SPC MD 1544


MD 1544 Image

Mesoscale Discussion 1544
NWS Storm Prediction Center Norman OK
1046 PM CDT Fri Aug 21 2020

Areas affected...Parts of southern Arizona

Concerning...Severe potential...Watch unlikely 

Valid 220346Z - 220615Z

Probability of Watch Issuance...5 percent

SUMMARY...Strong thunderstorm generated wind gusts may impact
portions of Santa Cruz and Pima counties by Midnight-2 AM MST.

DISCUSSION...Deep-layer ambient mean flow beneath upper ridging is
generally light and variable near the Arizona/Sonora vicinity. 
However, easterly/southeasterly flow at mid-levels (centered around
500 mb) appears to be contributing to a west-northwesterly
propagation of vigorous thunderstorm development off the higher
terrain of northern Sonora.  This is now generally focused along a
conglomerate, convectively generated surface cold pool, which may be
maintained several more hours as inflow of moist air characterized
by large CAPE (perhaps up to 4000 J/kg) continues.  

While cooler and more stable boundary-layer air is maintained 
across much of southeastern Arizona, stronger thunderstorm
development seems likely to remain focused south of the
international border, across northern Sonora.  However, a
northwestward surge of the cold pool and associated vigorous
thunderstorm development is possible late this evening, toward
portions of south central Arizona, where the remnants of a hot,
moist and deeply-mixed daytime boundary layer, may contribute to the
potential for strong surface gusts.

..Kerr/Edwards.. 08/22/2020

...Please see www.spc.noaa.gov for graphic product...


LAT...LON   31401079 31230948 30961006 30411032 30181104 31491229
            31901165 31401079 

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