Saturday, June 25, 2011

More Meteorological Miscellany

High temperature reached 107F again yesterday afternoon at NWS TUS. During the middle to late afternoon there were actually cumulus clouds visible down to the south of Tucson, along with some towering cumulus off to the far southeast, in the Borderlands. I note this morning that the blistering heat continues to deepen the heat low in the lower Colorado River Basin - with 24-hour pressure falls this morning of 1.5 to 2.0 mb common over southern and western Arizona. Largest fall I noticed in Arizona was 2.1 mb at Nogales.

The two images above show blended PW over the eastern Pacific - the top image is from 1200 UTC on 23 June and the bottom is image is from 1200 UTC this morning (Saturday 25 June 2011). It appears that even though Beatriz was short-lived, the storm's remnants have helped push a large mass of moist, lower-level air both up the GoC and also to the west of Baja. This has been quite a substantial development - some areas west of Baja, and north of 20 degrees N, have experienced a 48-hour increase in PW of around 45 mm! If this great blob of moisture continues its northwestward push for the next couple of days, it will be well-positioned to interact with a deepening 500 mg trough forecast to dig southward off the west coast.
The two images below are the 120-hour forecast of the GFS operational member for 500 mb and the surface - valid time is 5 pm MST next Wednesday afternoon. The model forecast indicates the 500 mb short-wave to be inland, crossing the Great Basin and butting heads with the large central US anticyclone. The model forecasts moisture to be pulled northward from low latitudes as the two features (one spring-like and one definitely summer-like) interact. This interaction brings the first chance for summer-season storms into parts of Arizona. The model indicates that the forecast storms are developing within moisture pulled north from the GoC and from the remnants of Sierra Madre Occidental diurnal thunderstorms. Thus, the possible role of the moisture push discussed above is not obvious yet in the model forecasts.
Note - see Jim Steenburgh's blog for a discussion of the deepening west coast trough-

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