Tuesday, October 04, 2011

First 500 mb Short Wave Coming Ashore This Morning

Showers and isolated thundershowers yesterday stayed mostly east and north of here as the Atmo WRF-GFS forecasts indicated. Across the ALERT network only 7 stations had rainfall past 24 hours and amounts were very light. Heaviest rainfall amounts (still all less than half an inch) fell at higher elevations far off to the northeast.

The first 500 mb short wave (mentioned in yesterday's post) is coming into southern California this morning and its associated cold front has advance to far western Arizona. This system has considrably more cloudiness with it (see 1445 UTC visible image below) than the models had been forecasting a couple odays ago. It appears that the surface front will advance across southern Arizona during the day, crossing the local area by evening. There will likely be showers along the front as per the new NAM forecasts this morning; however, the most substantial weather will again be over higher elevations to the north. Temperatures in middle levels remain quite cool (-12C and colder) so some thunderstorms are possible. Unfortunately, the early run of the WRF-GFS apparently crashed today. Regardless, it should be an interesting afternoon and evening.

 I will not worry much about the next, stronger system at this time. But, I do show below the NAM analysis at 250 mb for 1200 UTC this morning (top below). A very strong jetstream is crossing the Aleutians and diving southeastward across the northern Pacific. This jet will pull the next system southward, leading to a winter-like storm for the West. By midnight tonight (below bottom), the coming system has sharpened up along the Washington/Oregon coast, while the lead short wave is exiting southeastern Arizona.

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