Saturday, August 13, 2022

Little Change



Heavy anvil cloud cover yesterday afternoon at 4:10 pm MST acted to limit storm activity over our region.  Plot of detected CG flashes (below - from Atmo and Vaisala) shows minimal thunderstorm activity over far eastern Pima County, Santa Cruz County, and western portions of Cochise County.



Rainfall reports from the ALERT network (above and below for 24-hours ending at 7:00 am this morning) indicate scattered coverage, with much of main metro area rain-free. There were only 8 sites with half an inch or greater rainfall, and I estimate areal coverage at around 30 percent. Here at house there was a brief shower before midnight last night which produced only 0.01".



The 500 mb pattern remains chaotic, with center of anticyclone circulation about over Goodland, Kansas (the sounding for Denver has been missing for an extended period due to helium shortage at the station). There appears to be a very weak, west to east trough across Arizona. The morning sounding (below) indicates the presence of weak, westerly steering winds. Afternoon activity will likely be driven by outflows, but with anvils again spreading to the north of storms.


Forecast below is from the WRF-RR run at 12 UTC this morning and shows model forecast of rainfall through midnight tonight. There's a bit of a donut hole over us, and generally reduced storm activity, relative to yesterday, over much of Arizona. Two graphics at bottom show the NWS Forecast Office outlook for today is more aggressive than is the WRF model. 




Friday, August 12, 2022

Weekend Storms?



Clouds over the Catalinas again this morning at sunrise.

Plot of detected CG flashes (above, from Atmo and Vaisala) for 24-hours ending at 0733 UTC (12:33 am) this morning shows minimal storm activity over Pima County. The one cluster near Rincons was apparently over Redington Pass area. The ALERT map of rainfall (below, for 24-hours ending at 7:00 am MST) shows isolated spots with 0.04" or more - most significant cluster being over Redington Pass.

There were two other reports in southern part of network - 0.39" at Tinaja Ranch west of Green Valley, and 0.04" at Elephant Head east of Amado (view of Elephant Head looking south is at bottom).



Morning sounding from TWC/TUS (above) remains moist and unstable, with only a small amount of lifting needed to trigger storms at lower elevations. Winds aloft profile indicates very weak steering winds, so strong but slow moving storms could produce heavy rains.

Forecast below (from 12 UTC WRF-RR) is for rainfall through midnight. Model puts most of Tucson in a donut hole. Second below is rainfall through 5:00 pm on Sunday from the 06 UTC WRF-GFS - showing the donut hole persisting.




Thursday, August 11, 2022

Overview Past 24 Hours



Limited time this morning, but here's a quick overview. Cloud cover this early morning at 5:42 am MST.

Considerable thunderstorm activity over the metro area yesterday, as the models prevail again (above plot of detected CG flashes from Atmo and Vaisala).

ALERT rainfall for 24-hours ending at 7:00 am this morning - a widespread event, with numerous reports over half an inch. Here at house we received only 0.02"; airport had 0.08", Atmo reported 0.31", and DM had 0.37".


Little change at 250 mb (above) this morning - anticyclone center has shifted slightly eastward. The morning sounding for TWC/TUS (below) continues moist and unstable. It appears that amount of heating will be important today for storm development, as morning cloudiness is persisting after yesterday's rains.


But, the forecast models manage to develop storms again today. Forecasts from the 06 UTC WRF-GFS: above composite radar echoes at 8:00 pm this evening, and below rainfall through midnight.


Wednesday, August 10, 2022

Another Stormy Day



Sunrise color over the Catalinas at about 5:50 am MST this morning.

Storms and rainfall were scattered around the metro area during past 24-hours, as per the ALERT maps (above and below) for the 24-hours ending at 7:00 am this morning. Rain fell at spots both in afternoon yesterday and around midnight also. Here at house we were avoided by all storms with no rain in the gauge this morning.

There were some storms in Arizona with severe wind gusts yesterday - these were mostly around the Phoenix region, One site reported a measured gust to 76 mph at Peeples Valley, north of Wickenburg.


The 500 mb pattern remains very chopped up with minimal height gradients and light winds. The 250 mb morning analysis (above) shows the upper-tropospheric anticyclone amplified and shifted north, to be centered about over the Uinta Mountains of Utah.

The TWC/TUS morning sounding (below) remains moist, but with limited CAPE and wind speeds mostly 20 kts or less. When I estimate afternoon conditions using this sounding, I come up with almost no CAPE available this afternoon. However, my forecasts so far this month have not been good, and the models are again more optimistic than I am.


Forecasts here from the 12 UTC WRF-RR runs at Atmo. Forecast of composite radar echoes (above) is valid at 7:00 pm this evening. Precipitation forecast (below) is for rainfall through midnight tonight. Regardless, yet another interesting weather day for us.


Tuesday, August 09, 2022

Midnight Storms



Pre-sunrise view of the Catalinas after another night with storms around midnight - third consecutive night. Plot of detected CG flashes (below - from Atmo and Vaisala) shows significant thunderstorm activity over much of eastern Pima County.

The 24-hour plot of rainfall at ALERT sites (second below) shows the the northeast half of the network received measurable rainfall - four additional sites in the corner had rainfall over 0.04" but less than 050". Here at house we had heavy rain with the total gauge amount at 6:00 am being 0.78", the heaviest single event total for the entire year. I count 18 sites with over an inch of rainfall.



Little change at 500 mb as the pattern remains quite stagnant (above).

The morning TWC/TUS sounding (above) remains very moist and unstable. The choppy wind profile will probably support storm movement from the southeast. The forecast for composite radar echoes (below - from 09 UTC run of the WRF-RR) is valid at 4:30 pm MST this afternoon - possibly a fourth day with storms here.

The morning forecast from the NWS Tucson office (second below) has POPs of 40 to 60 percent for every forecast period during the coming week. Quite a start to August with over an inch and a half of rain here at the house.



Monday, August 08, 2022

Early Morning Storms



Thunderstorms moved across the metro area after midnight this early morning. Image above shows CG flash over northeast Catalinas. Radar below (from NCAR RAL) is for 0658 UTC - about the time of the flash shown. The plot of detected CG flashes (second below - for 24-hours ending at 1203 UTC) shows a focus of thunderstorm activity over eastern Pima County (from Atmo and Vaisala). 



Rainfall was widespread across the ALERT array with a considerable number of reports of 0.50" and more. Here at house there was 0.32", which fell after midnight. I was doubtful that the BL could recover after the rain of the 7th - but models were better (although about 6 hours too early), and I was wrong.

There were also a number of severe thunderstorms in Arizona yesterday. There were 6 reports of large hail (greater than inch in diameter) around Sierra Vista. There were also 7 reports of severe winds around Buckeye, west of Phoenix, where mesonet stations recorded gusts over 75 mph.


The 500 mb chart is quite interesting this morning (above) because of the nearly complete lack of height gradients. Looks like height range from California to Southeast is only from 588 to 593 dm. The western anticyclone circulation center is about over Lake Powell. The morning TWC/TUS sounding (below, from SPC) is distinctly onion shaped. Afternoon heating will probably lead to a BL with almost no CAPE.


So, I am again in the position of doubting the model forecasts. The 09 UTC WRF-RR forecasts for composite radar echoes above is valid at 7:00 pm MST this evening, while forecast below shows the model's total rainfall through midnight tonight. Will the models prevail again today?

Sunday, August 07, 2022

Severe Thunderstorms



Colorful skies this morning just before sunrise - above from about 5:30 am MST.

There was significant thunderstorm activity across the metro area last night - plot of detected CG flashes above is for 24-hours ending at 1003 UTC this morning. There were 5 reports of severe winds last evening in Arizona. Four of these were around the airport (airport recorded a gust to 60 mph at 9:16 pm) and the other was east of Tombstone. The IR satellite image (below from NCAR RAL) at 0532 UTC shows a very large MCS over Sonora, extending into southeast Arizona.


Rainfall was widespread across the metro area as per the ALERT charts for the 24-hours ending at 6:00 am this morning. Reports were generally less than half an inch - 0.09" here, 0.10" at Atmo, 0.05" at DM, and a  Trace at the airport.


The morning sounding for TWC/TUS (above) has less PW and CAPE than did yesterday's; and the onion-shape indicates that downdrafts behind the storm activity have had a drying impact. The main question for today will be whether or not the BL below 700 mb can recover and support intense storms later today.  I have my doubts given the usual scenario after widespread rain across the low elevations.

However, the early WRF runs at Atmo are forecasting storms for eastern Pima County - above forecast from the 06 UTC WRF-GFS is valid at 5:30 pm. The model does forecast the most intense activity and strong to severe winds occurring out west of our area.

A special morning graphic and the current forecast from NWS (two graphics below) emphasize the likelihood of severe thunderstorms, as well as blowing dust (given the wet ground over much of metro the threat of blowing dust would likely be out in central and western Pima County).

I'll be very interested to see what actually transpires this afternoon and evening!