Another dilemma re subtropics and westerlies

I have taken a quick look at some of the charts and model progs this morning.

First, the morning Tucson sounding has dried some and indicates that CAPE will likely be not very great today and that what there is should develop only over the mountains. So another quiet day is likely locally here in the Tucson metro area. The sounding (Fig. 1) shows a nice example of why the LI computed at 500 mb out here can be very deceptive!

Second, an infrared satellite image at 1230 UTC this morning (Fig. 2) shows a large area of storms and disturbed weather over and south of the southern end of the GoC. The question is what is this and will it affect our weather up here in Arizona? The only sounding available this morning near to this area is Mazatlan, which indicates a very moist and unstable air mass with low level-easterly winds. The nam and gfs models forecast a strenthening cyclone at 850 mb down in this region; however, as per usual this summer, the models have very different details in their forecasts.

I'll illustrate this with the 850 mb 42-h forecasts from the nam and gfs. The nam (Fig. 3 - left) indicates a low center SW of Baja with strong southerly winds intruding far north into northwestern Arizona, i.e., a significant surge of moisture into the lower Colorado River Basin. However, the gfs (Fig. 4 - right) predicts a cyclone over the southern GoC that is totally separated from the circulation fields further north over northern Sonora and the U.S. Southwest; i.e., no hint of a moisture surge into the U.S.

The weather in Arizona the nextcouple of days will, of course, depend upon which model's forecast is closest to what happens in the real atmosphere. Both models forecast several weak short-waves at 500 mb moving across Arziona and interacting either with increased moisture (nam with significant storms and rainfall) or residual moisture (gfs with isolated and mountain storms). I guess that I'd tend toward the gfs forecasts, given the two models' performance during Hurricane John.