MESO: Mesoscale Discussion 1742

ACUS11 KWNS 211742
SWOMCD
SPC MCD 211741
IAZ000-MNZ000-211915-

MESOSCALE DISCUSSION 1742
NWS STORM PREDICTION CENTER NORMAN OK
1241 PM CDT WED AUG 21 2013

AREAS AFFECTED...NORTHERN IA/EXTREME SOUTHERN MN

CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY

VALID 211741Z - 211915Z

PROBABILITY OF WATCH ISSUANCE...20 PERCENT

SUMMARY...ISOLATED SEVERE TSTMS WITH HAIL/WIND WILL BE POSSIBLE
THROUGH EARLY/MID AFTERNOON ACROSS PORTIONS OF NORTHERN IA AND
PERHAPS EXTREME SOUTHERN MN...ALTHOUGH THE SHORT-TERM
EXTENT/MAGNITUDE OF THE SEVERE RISK IS A BIT UNCERTAIN. A MORE
CERTAIN/ORGANIZED SEVERE POTENTIAL IS EXPECTED TO EVOLVE LATER THIS
AFTERNOON/EARLY EVENING ACROSS A BROADER PORTION OF THE REGION.

DISCUSSION...A WEAK MID-LEVEL IMPULSE APPEARS TO BE EMBEDDED WITHIN
A RIBBON OF MODERATELY STRONG WESTERLIES ACROSS THE MIDDLE MO
VALLEY. THIS IS LIKELY A FACTOR TO A PERSISTENT MID-LEVEL CLOUD DECK
INTO SOUTHERN MN/NORTHERN IA...WITH A RECENT INCREASE IN A FEW TSTMS
ACROSS NORTHERN IA SINCE 1630Z. WITHIN THE WARM SECTOR JUST AHEAD OF
A SOUTHEAST-MOVING COLD FRONT...THESE STORMS MAY REMAIN A BIT
ELEVATED FOR THE TIME BEING. BUT EVEN SO...SUFFICIENTLY STEEP
MID-LEVEL LAPSE RATES/VERTICAL SHEAR WILL EXIST FOR AT LEAST A
PULSE-TYPE SEVERE HAIL/WIND POTENTIAL. GIVEN A WARMING BOUNDARY
LAYER NEAR/EAST OF THIS STORM DEVELOPMENT...TRENDS WILL CONTINUE TO
BE MONITORED FOR WHAT COULD BECOME MORE OF A CONSEQUENTIAL
SURFACE-BASED SEVERE THREAT INTO A MODERATELY-STRONGLY UNSTABLE
AIRMASS.

HOWEVER...OF MORE CERTAINTY WILL BE FOR SEVERE TSTM POTENTIAL TO
INCREASE ACROSS A BROADER PORTION OF THE REGION LATER THIS AFTERNOON
INTO EARLY EVENING OWING TO FRONTAL UPLIFT IN CONJUNCTION WITH A
DESTABILIZING PRE-FRONTAL BOUNDARY LAYER.

..GUYER/CORFIDI.. 08/21/2013

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

ATTN...WFO...DVN...ARX...MPX...DMX...FSD...

LAT...LON 42919492 43829504 43789310 43319179 42129209 42919492

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