Significant Outflows Yesterday Evening

There was another increase in thunderstorm activity yesterday - primarily at higher elevations and to the southwest of Tucson. The storms over southern Arizona and Sonora consolidated into a large MCS that moved west-southwestward over the northern GoC (see 10 pm MST water vapor image above). Outflows from this convective system moved across most of southern Arizona and surged rapidly northward along the Colorado River. The outflows reached to the Phoenix area, where there was wind and dust and some light showers. However, the outflows have increased PW across all of southern Arizona. The ALERT network had 65 sites with rainfall during past 24-hours (about 70% areal coverage). Amounts tended to be light, with only 6 stations having more than half an inch and 1 station to the southwest recorded just over an inch. Here at the house we had 0.53" as several thunderstorms drifted south from the Catalinas directly over our location. We had outflows from the north initially, and then strong outflows from the south around 8 to 9 pm - max gusts probably around 40 mph.

The GPS time-series of PW at U of A (above) shows the steady increase of PW this week with values now around an inch and a half. The visible satellite image at 7 am MST (below) shows a large mass of debris cloud covering western Mexico and much of southern Arizona. There appears to be a substantial vorticity maximum embedded in the cloud mass near the northern GoC.

The experimental, blended PW from CIRA (above at 6 am MST) shows that the larger-scale circulation associated with TS Hector has pushed very high PW about half way up the GoC. The extensions of higher PW (greens > 25 mm and yellows < 50 mm) into northern Sonora and Arizona have been generated by the convective outflows of the last two days - a nice example of the role of MCSs in pushing moisture northward due to cool, moist outflows.

This morning's Tucson sounding (skewT plot for 12Z above) shows deep moisture and a fair amount of CAPE. The winds aloft remain somewhat chopped up, but there appears to be steering flow from the east to southeast of about 20 kts in the 600 to 300 mb layer. It appears that the string of 100+ days has finally ended. Both the early WRF-GFS and the new NAM indicate storms over most of Pima County this afternoon, but again the models forecast the heaviest activity to occur from south to west of Tucson. This is a day to check the 12 UTC forecasts from Atmo's WRF model, as the forecast situation is quite complex.