MESO: Mesoscale Discussion 1803

ACUS11 KWNS 062054
SWOMCD
SPC MCD 062053
SDZ000-062230-

MESOSCALE DISCUSSION 1803
NWS STORM PREDICTION CENTER NORMAN OK
0353 PM CDT THU AUG 06 2009

AREAS AFFECTED...PARTS OF WRN/CNTRL SD

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 062053Z - 062230Z

TRENDS ARE BEING MONITORED FOR AN INCREASING SEVERE THREAT AND THE
POSSIBILITY OF A WW. SUPERCELLS WITH THE POTENTIAL FOR LARGE
HAIL/LOCALIZED DAMAGING WIND GUSTS AND TORNADOES COULD DEVELOP AS
EARLY AS 22-00Z.

THE NORTHEASTWARD ADVECTION OF AN INCREASINGLY WARM AND CAPPING
ELEVATED MIXED LAYER OFF THE PLATEAU REGION INTO MUCH OF THE
NORTHERN AND CENTRAL PLAINS LATE THIS AFTERNOON AND EVENING IS A
COMPLICATING FACTOR CONCERNING SEVERE POTENTIAL. HOWEVER...THE
ENVIRONMENT ALONG AN EFFECTIVE WARM FRONT EAST AND SOUTHEAST OF THE
BLACK HILLS IS BECOMING MODERATE TO STRONGLY UNSTABLE WITH DAYTIME
HEATING. RUC GUIDANCE SUGGEST INHIBITION FOR MOIST BOUNDARY LAYER
PARCELS CHARACTERIZED BY MID/UPPER 60S SURFACE DEW POINTS HAS
WEAKENED...WITH CAPE NOW ON THE ORDER OF 2000-3000 J/KG. DEEP LAYER
SHEAR ACROSS THIS REGION IS STRONG BENEATH 30-40+ KT WESTERLY 500 MB
FLOW...AND LOW-LEVEL HODOGRAPHS ARE CYCLONICALLY CURVED AND QUITE
LARGE IN THE VICINITY OF A 40 KT SOUTHEASTERLY LOW-LEVEL JET...WHICH
IS PROGGED TO GRADUALLY VEER TO SOUTHERLY ACROSS WESTERN SOUTH
DAKOTA THROUGH EARLY EVENING. IT APPEARS ANOTHER MID-LEVEL IMPULSE
AND ASSOCIATED FORCING FOR UPWARD VERTICAL MOTION ARE IN THE PROCESS
OF PROGRESSING THROUGH THE CREST OF THE LARGER SCALE RIDGE ACROSS
THE REGION...WHICH COULD CONTRIBUTE TO THE DEVELOPMENT OF AT LEAST
SCATTERED SUPERCELLS BETWEEN THE BLACK HILLS AND THE PIERRE AREA OF
CENTRAL SOUTH DAKOTA BY 22-00Z.

..KERR.. 08/06/2009

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

ATTN...WFO...ABR...UNR...

LAT...LON 44460331 44950284 44940142 44680062 44080029 43560037
43190131 43540209 43710286 43960329 44460331

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