MESO: Mesoscale Discussion 1279

ACUS11 KWNS 252100
SWOMCD
SPC MCD 252059
NDZ000-SDZ000-WYZ000-252230-

MESOSCALE DISCUSSION 1279
NWS STORM PREDICTION CENTER NORMAN OK
0359 PM CDT MON JUN 25 2007

AREAS AFFECTED...PARTS OF NE WY THRU MUCH OF THE DAKOTAS

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 252059Z - 252230Z

TRENDS ARE BEING MONITORED FOR AN INCREASING SEVERE THREAT. ONE OR
MORE WWS WILL LIKELY BE NEEDED...BUT SOME UNCERTAINTY EXISTS
CONCERNING HOW SOON.

STRONG HEATING IN NARROW PRE-FRONTAL THERMAL RIDGE...SOUTH OF THE
BLACK HILLS INTO CENTRAL NORTH DAKOTA...HAS CONTRIBUTED TO
POTENTIALLY EXTREME INSTABILITY. THIS IS MOSTLY FOCUSED NORTH
NORTHEAST OF A SURFACE LOW CENTER...SOUTHWEST OF MOBRIDGE SD...
THROUGH THE BISMARCK ND AREA...WHERE LOW-LEVEL WARM ADVECTION
APPEARS MAXIMIZED NEAR SURFACE WARM FRONT. RUC GUIDANCE SUGGESTS
THAT MIXED LAYER CAPE HAS EXCEEDED 4000 J/KG...BUT CONSIDERABLE
INHIBITION REMAINS...AND TIMING OF CONVECTIVE INITIATION IS A BIT
UNCERTAIN.

HOWEVER...AN INCREASINGLY SHEARED MID-LEVEL IMPULSE...EMANATING FROM
THE NORTH CENTRAL ROCKIES EARLIER TODAY...IS IN THE PROCESS OF
LIFTING THROUGH THE WESTERN DAKOTAS. THIS COULD PROVIDE THE FORCING
FOR THE INITIATION OF CONVECTIVE DEVELOPMENT...POSSIBLY AS EARLY AS
THE 25/22-26/00Z TIME FRAME. IF THIS OCCURS...30+ KT SOUTHERLY 850
JET BENEATH 40-50 SOUTHWESTERLY 500 MB FLOW IS CONTRIBUTING TO
STRONG DEEP LAYER SHEAR SUFFICIENT FOR SUPERCELLS. ISOLATED
TORNADOES APPEAR POSSIBLE...BUT A WEAKNESS IN THE WIND FIELDS
BETWEEN 850 MB AND 500 MB...AND SIZABLE LOW-LEVEL TEMPERATURE DEW
POINT SPREADS SUGGEST THAT THE RISK FOR ISOLATED VERY LARGE HAIL AND
DAMAGING DOWNBURSTS WILL BE THE PRIMARY SEVERE THREATS INTO EARLY
EVENING.

OTHER STORMS APPEAR POSSIBLE LATE THIS AFTERNOON FARTHER TO THE
SOUTHWEST...NEAR THE BLACK HILLS...AND MAY INITIATE FIRST...AIDED BY
OROGRAPHIC FORCING IN POST-FRONTAL UPSLOPE REGIME ON THE NORTHERN
SLOPES OF THE BLACK HILLS.

.KERR.. 06/25/2007

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

ATTN...WFO...FGF...ABR...BIS...UNR...

47550164 48130031 47619886 45859960 44980078 44620247
43580376 43670488 44760445 45100376 45950239

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