Monday, September 20, 2010

MESO: Mesoscale Discussion 1867

ACUS11 KWNS 210041
SWOMCD
SPC MCD 210040
MNZ000-WIZ000-210245-

MESOSCALE DISCUSSION 1867
NWS STORM PREDICTION CENTER NORMAN OK
0740 PM CDT MON SEP 20 2010

AREAS AFFECTED...PORTIONS CENTRAL-NERN MN...NWRN WI...WRN LS.

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 210040Z - 210245Z

SHALLOW/ELEVATED CONVECTION WITH ISOLATED LTG...NOW DEVELOPING
ACROSS PORTIONS W-CENTRAL/NWRN MN...MAY INCREASE IN
COVERAGE/INTENSITY THROUGH AT LEAST 03Z AND BACKBUILD SWWD TOWARD
MN/SD BORDER REGION. MAIN THREAT N OF WARM FRONT WILL BE HAIL.
STG-SVR GUSTS ALSO WILL BE POSSIBLE WITH ANY OF THIS ACTIVITY THAT
CAN DEVELOP ALONG OR S OF WARM FRONT. NEARLY SFC-BASED SUPERCELL
MAY EVOLVE FROM ANY RELATIVELY DISCRETE/TAIL-END CONVECTION NEAR
WARM FRONT...HOWEVER THIS REPRESENTS A LOW-PROBABILITY...CONDITIONAL
AND SPATIALLY LIMITED SCENARIO AMIDST PREDOMINANTLY LINEAR OR
SEGMENTED CONVECTIVE REGIME.

AT 00Z...SFC MESOANALYSIS REVEALED TRIPLE-POINT LOW OVER W-CENTRAL
MN NEAR GRANT COUNTY...COLD FRONT SWWD ACROSS SD/NEB NEAR
MHE-ANW-SNY LINE. WARM FRONT WAS DRAWN FROM LOW SEWD ACROSS MSP
AREA...TO NEAR RFD. STRONGEST LOW-LEVEL SHEAR WILL REMAIN ALONG AND
N OF WARM FRONT WHERE NEAR-SFC WINDS ARE RELATIVELY BACKED.
HOWEVER...PERSISTENT/STRATIFORM CLOUD COVER HAS KEPT AIR MASS VERY
STABLE N OF WARM FRONT WITH SFC DEW TEMPS 50S TO LOW 60S F. WARM
FRONT IS EXPECTED TO MOVE NEWD ABOUT 10 KT WHILE BEING OVERTAKEN BY
COLD FRONT MOVING EWD TO SEWD 15-20 KT. 00Z MPX SOUNDING WAS TAKEN
ALONG MOIST AXIS IN WARM FRONTAL ZONE...WHERE BOUNDARY-LAYER STATIC
STABILITY WAS CONSIDERABLY STRONGER TO N AND MOISTURE WEAKER TO S.
AS SUCH...THAT RAOB FORTUITOUSLY SAMPLED STRONGEST-CASE SCENARIO FOR
SFC-BASED PARCELS OVER REGION. MOST CONVECTION SHOULD OCCUR AS
PARCELS ARE BOOSTED ISENTROPICALLY TO LFC IN VERY STG WAA REGIME N
OF WARM FRONT...AMIDST 50-65 KT SWLY LLJ. SOURCE REGION FOR
ELEVATED PARCELS N OF WARM FRONT ORIGINATES IN SFC-850 MB
ENVIRONMENT OF CENTRAL PLAINS AND SRN HIGH PLAINS...NOT QUITE AS
HIGH IN THETAE AS PARCELS NOW ALONG WARM FRONT OVER SERN MN.
STILL...THAT SHOULD BE SUFFICIENT TO SUPPORT MUCAPE AROUND 2000
J/KG...IN TANDEM WITH STRENGTHENING LAPSE RATES ALOFT AHEAD OF UPPER
PERTURBATION OVER DAKOTAS. MODIFIED RAOB AND RUC SOUNDINGS SUGGEST
FAVORABLE EFFECTIVE SHEAR FOR STORM ORGANIZATION...RANGING FROM
30-50 KT AND STRONGLY DEPENDENT ON DEPTH/POSITION OF CAPE LAYER
WITHIN VERTICAL WIND PROFILES.

..EDWARDS.. 09/21/2010

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

ATTN...WFO...DLH...MPX...FGF...

LAT...LON 48048992 47719013 46719085 45699197 45289327 45369454
45739546 46239535 47119443 48119383 48519348 48629335
48639308 48509261 48449275 48449252 48239232 48349226
48349203 48229196 48199174 48039158 48079125 48309084
48089076 48139013 48048992

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