Friday, July 28, 2017

Some Rain Last Night Plus Miscellaney

Yesterday was mostly anvils here in metro area with strongest storms to our east. However a strong outflow moved across low-elevations between 7:00 to 8:00 pm MST, with a few rumbles of thunder and light showers into early morning hours. The ALERT plot above is for 24-hours ending at 7:00 am this morning. Here at house there was 0.08". Rain amounts at several RAWS sites to our east were right around 1 inch. Guthrie reported a gust to 74 mph during the storms - accurate?

The 00 UTC sounding from TWC below had slight CAPE and a wind profile continuing to support anvil spread to west from storms.

This morning's TWC sounding has changed significantly, partly due to storms and partly due to  an anticyclone shift some to north and west. The wind profile (above) shows a shear profile above afternoon cloud base that is very favorable for organized and possibly severe thunderstorms, and much faster movement toward west. However, considerable heating will be needed.

The morning 500 mb analysis (from NCAR, below) shows a bean-shaped anticyclone centered around the Four Corners and a distinct inverted trough that's nearly overhead. This morning's NAM forecasts move this feature very slowly during next 24-hours while keeping it very active.

The 7:00 am visible satellite image - second below - shows heavy cloud cover over most of state, except for southeastern Arizona - certainly appears favorable for sunshine and good heating.

Finally, considerable MCS activity moved over the middle and upper GoC last night and early this morning - above is IR image from midnight. This seems to have led to a significant moisture surge at Yuma early this morning with a temperature drop, dewpoints increasing from 50s into 70s, and strong south to southeast winds. The early morning VAD wind profiles from Yuma radar indicate strong winds up to 6,000 ft above the radar. Think this may be the first surge profile this deep and strong so far this summer.

Thursday, July 27, 2017

What's Wrong With NWS "Happening Now?"

The NWS often posts a "Happening Now" graphic on their web page, as per above. The problem with these is that convective storms both develop and dissipate rapidly. The graphic above was still "live" on the NWS page at 4:45 pm MST this afternoon. Compare with the TUS composite radar (below) from 4:14 pm.

Conflicting Signals This Morning

Thunderstorms and light showers returned to high elevations in the Catalinas yesterday - ALERT data above for 24-hours ending at 7:00 am MST this morning.

The morning sounding (below from SPC) indicates decent CAPE if the BL mixes well to a bit above 700 mb - which would require a high at airport of around 104 F. The wind profile however is not very favorable and would tend to bring anvils over city, keeping the temperature down a bit.

The 06 UTC WRF-GFS from Atmo forecasts just sprinkles for the metro area through midnight (above). The forecast sounding for TWC at mid-afternoon requires some outflow lift to produce thunderstorms. The winds at high-levels increase some and become more easterly, increasing the threat of anvils over the city. However, the surface plot forecast for 5:00 pm this afternoon (below) indicates a strong outflow from southeast moving across city. The model forecasts decent heating until about 2:00 pm before anvils increase over low-elevations. So mixed signals for this afternoon and another wait to see day.

The IR image at bottom is from 07 UTC last night. There was significant thunderstorm activity over the middle and south end of the GoC last night and this may begin pushing extremely moist mT air north again.

Wednesday, July 26, 2017

Downturn Miscellany

Little to report this morning. Closest storm and rainfall activity moved from Sonora up over the Huachucas early evening and have hung around the mountains all night. Totally down across Pima County.

The 13 UTC MIMIC total PW (above) shows PW holding around 1.5" across southern Arizona while very high values reach north to around Guaymas and Hermosillo. Hurricane Hilary is at about 16N, south of Baja. 

The Rillito at Dodge USGS stream-flow gauge (below) showed three distinct peaks during the past week, with one on Thursday evening nearly reaching 5,000 cfs. 

The morning NHC forecast for Hilary is shown above and keeps the storm far west of south tip of Baja. However, the operational version of the GFS turns the storm northward. This is indicated in the 00 UTC WRF-GFS forecast of 850 mb winds and PW below. Compare the forecast locations of the storm for next Monday morning (the 31st).

Tuesday, July 25, 2017

Downturn Continues

Models were very good yesterday in forecasting the downturn to continue. Much different picture yesterday for detected CGs above (from Atmo and Vaisala) for 24-hours ending at 6:00 am MST this morning, as thunderstorm activity was much reduced. Precipitation for same period (below from ALERT) across metro area was focused around the airport - TUS reported 0.49" while we had just 0.01 here from light afternoon sprinkles.

The morning TWC sounding (above) remains very moist and continues with some CAPE as the BL mixes more deeply this afternoon. However, nearly unidirectional wind profile means anvils heading out ahead of any mountain storms that would develop, hindering their advance toward lower elevations. Warm temperatures continue in middle levels.

The WRF-GFS from midnight run last night (below - valid through 6:00 am tomorrow morning)) forecasts little rainfall over southern Arizona, as the downturn continues.

The trough off California does not shift further south, and PW remains high, which is good for a return to better conditions as the 500 high builds again and shifts back to Four Corners/Great Basin region. The GEFS 500 mb spaghetti plot at bottom shows the longer term adjustments to large-scale pattern (valid at 216 hours - 00 UTC on August 3rd).

Monday, July 24, 2017

Models Forecast Continuing Downturn In Storm Activity

Although I meant to post a daily outlook yesterday, I was delayed by trimming trees for special pick-up today and then by the amazing final 9 holes of the British Open. So, I never got around to it.

Detected CG flashes above (from Atmo and Vaisala) show an expected donut hole over the metro area after such a large event the day before, as well as a definite decrease in thunderstorm activity across southeastern Arizona.

Was very dreary day here with overcast skies, a few rumbles of thunder from the Catalina Foothills, and occasional spits and light showers of rain - total for day and night here was 0.08".

The ALERT plot below is for 24-hours ending at 7:30 am MST - another 100% areal coverage day but with low elevation amounts quite light. Four mountain sites had another day with over an inch of rain.

The amazingly moist pool of PW over southern Arizona (as per 12 UTC TWC sounding plot above) is forecast to shift northward as winds continue more southerly. Although low-levels remain quite moist, the WRF-GFS from 06 UTC last night indicates a serious downturn in storm activity across southern Arizona next several days - I assume that this is mostly due to the very warm (hot) middle-level temperatures. The visible satellite image below is from 7:00 am - storms to our northwest underway, but with a large region of Sonora being clear and presumable drier. Some sunshine would be nice after several mostly cloudy days.

Sunday, July 23, 2017

Brief Overview - Yesterday's Heavy Storms

Outflows from storms to south and line of storms moving into Catalinas from the northeast, collided over or near the mountains, and new storms were developing by 5:00 pm MST - above. By 7:30 pm mountains were becoming visible as serious street flooding was affecting north-central Tucson. We were on the east side near Kolb and 22nd and headed home about 6:50 pm - this is about a 25 minute drive usually. We were stranded at the intersection of Tucson and Glenn about 7:30 pm, when I took the photo below. Tucson was flowing as if it were a wash and cars were stalled in all directions in the high water. It took us more than an hour and a half before we zigged back and forth to avoid the worst flooding and got home. Quite a trip.

The map below shows ALERT network rainfall for 24-hours ending at 6:00 am this morning - essentially 100% coverage again - with three sites along west side of network having 0.04" or less. There were 13 sites reporting more than an inch. Here at the house I found 1.40" in the gauge once we got back.

This gives us 5.46" for July - second highest July amount since we've been here. Wettest July was in 1999 with 6.63".

Found three RAWS sites in southeast Arizona with more than an inch and also noted gusts to 68 mph up at Prescott and 52 mph at Safford. Quite an afternoon and evening!

Saturday, July 22, 2017

Reduced Activity Yesterday - Pattern Remains Stagnant

Storm developed along the foothills north of here a bit before 7:00 pm MST (above), but could not come into this part of town. The storm seemed to shift southeastward and dissipate. Here at house we had thunder and a couple of spits of rain.

Plot below is of detected CG flashes for 24-hours ending at 1:00 am today, and shows considerably less activity over eastern Pima County than occurred yesterday (from Atmo and Vaisala).

These two plots show 24-hour precipitation ending at 7:00 am this morning. Basically a metro donut hole, but with storms coming off the Rincons and developing into a line that moved southward away from the City. Plot above is from ALERT network and plot below is from MesoWest.

The 12 UTC 500 mb analysis above is from NCAR and shows several things of interest: western lobe of anticyclone is again over the Great Basin; height gradients over much of western and central U.S. are extremely weak; I count five inverted troughs from Louisiana to southern California; Huge data void remains over all of northern half of Mexico. The troughs are very weak and moving slowly, if at all. Their main role seems to be in determining local steering flows for storms that do develop.

The TWC sounding (below) this morning is little changed from yesterday and thus it looks like another wait and watch day.

I did look briefly at the 06 UTC forecasts from the WRF model run at Atmo. Both versions had a significant area of storms forecast to our northeast around sunrise and so I didn't look further. Perhaps the 12 UTC runs will start off better - check the new runs and Mike"s morning discussion.

Friday, July 21, 2017

Widespread Storms And Rain Yesterday Evening

Kitt Peak view to the north at 4:41 pm MST yesterday afternoon. View from campus to the north at 5:00 pm shows rain shower over the mountains with its outflow apparently producing  a nearly circular arc of new updraft clouds. The storm moved into the foothills producing heavy rains and there were several more redevelopments as the outflows spread south across the metro area. Only 0.24" here at house with this event.

ALERT network precipitation through 6:30 am this morning (below) shows 100% over the metro area with 11 sites measuring over an inch. Quite some event given the light and variable wind profile that prevailed yesterday.

This morning's sounding plot (above) continues to show light winds aloft but with a more systematic direction profile backing from north-northeast at 700 mb to westerly at 200 mb. Moisture and CAPE continue high, but some drying is occurring in upper troposphere. The visible image below seems to indicate sunshine this morning. The 500 analysis for 12 UTC at bottom indicates weak IT and cyclone at 500 mb approaching slowly from the east. Storms again on mountains today but with  light steering toward the south. Perhaps a repeat, but we'll have to watch how things evolve today.

Thursday, July 20, 2017

Uncertain Day Today - Downburst Near University Yesterday

Edited to add: Art Rangno reported 3.36 inches of rain yesterday at his place in Catalina. His approximate location is shown in map below.

Plot above shows detected CG flashes for past 24-hours ending at 6:00 am MST - from Atmo and Vaisala. Cluster of green flashes Tucson area was with the down burst storm that hit university area a bit before my afternoon post yesterday. Note the time bar that indicates the mid-afternoon storms were all that impacted metro area. Widespread rains with heaviest near downtown and in the Catalinas ALERT below is for 24-hours ending at 7:00 am. Quite a few reports of trees down with this storm - reports for yesterday from SPC is second below.

The upper-level IT that was near El Paso yesterday has elongated northwestward and is being pulled apart as it circles around the central US anticyclone - water vapor image above from 5:15 am this morning.

The morning TWC sounding (above) remains wet and unstable, particularly for the mountains. However, winds through the troposphere are essentially light and variable. Mountain storms may drift anywhere - following outflows and most unstable air. Widespread debris cloudiness over Arizona and northern Mexico at 6:45 am (visible image below) means uncertain heating. This seems to be a day where we just sit and watch what evolves.