Monday, June 26, 2017

Diminishing Thunderstorms For Southeast Arizona

Yesterday thunderstorm activity occurred a bit further west than the WRF-GFS forecast indicated - but no CAPE at low elevations as per the model's forecasts. Graphic above ( and Vaisala) shows CG flash density for 24-hours ending at 06:00 am MST this morning. Storms surrounded the metro area, but the real action was far off to the east over New Mexico and Texas Panhandle, where there were many severe storms.

Dora has become a Category 1 hurricane this morning and is located south of Cabo Corrientes (IR image above from 06:00 am also). The morning track forecast from NHC is shown below. As the 500 mb anticyclone migrates westward across northwestern Mexico, it forces Dora to turn westward, and her chances of significantly affecting southern Arizona are rapidly diminishing.

This morning's skewT plot of TWC upper-air data (above) continues to keep PW over an inch - but there is little CAPE and drying will begin later today - so much diminished storm activity today off to our east. Below is 500 mb forecast from the 06 UTC WRF-GFS run at Atmo - valid at 08:00 pm tomorrow. The 500 mb anticyclone is forecast to be centered west of northern Baja, with hot dry flow into the Southwest from the Pacific. A really nasty pattern that will mostly continue our long run of 100+ F days.

Sunday, June 25, 2017

Storms Around But On The Mountains

Radar above is composite for about 02:30 pm MST, while Kitt Peak view to the south below is from about 04:30 pm. High-based Cb just visible far to the south.

Complicated Situation Today

Yesterday's WRF-GFS forecast of significant thunderstorms over southwest New Mexico proved quite good - above is El Paso composite radar at about 07:00 pm MST yesterday evening. These storms produced quite a few severe reports. The plot of detected CG flashes below (from Atmo and Vaisala) shows that thunderstorms impacted parts of Cochise County, but generally remained well away from Tucson Metro.

The forecasted increase in moisture from the east also verified, with a shift of winds to the east and Td jump at the airport a bit after 10:00 pm last night. The moisture increase, as well as abundant debris clouds, kept the temperatures hot through the night - temperature here at house at 06:00 am this morning was 90 F.

The morning TWC sounding plot (above) indicates several substantial problems that need to moderate during the day, if thunderstorms are to occur in the local area. The wind profile is very weak and chopped up below 500 mb. The near surface moist layer extends up to only 850 mb, with a very hostile residual BL above to 500 mb. Little chance for surface parcels to break through that, unless deeper moisture moves in from the east.

The 06 UTC run of the WRF-GFS keeps storm activity off to the east and south today, and its forecasted soundings at TWC remain unfavorable. Below is the model's forecast of precipitation through midnight tonight.

And far off to our south, TS Dora has formed (above) and is forecast to become at least a storm while heading toward the south end of Baja (below). Dora has the potential to be the feature that triggers the first significant GoC moisture surge of the summer. Depends of course on actual track and intensity of the system. But the WRF-GFS, on 5.4 km grid, forecast of PW (valid at 11:00 am on the 28th) - bottom - indicates some potential for a surge by Wednesday morning.

Saturday, June 24, 2017

Low-Level Moisture From The East This Weekend

Debris cloud providing sunrise color again this morning.

Surface chart below is from NCAR at about 07:30 am MST - note higher dewpoints to the east and the strong east-northeast winds, especially over west Texas. Pressure gradient from New Mexico/Texas border over to Tucson is quite strong, with pressure to our east more than 10 mb higher.

The morning TWC sounding plot above indicates two old BL residual layers aloft that reach above 500 mb, with generally westerly winds. The 500 mb temperatures are quite cold wrt the forecast high today of 113 F. Thus, there should be some mountain buildups closer to the metro area today.

The sounding forecast below is from Atmo's WRF-GFS run at 06 UTC. The sounding exhibits a single, well-mixed BL that yields convective cloud bases around 500 mb, with only about 4-5 g/kg mixing ratio in the sub-cloud  layer. The forecast sounding is quite classic for dry microbursts, if light showers develop over the mountains.

The model continues to forecast widespread thunderstorms over southwestern New Mexico this evening - composite radar echoes above are valid at 07:00 pm. The PW forecast below, valid at 10:00 pm, indicates outflows bringing considerably higher PW into southeast Arizona, so that tomorrow could be an interesting storm day.

Friday, June 23, 2017

Yesterday's Sounding/Brief Look At Today

Shown above is the skewT plot for TWC's 00 UTC sounding data yesterday (see previous post re evolution of BL yesterday). The WRF-GFS forecast sounding was much better than my subjective forecast that the elevated residual BL and SFC BL would merge into single BL. Model forecast was quite good, except for being a bit too moist in surface-based BL. High "only" reached 109 F yesterday. Neither the old elevated or the surface-based BL had any CAPE by 00 UTC.

Nice sunrise this morning - when I returned from morning walk at 06:00 am, temperature here at house was 83 F, nearly same as airport's 84 F - yuck.

This is one of those days when the most interesting weather events are occurring off to our northeast. The 07:00 am surface plot above indicates a strong cool front moving south along the Front Range - already reaching into the northeastern corner of New Mexico. Visible image below from about the same time shows the associated low clouds backed up against the Front Range. (Note also the large areas of smoke from the numerous wildfires burning in the Southwest.)

When this front "back-doors" across southern New Mexico, issues will be: how far west will it make it? and how widespread will be the thunderstorms it triggers? Models this morning suggest fairly widespread storms in southwest New Mexico tomorrow afternoon, that push moist outflow westward into southeastern Arizona, making a chance for storms in our area by Sunday.

Thursday, June 22, 2017

Moisture Up Some/Temps Down A Bit

Extreme heat (115 F yesterday) and more wildfires, with homes lost, around Sonoita dominated the news yesterday. Moisture from the GoC has gradually increased due to the persistent heat low and typical diurnal wind circulations - the WRF forecasts had indicated this several days ago. The 500 anticyclone is centered just off to the northeast and it looks to be another grim day for southeast Arizona and much of the Southwest.

Had a power surge here - probably as demand increased rapidly as people got up to 90 F temps - and have just gotten PC back to life. Will take a quick look at soundings this morning. The 12 UTC skewT for the TWC upper-air sounding is shown above. The increase in moisture shows up below 750 mb - also in T trace. Residual boundary layers (BLs) seem to reach well above 500 mb. When I estimate the afternoon BL, I see just a tiny bit of CAPE over low elevations.

Below is forecast TWC sounding from Atmo's 12 UTC WRF GFS forecast run valid at 04:00 pm MST this afternoon. The model forecasts a surface-based BL to reach only to about 700 mb with well-mixed moisture at 8 g/kg. That is overlain by a hotter, drier, elevated BL - apparently from higher elevations to our north, as per the winds in that layer - that significantly caps the surface BL. 

The questions is whether or not the two BL structure can actually persist today. I think that a well-mixed surface layer with 8 g/kg is probably quite unlikely - something closer to 6 seeming more likely. Thus, the afternoon atmosphere may be one in which the two BLs of the forecast have merged into a single, deep BL that reaches to around 500 mb. This would lead to build ups around highest mountains and more evening cloud debris over the deserts.

Wednesday, June 21, 2017

Thunderstorms Much Closer To Metro Area This Afternoon

Shown here are radar, visible satellite image, and CG flash density for 6-hours - all at or ending right around 04:00 pm MST.

More Heat Today - Not Much Yesterday Other than Heat

Another very warm morning with temperature here at house around 80 F at sunrise.

 Radar echoes did indeed surround Tucson yesterday afternoon - graphic above shows echo tops at 05:15 pm MST. Since cloud bases was nearly 15,000 ft, the showers near Tucson were not very deep. Deeper storms tended to stay east to south of the radar. There were gusty outflows here, although not as strong as the WRF forecast, and they did nothing to ease the 116 F heat. There was a report of a downburst wind gust over 70 mph near Nogales.

The CG flash density plot below (from and Vaisala) indicates that thunderstorms generally stayed over or very near the mountains.

With the strong heat low persisting over the Southwest, moisture is slowly creeping northward up the GoC - as per the MIMIC total precipitable water analysis below. The very high values in the GoM are associated with Tropical Storm Cindy, which is heading in the general direction of Lake Charles, Louisiana.

Tuesday, June 20, 2017

Very Hot But Interesting Day On Tap

Third hottest day on record here in Tucson yesterday at 115 F. Was very warm at sunrise (one of my warmest morning walks ever), with hazy, dusty, smokey skies and lingering clouds.

Middle and high level moisture increases have brought PW up to around an inch and the 6 UTC forecasts from Atmo's WRF-GFS model are indicating an interesting day, even with the very high temperatures. The forecast of composite radar echoes above is valid at 06:00 pm MST this evening. The model forecasts storms to surround a low-elevation, metro donut hole. The forecast sounding (below) is valid at 03:00 pm. The sounding has just over an inch of PW and mixed layer CAPE greater than 500 J/Kg. Cloud base would be way up at about 550 mb indicating strong potential for local downbursts.

The 10m wind forecasts from the model (above valid at 05:00 pm and below valid at 08:00 pm) indicate strong outflows across the metro area before dark, with some winds to our north and northeast possibly reaching severe levels.

However, the model forecasts little cooling with the outflows - 2m T forecasts here are valid at 03:00 pm (above) and at 8:00 pm (below). Airport does drop from 111 to 95 F and the accompanying increase in RH would make for a miserable evening. Time will tell how all this actually evolves.

Monday, June 19, 2017

Dangerous Heat Continues

Dangerous heat continues with 700 mb temperatures over the Southwest at or near 20 C, which is very hot for that level. High temperatures at the airport for last five days, beginning Wednesday, June 14th, have been: 103, 106, 105, 105, and 108 F.

There is some chance for dry thunderstorms over the mountains near the New Mexico border the next couple of afternoons - not good given the large number of wildfires already burning. Image above is from Saturday afternoon and shows the smoke plume from the Frye Fire, which is burning on the north slopes of Mt. Graham, west of Safford. Image at bottom shows the plume, shifted a bit toward the north, yesterday afternoon.

Friday, June 16, 2017

Cool Mornings, But ---

It was about as dry as it can get yesterday afternoon in Tucson area. Surface observations at the airport (above) were indicating RH of 1 %. The Td measurements by the NWS ASOS are least accurate when values drop below 0 C, and what we can say with certainty is that the RH fell to extremely low values.

Here at the house, morning low temperatures have been quite cool and very pleasant - lows last three mornings were (with airport highs in parens): 14th 52 F (103 F); 15th 54 F (106 F); and 16th 56 F (TBD). With the 50+ F diurnal temperature swings, afternoons have seemed brutal.

The current NWS forecast for the next five days (below) indicates things will get considerably worse. Take care.

Thursday, June 15, 2017

Very Dry

Atmosphere is very dry over the Southwest, with PW for the morning Tucson upper-air sounding at only about 4 mm - RH yesterday afternoon dropped to near zero values (only 2% during late afternoon). Very nasty.

I peeked at the 00 UTC forecasts from Atmo's WRF-GFS model. Shown below is the forecast of PW valid at noon on 22 June next week. Bit of hope in that forecast, as higher PW creeps northward up the GoC and sneaks into parts of Arizona.