Saturday, July 24, 2021

Damp And Dreary Morning

View toward Catalinas from campus at 7:00 am MST this morning, Below is visible satellite image from 1430 UTC (7:30 am) showing large swirl of cloudiness within southwest sector of closed low.

Plot of detected CG flashes (above for 24 hours through 7:00 am - from Atmo and Visala) indicates no thunderstorms over southern Arizona since yesterday afternoon. Widespread rain across the metro area (below, from MesoWest for 24 hours through 7:55 am), with some amounts reaching just over an inch.

I have not ventured out to gauge yet, as rain here continues - will fill in amount later this morning.

Still raining lightly at noon - amount now in gauge 0.54".

At 500 mb (above) the large cyclone is centered between Tucson and Albuquerque. Low is forecast to move slowly toward the southwest and cross over the Tucson area. The morning TWC/TUS upper-air sounding (below) is nearly saturated through the troposphere, with northeast to northerly winds. While the SPC analysis indicates CAPE, it is an over-estimate and what CAPE there is is just a sliver.

Radar (second tilt - 1.3 degrees elevation) above is from 7:47 am, and it indicates a considerable area of echo extending from Cochise and Pima Counties, reaching almost to Phoenix.

Below is 06 UTC GFS forecast for total rainfall from today through the end of the month - so we will end up having very wet totals for July.

Friday, July 23, 2021

Rillito Photos This Morning

Data plot from USGS river flow gauge at Dodge and Rillito at 6:15 MST this morning. Photos from the loop path about half an hour later. It's been a very long time since I've seen the Rillito running like this!

Heavy Rains Last Night

Bit of color at sunrise after a night with widespread heavy rains across the metro area.

Radar above from just after midnight shows heavy storms that were moving across the metro area. Plot of CG flashes (below for 24 hours ending at 7:03 am MST - from Atmo and Vaisala) shows eastern Pima County nearly covered by the flashes.

Rain amounts across the ALERT network were very high, with more than half the sites reporting more than an inch of precipitation. A site on the west end of the Catalinas reported over 4 inches, and there were many sites with more than 2.50". Here at the house we had only 1.17".

At 500 mb this morning things are a bit chopped up because of the storms. The weak cyclone is now centered in west Texas, with quite cold temperatures in its southern portions. Models forecast the low center to be nearly over Tucson by Sunday morning. The west wind at Tucson is due to a mescoscale convective vortex (MCV) left behind by the storm complex. Visible satellite image below is from 1501 UTC this morning.

The TWC/TUS morning sounding (above) shows a classic onion shape (as per Zipser, Mon. Wea. Rev. 1977). This sounding has no CAPE and a strange wind profile because of the convective modifications. I would expect that today will be suppressed, as is typical, because of the widespread rains and wet surface conditions keeping heating down. However, the morning forecast from NWS (below) continues with very high POPs for each period through Sunday.  

Thursday, July 22, 2021

Flash Flood Watch Through Saturday

Atmo webcam captures a UFO at about 7:00 am MST this morning!

Thunderstorms mostly avoided the greater metro area yesterday, as per plot of detected CG flashes (above, from Atmo and Vaisala) for 24 hours ending at 1:13 am this morning. However, many sites in the ALERT area (below) measured rain from showers - although heaviest amounts were down in the southwest corner of the network, where there were thunderstorms.

At 500 mb this morning (above from SPC) anticyclone continues to be centered somewhere near the Four Corners. There is a weak, elongated cyclone centered near Abilene, Texas. This feature is forecast to move slowly westward, and be nearly overhead Tucson by Sunday morning.

The 12 UTC TWC/TUS sounding plot below continues to have substantial, low-level CAPE. Wind speeds are light below 500 mb and anvils would be moving out to west of any storm cores - i.e., a potentially negative factor for storms over the metro area. The observed PW this morning is 34 mm, but the 06 UTC WRF-GFS forecasts PW to have risen to 44 mm by 11:00 pm tonight.

Above shows current morning forecast from NWS, with probabilities for measurable rain at the airport.

Finally (below, also from 06 UTC WRF-GFS is forecast for accumulated rainfall through 5:00 am tomorrow morning - the 3.3 inches is one of the highest amounts that I can remember for the airport. Amounts are not nearly as high on the two 12 UTC WRF runs I looked at.

All-in-all, an interesting few days on tap.

Wednesday, July 21, 2021

Wet Week Continues

Couple of lenticulars over the Catalinas at sunrise this morning.

ALERT data (above) shows rainfall for 24-hours ending at 7:00 am MST this morning. There were 7 sites with half an inch or more, but none over an inch. Here at house we had thunder and a shower a bit before 8:00 pm that left only 0.10" in the gauge; TUS had 0.01"; DM 0.03", and Atmo got a heavier shower with 0.46". Thunderstorm areas in eastern Pima County indicated below on plot of CG flashes (from Atmo and Vaisala) detected during 24 hours ending at 2:30 am this morning.

Map of TPW at 13 UTC (above) shows very high values well up the lower Colorado Basin and most of southern Arizona. The swirl at 120 W is remnant low from Tropical Storm Guillermo. 

Flash Flood Watches are in effect for parts of Arizona, New Mexico, and Colorado. Watch in Arizona is valid Thursday night through the day Saturday.

The morning 500 mb chart (above) shows anticyclone centered near Four Corners and weak short wave eastern New Mexico. By midnight Saturday night the shortwave is forecast to evolve into a slow moving, closed low over southeastern Arizona (below), that brings the threat of heavier rains into the weekend.

Tuesday, July 20, 2021

Showers After Midnight

Light showers and some thunder affected much of the area, mostly after midnight, last night.

ALERT network observations (above) for 24 hours ending at 7:30 am MST this morning. Looks like about half of the sites had 0.04" or more. Here at house we had only a Trace; Atmo measured 0.21"; TUS 0.16"; and DM 0.11".

Composite radar image above is from 2:43 am, showing the scattered nature of the echoes over our region. Plot of detected CG flashes (below, from Atmo and Vaisala) shows that some of the echoes were thunderstorms.

The morning 500 mb analysis (above) shows the anticyclone is centered over southwest Colorado, and is quite elongated from southwest to northeast. The 12 UTC sounding plot for TWC/TUS (below, from Univ. of Wyoming webpage) continues very moist and unstable - note that PW is just over two inches. Easterly winds have increased some, with steering winds around 20 to 25 kts). Visible satellite image at bottom shows skies to be mostly clear over the eastern half of Arizona.

Storm development today will be driven by orography and heating. Model forecasts indicate limited storm activity for eastern Pima County; however, the general situation appears basically similar to last few days.

Monday, July 19, 2021

Rainy Week

View of the Rillito about 6:00 am MST this morning - gauge at Dodge indicated that flow exceeded 5,000 CFS early this morning. Most flow I've seen in the wash in many months.

Plot of CG flashes detected (above - from Atmo and Vaisala) is for period ending a bit after 1:00 am this early morning. We had 0.47" here at house yesterday - most in morning around sunrise and then a bit more after dark.

Decided it would be interesting to show ALERT data for past 7 days, ending at 8:00 am this morning - quite a wet week for the greater metro area and surrounds. There are several sites with around 4 inches for the week!

This morning's 500 mb analysis (above from SPC) shows that center of western anticyclone, which is very elongated north to south, has shifted into Wyoming. Tucson's wind direction is out of sync with rest of observations, for some reason. IR image below is from 15 UTC and shows large MCS moving out over central GoC, leaving much of eastern portion of Arizona in the clear. Models suggest possibility of more early nighttime/morning showers in our area.

At bottom is GFS forecast for total precipitation during coming 7 days, ending at 5:00 pm on Monday the 26th - continued very wet for Arizona and western Mexico.