MESO: Mesoscale Discussion 1859

ACUS11 KWNS 082152
SWOMCD
SPC MCD 082152
SDZ000-NDZ000-MTZ000-WYZ000-090015-

MESOSCALE DISCUSSION 1859
NWS STORM PREDICTION CENTER NORMAN OK
0452 PM CDT SUN SEP 08 2013

AREAS AFFECTED...PORTIONS OF SERN MT...CNTRL/SRN ND...WRN/CNTRL
SD...NERN/E-CNTRL WY

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 082152Z - 090015Z

PROBABILITY OF WATCH ISSUANCE...40 PERCENT

SUMMARY...AT LEAST ISOLATED SVR THUNDERSTORMS COULD OCCUR ACROSS
PARTS OF THE DAKOTAS AND ADJACENT MT/WY INTO THE EVENING HOURS...AND
CONVECTIVE TRENDS WILL BE MONITORED FOR POSSIBLE WW ISSUANCE.

DISCUSSION...WATER VAPOR IMAGERY SUGGESTS THAT LITTLE IN THE WAY OF
DEEP FORCING FOR ASCENT WILL BE PRESENT WITHIN A BROAD RIBBON OF
ENHANCED MID-LEVEL MOISTURE CRESTING A CNTRL-CONUS RIDGE. ALSO...SFC
OBSERVATIONS REVEAL LIMITED CONVERGENCE AMIDST A WEAK-FLOW PATTERN
WITHIN A RELATIVELY MOIST -- ALBEIT NOT PARTICULARLY WARM -- AIR
MASS LOCATED N OF A WAVY...QUASI-STATIONARY FRONT ANALYZED FROM SRN
SD INTO THE NEB PANHANDLE AND ERN WY. THIS IS WHERE THE
JUXTAPOSITION OF SFC DEWPOINTS IN THE LOWER/MIDDLE 60S WITH
TEMPERATURES IN THE MIDDLE 70S TO THE LOWER 80S BENEATH MODESTLY
STEEP MID-LEVEL LAPSE RATES IS SUPPORTING MODERATE INSTABILITY.
ABUNDANT AREAS OF MULTI-LAYERED CLOUDS HAVE LIMITED DIABATIC SFC
HEATING/DESTABILIZATION...AND THERE IS SUBSTANTIAL UNCERTAINTY
REGARDING THE COVERAGE OF ROBUST CONVECTIVE DEVELOPMENT AND
ASSOCIATED SVR POTENTIAL.

REGARDLESS...SUFFICIENT LOW-LEVEL ASCENT COULD EXIST INVOF
ILL-DEFINED BOUNDARIES/WIND-SHIFT AXES/TERRAIN-DRIVEN
CIRCULATIONS -- E.G. A WIND-SHIFT AXIS LYING FROM WRN ND TO
NERN WY -- FOR AT LEAST ISOLATED DEEP CONVECTION TO CONTINUE INTO
THE EVENING HOURS. ALSO...SOME UPTICK IN CONVECTION MAY OCCUR IN
ASSOCIATION WITH INCREASING ASCENT WITHIN THE EXIT-REGION OF A
NOCTURNALLY STRENGTHENING LOW-LEVEL JET STREAM OVER THE LOWER PLAINS
LATER THIS EVENING. GIVEN THE PRESENCE OF 30-50 KT OF MID-LEVEL FLOW
PER AREA VWP DATA...DEEP SHEAR MAY BE SUFFICIENT FOR A FEW
SUSTAINED/ORGANIZED CONVECTIVE STRUCTURES...WHICH COULD ALSO SPREAD
E OF ONGOING WW 516. A CONDITIONAL POTENTIAL FOR SVR WIND/HAIL MAY
OCCUR WITH SUCH ACTIVITY...THOUGH INCREASING NOCTURNAL
BOUNDARY-LAYER CINH MAY REDUCE ANY SVR WIND THREAT WITH TIME INTO
THE EVENING HOURS.

..COHEN/EDWARDS.. 09/08/2013

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

ATTN...WFO...FGF...ABR...BIS...UNR...CYS...BYZ...GGW...RIW...

LAT...LON 43820070 42850475 42830599 43450649 44740614 46630567
47310340 48180119 47759940 45669858 43820070

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