More showers yesterday across much of southern Arizona as the 500 mb vorticity maxima drifted back toward east and northeast. Rainfall was widespread during past 24-hours (about 80% coverage at gauges in southeast Arizona) but amounts were generally light (less than a quarter of an inch). The four stations I found with more than half an inch were: Arivaca with 0.94"; Carr with 0.66"; Sasabe with 0.65"; and Florida Canyon with 0.55".-----------------------------------------------
The morning Tucson sounding (top graphic) indicates southwesterly winds at all levels except near the surface. Winds are weak below 300 mb and stronger and more westerly above. Not a good vertical wind profile for many locations. So, while the NAM morning forecast indicates a nice rain event for southeast Arizona through midnight, I'm not optimistic for the house, unless a storm builds right overhead. The sounding is considerably too moist (4 to 6 mm wrt to GPS observations) and PW has been trending downward across southern Arizona during the night. However, the presence of convective clouds west to near the Colorado River certainly indicates the presence of CAPE. Middle level temperatures are the coolest they've been in several weeks, which is a help - hopefully the warmer temps out along west coast will be shunted off to the southwest. Lots of clear skies to the southwest of Tucson, so there'll be much more sunshine today. Thus, today a good chance for storms, especially in locales favored by the southwesterly wind profile.
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The NAM 500 mb forecast valid at midnight is shown in middle graphic. While Frank is getting a bit far to the west, the pronounced inverted trough to Frank's northeast should help keep an influx of deeper moisture moving northward. The deep 500 mb trough forecast to dig into the west coast on the weekend will probably work in concert with Frank to increase southerly winds. So while tomorrow is uncertain wrt to moisture and CAPE, Sunday appears to have significant potential for strong storms. The shear profile will be a central US variety with strong and veering winds - so a good possibility for a transition type day with more classic severe thunderstorms. Note also that both the westerlies and the tropics are very active - so, since we're in the middle, it's hard to tell very far ahead which features will affect us the most - meaning a wary weather watch is prudent through the weekend.
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The bottom graphic is the NHC forecast for Frank, indicating that its remnants will move back toward Baja next Monday and Tuesday. That's too far out to know for sure how the Fall-like west coast trough will have behaved - some long-range models minor it out quickly, but we'll have to wait and see what transpires over the weekend.
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