Thursday, July 21, 2016

Play It Again

There was considerably less thunderstorm activity over much of Arizona yesterday versus that on Tuesday. For example, only 15% of the ALERT sites in eastern Pima County recorded precipitation yesterday, while 60% of the sites had rainfall on Tuesday. Amounts were quite light both days. Here at the house there was an early afternoon thunderstorm from a small cell to our south - but no rainfall.

With a bit more than a week left in July, we need a decent storm or this will be driest July here since I started my records.

This morning's skewT plot for TWC continues very similar to past several mornings. However, winds in mid-levels are southerly at 15 to 20 kts and winds above that are a bit chopped and have similar speeds - so anvil shading may not spread ahead of storm cells. Further, mid-level temperatures have cooled a bit, and with no mid-level inversion, thunderstorms should develop late morning over the mountains. What happens then? - we'll just have to watch. Several cells did form at low elevations yesterday - and getting a cell developing just to our south will provide the best chance for rain here.

There was apparently no 06 UTC run of the WRF-NAM. The WRF-GFS forecast for TWC skewT valid at 2 pm is shown above. Forecast wind profile is uni-directional from the south-southeast and model has mixed boundary layer out to 600 mb - perhaps a greater threat of downburst winds today. Although the model calculations indicate CAPE at 1400+, a more realistic estimate gives about 750 J/kg. 

The model forecast for 500 mb valid at noon today (below) shows the wide band of cooler air over eastern Arizona, as well as a very distinct anticyclone center east-northeast of El Paso.

The WRF-GFS forecast of composite radar echoes above is valid at 4:00 pm MST indicates a very stormy afternoon over eastern Pima County. However, the GFS version of the model has tended to overdo storms recently. The NAM version from 00 UTC last evening is much more subdued - so again we'll have to watch how things go later this morning.

The eastern Pacific continues very active, and there is a bit of longer-term hope in this morning's NHC outlook (below). The system that could become Georgette is forecast to head much closer to Baja than past storms - providing some possiblities for a serious GoC surge by early next week.

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