MESO: Mesoscale Discussion 1789

ACUS11 KWNS 191353
SWOMCD
SPC MCD 191353
NCZ000-VAZ000-SCZ000-191530-

MESOSCALE DISCUSSION 1789
NWS STORM PREDICTION CENTER NORMAN OK
0853 AM CDT SUN AUG 19 2012

AREAS AFFECTED...THE CAROLINA AND SOUTHEAST VIRGINIA COASTAL PLAIN

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 191353Z - 191530Z

PROBABILITY OF WATCH ISSUANCE...60 PERCENT

SUMMARY...IT IS NOT CERTAIN THAT A WW WILL BE NEEDED...BUT TRENDS
ARE BEING MONITORED FOR THE POSSIBILITY OF AN INCREASING SEVERE
THREAT THAT COULD REQUIRE ONE LATE THIS MORNING OR EARLY THIS
AFTERNOON.

DISCUSSION...SEVERAL WEAK WAVES ARE EVIDENT ALONG A STALLED OR SLOW
MOVING SURFACE FRONT ROUGHLY EXTENDING ALONG THE I-95 CORRIDOR.
VARIABILITY IS HIGH AMONG THE MODELS CONCERNING THESE FEATURES...
BUT IT APPEARS THAT ONE UPPER IMPULSE IS ALREADY BEGINNING TO
RAPIDLY LIFT NORTHEAST OF THE SOUTHERN APPALACHIANS...WITH PERHAPS
ANOTHER WEAKER IMPULSE BEGINNING TO LIFT NORTHEAST OF THE EASTERN
GULF STATES.

SOUTHWESTERLY MID/UPPER FLOW IS MODERATELY STRONG NEAR THE
FRONT...ALONG WHICH CLUSTERS OF STORMS ARE GENERALLY
CONCENTRATED...AND THIS IS PROVIDING MORE THAN SUFFICIENT SHEAR FOR
MID-LEVEL UPDRAFT ROTATION AND ORGANIZED CONVECTION.
HOWEVER...LOW-LEVEL FLOW IS RATHER WEAK /20 KT OR LESS AT 850 MB/
AND NOT EXPECTED TO STRENGTHEN SUBSTANTIVELY. FURTHERMORE
MID-LEVELS ARE RELATIVELY WARM WITH WEAK LAPSE RATES...AND LOW-
LEVEL LAPSE RATES ARE NOT LIKELY TO STEEPEN SUBSTANTIALLY AHEAD OF
ACTIVITY. ON THE OTHER HAND...NEAR SURFACE AND DEEP LAYER MOISTURE
CONTENT IS HIGH...AND WILL CONTRIBUTE TO HEAVY PRECIPITATION LOADING
IN STRONGER CONVECTION.

IT CERTAINLY DOES NOT SEEM OUT OF THE QUESTION THAT AT LEAST
OCCASIONAL LOCALIZED STRONG SURFACE GUSTS WILL BE POSSIBLE WITH
SCATTERED EVOLVING STORM CLUSTERS...AS 25-30+ KT WEST SOUTHWESTERLY
DEEP LAYER MEAN FLOW ADVECTS THEM INTO AND ACROSS THE COASTAL PLAIN
THROUGH THE 15-18Z TIME FRAME. BUT...SEVERE POTENTIAL BEYOND
THAT...AT LEAST IN THE NEAR TERM...REMAINS A BIT UNCLEAR.

..KERR/MEAD.. 08/19/2012

...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...

ATTN...WFO...AKQ...MHX...RAH...ILM...CHS...CAE...

LAT...LON 32668002 33338038 34147977 35147854 35897755 36767694
36847595 35887546 35137563 33997723 33037900 32737960
32668002

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