MESO: Mesoscale Discussion 2275

ACUS11 KWNS 222221
SWOMCD
SPC MCD 222221
SDZ000-NEZ000-WYZ000-222345-

MESOSCALE DISCUSSION 2275
NWS STORM PREDICTION CENTER NORMAN OK
0521 PM CDT MON SEP 22 2008

AREAS AFFECTED...PARTS OF WRN NEB INTO W CNTRL SD

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 222221Z - 222345Z

TRENDS ARE BEING MONITORED FOR AN INCREASING SEVERE THREAT AND THE
POSSIBILITY OF A WW.

BENEATH STEEP MID-LEVEL LAPSE RATES ASSOCIATED WITH AN ELEVATED
MIXED LAYER ADVECTING NORTHEAST OF THE CENTRAL ROCKIES...THE
BOUNDARY LAYER HAS BECOME FAIRLY DEEPLY MIXED AND POTENTIALLY
UNSTABLE WITH CAPE ON THE ORDER OF 1000-2000 J/KG ACROSS MUCH OF THE
NEBRASKA PANHANDLE INTO WEST CENTRAL SOUTH DAKOTA. THIS ENVIRONMENT
HAS EVOLVED ALONG AND SOUTH OF A SURFACE FRONTAL ZONE WHICH HAS
TEMPORARILY STALLED NEAR THE WYOMING/NEBRASKA BORDER INTO AREAS
WEST/NORTHWEST OF PHILIP AND MOBRIDGE SOUTH DAKOTA.
BUT...OBSERVATIONAL AND MODEL FORECAST DATA SUGGEST THAT THIS FRONT
WILL BEGIN TO SURGE EASTWARD OUT OF SOUTHEAST WYOMING BY
23/00-03Z...IN THE WAKE OF A DEVELOPING WEAK SURFACE WAVE ACROSS
NORTHWEST NEBRASKA INTO CENTRAL SOUTH DAKOTA. THIS IS EXPECTED IN
RESPONSE TO FORCING ASSOCIATED WITH A SIGNIFICANT SHORT WAVE IMPULSE
NOW ACCELERATING NORTHEASTWARD OUT OF THE EASTERN GREAT BASIN.

WHILE IT APPEARS THE BULK OF CONVECTIVE DEVELOPMENT LATER THIS
EVENING INTO THE OVERNIGHT HOURS MAY BE POST-FRONTAL...A WINDOW OF
OPPORTUNITY APPEARS TO EXIST FOR PRE-FRONTAL BOUNDARY LAYER BASED
STORMS LATE THIS AFTERNOON INTO THE MID-EVENING HOURS. IF THIS
OCCURS...DEEP LAYER SHEAR BENEATH 30-50 KT SOUTHWESTERLY MID-LEVEL
FLOW WILL BE SUFFICIENT FOR SUPERCELLS. IN ADDITION TO THE RISK FOR
LARGE HAIL...DAMAGING WIND GUSTS WILL BE POSSIBLE UNTIL BOUNDARY
LAYER STABILIZATION OCCURS...ASSOCIATED WITH THE ONSET OF
RADIATIONAL COOLING AND FRONTAL PASSAGE LATER THIS EVENING.

..KERR.. 09/22/2008

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

ATTN...WFO...ABR...LBF...UNR...CYS...

41770388 42560405 43260379 44250245 45500139 45660070
45490010 44999970 44109985 43250074 42840120 42020196
41490304

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