MESO: Mesoscale Discussion 1259

ACUS11 KWNS 211733
SWOMCD
SPC MCD 211733
IAZ000-MNZ000-211900-

MESOSCALE DISCUSSION 1259
NWS STORM PREDICTION CENTER NORMAN OK
1233 PM CDT SUN JUN 21 2009

AREAS AFFECTED...NRN IA INTO SRN MN

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 211733Z - 211900Z

THE THREAT FOR SEVERE STORMS INCLUDING SUPERCELLS CAPABLE OF HAIL
AND TORNADOES IS EXPECTED TO INCREASE ACROSS DISCUSSION AREA THIS
AFTERNOON INTO EVENING. CONVECTIVE TRENDS ARE BEING MONITORED FOR A
POSSIBLE WW.

LATEST MESOANALYSIS INDICATED A SURFACE LOW BETWEEN MHE AND YKN WITH
ATTENDANT WARM FRONT EXTENDING SEWD THROUGH CNTRL IA /NEAR DSM/ INTO
W-CNTRL IL. A COLD FRONT TRAILED SWD FROM THE LOW THROUGH ERN NEB.
AS THIS LOW DEVELOPS EWD...EXPECT WARM FRONT TO PIVOT NWD TO
VICINITY OF THE IA/MN BORDER BY LATE AFTERNOON.

VISIBLE SATELLITE AND COMPOSITE RADAR DATA INDICATE DEEPENING
CUMULUS AHEAD OF SURFACE LOW AND COLD FRONT FROM FAR SERN SD SWD
INTO NERN NEB /NEAR OFK/. AMBIENT...WARM SECTOR AIR MASS IS WARMING
RAPIDLY AND WHEN COUPLED WITH DEWPOINTS OF 70-75 F...ENVIRONMENT HAS
BECOME MODERATELY UNSTABLE WITH MLCAPE OF 1000-2000 J/KG. BASED ON
THE ABSENCE OF ANY APPRECIABLE CAP PER 12Z OAX SOUNDING...EXPECT
CONVERGENCE ALONG SURFACE BOUNDARIES AND DEEPER ASCENT ALONG
TRAILING EXTENSION OF SHORT WAVE TROUGH LIFTING NEWD INTO THE UPPER
MS VALLEY TO FOSTER SCATTERED TSTM DEVELOPMENT BY MID AFTERNOON.

INITIAL STORM DEVELOPMENT IS EXPECTED TO OCCUR W/SW OF WARM FRONT
WITHIN REGION OF SUFFICIENT DEEP...BUT RELATIVELY WEAK LOW-LEVEL
SHEAR. AS SUCH...INITIAL SEVERE THREATS WILL BE HAIL AND PERHAPS
SOME WIND. THE POTENTIAL FOR TORNADOES IS EXPECTED TO INCREASE
LATER THIS AFTERNOON INTO EVENING AS MORE MATURE STORMS /SUPERCELLS/
BEGIN TO INTERACT WITH WARM FRONT WHERE AIR MASS WILL CONTINUE TO
DESTABILIZE AND LOW-LEVEL SHEAR INCREASE.

..MEAD.. 06/21/2009

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

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

LAT...LON 42679608 43169630 43569608 43739503 43659335 43199181
42709141 42259139 42059164 42019281 42119407 42339539
42679608

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