Beautiful Fall-Like Morning in Tucson (9 August 2009)

It was a crisp and very sparkling morning here at the house. I didn’t check the thermometer until 6:30 am and it was then at 64F – may have been lower. I see some stations away from the city were in the 50s. Unfortunately, we now have had 3 more consecutive days with no rainfall across the Pima County ALERT network.

Not much more to say about current conditions. Precipitable water amounts are less than half an inch across the state except for the far southeast where amounts are hanging in there at three quarters of an inch.

The morning upper-air charts show a large, inverted trough in the easterlies (present from 200 mb down to 700 mb that arcs from Arkansas to the region near and south of the southern end of the Gulf of California). This feature is butting heads with the unusually deep trough in the westerlies that is affecting all of the US west of 100W. Looks like the inverted trough in easterlies will shear apart – with a portion in lower troposphere moving out into the Pacific (see below re model TS development) and the portion from Texas to Arkansas pulling away to the northeast – leaving a weak trough over Mexico. There is 700 mb cool advection into the lower Gulf of California which will keep pressures relatively high down there, perhaps pushing more moist low-level air toward southern Arizona.

The NAM forecasts this morning indicate several interesting developments by Tuesday and Wednesday. The model spins-up a new Tropical Storm southwest of Baja. It also appears to consolidate the remnant inverted trough over central Mexico and swings that strengthened feature northwestward across western Mexico and into Arizona by Wednesday afternoon. While this is happening, the model shifts the western center of the subtropical anticyclone northward toward the Four Corners region. If the events depicted in the model forecast actually transpire, we would see a significant low-level surge of GoC moisture into southern Arizona as early as Tuesday morning leading to a return of thunderstorm activity.

So, there are some things that we should keep an eye on as the new week gets underway.