Friday, July 17, 2009

Brief Outlook for Today - Friday July 17, 2009

I posted a long message below about yesterday – important event because bad RRS sounding clearly led the NWS astray on the short term forecast for the storms approaching the metro area.

As for today, it appears that most ingredients for a big severe storm day are, or will be by late afternoon, in place, except for the continuing and distressing shortage of low-level moisture. I can finagle a sounding modification that gives us similar CAPE to yesterday – perhaps a tad better.

The 500 mb anticyclone is over Arizona/Utah border and elongated SE to NW. Very good steering flow and shear profiles by afternoon. Cool middle level air coming around the 500 anticyclone. Not obvious exactly where weak 500 S/W might be, but NAM initialization appears a bit suspect, acerbated by missing winds at Guaymas. The weak inverted trough at 700 mb is clearly east of here and visible satellite loop indicates 500 mb S/W may be also.

One possible complication is the large mass of cloud and some convection over northern Mexico and borderlands of southeast Arizona. This could limit heating to some degree and possibly get too much convection going too early. But it should be another interesting day.

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