains

Some winter weather occurring this morning over the High Plains of northeast Colorado, western Nebraska and southeast Wyoming. Above web cam view is just after 8 am MST; surface plot below is from just before 8 am MST. A classic, weak-upslope event with quite high surface pressures. Looks like the roads are mostly wet with this early snow.

September Summary

It is a nice, cool Chamber of Commerce morning in Tucson today (Friday, October 5th). The low temperature here at the house was a pleasant 51F (coolest morning so far this Fall). High temperatures are still going into middle to upper 90s though. The month of September saw the summer storm season end around the middle of the month. The last rainfall here at the house was 0.23" on the 11th of September. Total rain here for September was 0.70" (with other significant amount being 0.35" on the 1st), so the amounts for the summer posted previously in mid-September are the way that things ended for June - September. The NWS summary for September rainfall is shown below, from their web page.

Finally, TS/Hurricane Nadine is history. First NHC statement was on September 11th and the final statement was issued at 11 am AST on October 4th. Not the longest storm on record, but certainly a long-lived one.

Denver Weather

Looks like a strong Canadian cold front is going to converge with the POTUS candidates, and a lot of political hot air, in Denver later this afternoon. Above is 1830 UTC surface plot from NCAR RAL - cold front currently moving into southeast Wyoming before taking a serious plunge down the Front Range. The forecast - 100% chance of low-level turbulence!

Days Over 100F

Edited to add: High temperature at TUS yesterday reached 99F, so number of 100F and higher days stayed at 73 for 2012.

Interesting graphic from the NWS web page above, showing days per year with highs of 100F or more. Going into today the count for 2012 is 73. One more occurrence will put 2012 into the top 10. Below is 2115 UTC visible satellite image showing much of the West and Southwest to be experiencing CAVU conditions!