DAY1SVR: Day 1 Convective Outlook

ACUS01 KWNS 081950
SWODY1
SPC AC 081948

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0248 PM CDT SUN SEP 08 2013

VALID 082000Z - 091200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM PARTS OF MT/WY EWD INTO
PORTIONS OF THE DAKOTAS...

PREVIOUS FORECAST REASONING ACROSS THE SLGT RISK AREA APPEARS TO BE
ON TRACK...ONLY MINOR CHANGES HAVE BEEN MADE TO THE SEVERE WEATHER
PROBABILITIES. FOR SHORT-TERM DETAILS REGARDING THE EVOLVING SEVERE
WEATHER THREAT OVER PARTS OF MT/WY...REFER TO MCD 1857 AND WW 516.
OTHERWISE...STORMS ARE FORECAST TO INCREASE IN COVERAGE LATE THIS
AFTERNOON INTO THE NIGHT OVER NERN WY AND SD AS SURFACE LOW PRESSURE
DEEPENS AND THE EXIT REGION OF A 40+ KT LLJ SETS UP OVER THE AREA.
SUPERCELLS AND LARGE HAIL WILL BE POSSIBLE INITIALLY...WITH STORM
MERGERS GIVING WAY TO UPSCALE GROWTH INTO AN MCS...WHICH MAY YIELD A
CORRIDOR OF ENHANCED DAMAGING WIND POTENTIAL.

FARTHER SE...CLUSTERS OF STORMS WILL BE POSSIBLE THROUGH THIS
EVENING FROM STJ IN NWRN MO/NERN KS INTO THE MID-SOUTH REGION /AHEAD
OF AN MCV LOCATED SE OF STL/. BEST POTENTIAL FOR STRONG/SEVERE WIND
GUSTS WILL BE WHERE HOT TEMPERATURES/STEEP LOW-LEVEL LAPSE RATES ARE
COLLOCATED WITH A HIGH PW AIRMASS. MARGINAL SEVERE THREAT SHOULD
DIMINISH THIS EVENING.

..GARNER.. 09/08/2013

.PREV DISCUSSION... /ISSUED 1108 AM CDT SUN SEP 08 2013/

...SYNOPSIS...

AN UPPER HIGH CENTERED OVER THE CNTRL PLAINS WILL SHIFT EWD INTO THE
OZARKS IN RESPONSE TO THE EWD PROGRESSION OF AN UPPER LOW FROM THE
NRN INTERMOUNTAIN REGION INTO THE NRN HIGH PLAINS. THIS PATTERN
EVOLUTION WILL RESULT IN STRENGTHENING LARGE-SCALE FORCING FOR
ASCENT AND MID AND UPPER-LEVEL FLOW FROM THE NRN HIGH PLAINS TOWARD
UPPER MS VALLEY.

IN THE LOW LEVELS...A LEE CYCLONE OVER NWRN NEB WILL DEEPEN WHILE
DEVELOPING INTO NERN SD BY 9/12Z. AN ASSOCIATED SURFACE FRONT
CURRENTLY EXTENDING FROM THE LOW ESEWD THROUGH ERN NEB...SRN IA INTO
THE OH VALLEY WILL LIFT NWD IN RESPONSE TO A STRENGTHENING LOW-LEVEL
WAA REGIME DOWNSTREAM FROM THE MIGRATORY CYCLONE. MEANWHILE...A
DEVELOPING PACIFIC FRONT FROM THE NRN ROCKIES INTO GREAT BASIN WILL
ADVANCE EWD THROUGH WRN PARTS OF THE DAKOTAS AND NEB BY THE END OF
THE FORECAST PERIOD.

...PARTS OF MT/WY INTO THE DAKOTAS THIS AFTERNOON INTO TONIGHT...

12Z SOUNDINGS AND SATELLITE-DERIVED PW IMAGERY SHOW THE CONTINUED
PRESENCE OF A SEASONABLY MOIST AIR MASS INVOF OF STALLED SYNOPTIC
FRONT WITH BOUNDARY LAYER DEWPOINTS IN THE 60S TO LOWER 70S AND PW
VALUES OF 1.2-1.8 INCHES. DECREASING MORNING CLOUDINESS COUPLED
WITH THIS HIGH MOISTURE CONTENT AND STEEP MIDLEVEL LAPSE RATES WILL
YIELD A MODERATELY UNSTABLE ENVIRONMENT BY AFTERNOON WITH MLCAPE
VALUES RANGING FROM 1000-1500 J/KG OVER MT TO AS HIGH AS 2000-3000
J/KG ACROSS SD.

CONVECTIVE EVOLUTION WILL BE DICTATED TO SOME DEGREE BY THE AREAL
COVERAGE AND EXTENT OF LINGERING CLOUDS. BUT IN GENERAL...IT
APPEARS THAT HEATING ALONG THE ELEVATED TERRAIN OF MT...WY...AND WRN
SD...ALONG WITH INCREASING CONVERGENCE INVOF THE SYNOPTIC LOW AND
NWD-DEVELOPING WARM FRONT WILL BE THE PRIMARY FOCI FOR STRONG TO
SEVERE TSTM DEVELOPMENT THIS AFTERNOON INTO EVENING.

GIVEN THE PRESENCE OF A VERTICALLY VEERING WIND PROFILE AND
STRENGTHENING MID TO UPPER-LEVEL FLOW --AND RESULTANT VERTICAL
SHEAR-- INITIAL STORM MODE WILL LIKELY BE SUPERCELLULAR WITH A RISK
FOR LARGE HAIL...DAMAGING WINDS...AND PERHAPS A BRIEF TORNADO.
AGGREGATING STORM-SCALE COLD POOLS AND THE DEVELOPMENT OF A
NOCTURNAL LOW-LEVEL WIND MAXIMUM --WHICH WILL BE STRONGER AND
BROADER THAN PAST NIGHTS-- WILL SUPPORT UPSCALE GROWTH OF STORMS
INTO ONE OR MORE MCSS WITH THE RISK FOR DAMAGING WINDS AND HAIL
CONTINUING INTO TONIGHT...MAINLY ACROSS NRN SD/SRN ND.

...OZARKS THIS AFTERNOON INTO EARLY EVENING...

WEAK LOW-LEVEL WAA IS EXPECTED TO PERSIST TODAY...ENHANCING
INFLOW/ASCENT ALONG THE WRN FLANK OF NOCTURNAL MCS ONGOING ACROSS
PARTS OF CNTRL MO. THIS SHOULD SUPPORT REGENERATIVE STORM
DEVELOPMENT ON THE WRN END OF THE RESIDUAL MCS WHERE DAYTIME HEATING
AND BOUNDARY LAYER DEWPOINTS OF 65-70 F WILL PROMOTE MLCAPE
APPROACHING 1500-2500+ J/KG. VERTICAL SHEAR WILL REMAIN RATHER
WEAK...LIMITING THE POTENTIAL FOR STORM ORGANIZATION.
NONETHELESS...LOCALLY DAMAGING WIND GUSTS WILL BE POSSIBLE OWING TO
THE DEGREE OF INSTABILITY AND HIGH PW ENVIRONMENT.

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