Sunday, July 19, 2009

Brief Summary Yesterday/Outlook Today

Yesterday was essentially a down day in most of southeast Arizona with some isolated, high base storms. There were 5 of 93 stations (foothills of Catalinas and Rincons) in the ALERT network which had very light amounts of rain during the late afternoon and none with rain during the night (0.08” at one station). A cell near Casa Grande produced a report of wind damage and dust blew in over Phoenix from the south, reducing visibility at Sky Harbor to as little as a quarter mile. The most intense storms of the day developed over the rugged terrain of the Tohono O’odham Nation during late morning. These intensified and move rapidly westward, apparently ahead of a S/W at 500 mb. These storms (see 2245z satellite image above) reached Yuma around 4 pm producing a serious dust storm, wind damage and measured gusts to 54 mph at the airport. Yuma also reported 0.10” of rain, so mud is probably splattered over everything out there this morning. I couldn’t find a good image to grab, but there are several videos of the event up on the internet.

An MCS that decayed over the central GoC may produce a shallow surge today, but it probably won’t be significant enough to change the thermodynamics much. This morning’s TWC sounding indicates that yesterday’s residual boundary layer has 6.5 g/kg mixing ratio. This value produces a lifted parcel that hits saturation at about 570 mb with theta-w of about 20.5C – really quite low for late July. Moistening during day could perhaps yield a low-elevation, lifted parcel with theta-w of 22C and a small wedge of CAPE between 500 and 300 mb.

Precipitable water values are around an inch to an inch and a quarter (a bit higher after the local moistening out around Yuma). Yesterday evening’s TWC sounding exhibited the common hot/dry problem of the RRS sondes and was about 0.3” too dry.

The 500 mb anticyclone is centered over the White Mountains and is progged to shift slightly southward toward Wilcox during the day. Thus, it appears that it will be another very hot day of isolated, high-based storms that will have excellent microburst/downburst potential. I will have to be watering some of the plants this evening – which again is not so typical in late July.

However, the S/W that produced the Yuma storms will likely bring some excitement to the mountains and interior of southern California.

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