Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 231620
SWODY1
SPC AC 231618

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1118 AM CDT SAT AUG 23 2014

VALID 231630Z - 241200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE NRN PLAINS
INTO UPPER MS VALLEY...

...SUMMARY...
WIDELY SCATTERED SEVERE THUNDERSTORMS ARE EXPECTED TO DEVELOP ACROSS
PARTS OF THE NORTHERN PLAINS INTO WESTERN MINNESOTA TODAY INTO
TONIGHT.  LARGE HAIL...DAMAGING WINDS...AND A FEW TORNADOES MAY
OCCUR.

...SYNOPSIS...

AN UPPER LOW OVER THE NRN INTERMOUNTAIN REGION WILL UNDERGO FURTHER
DEEPENING WHILE DEVELOPING EWD INTO THE NRN HIGH PLAINS...DUE IN
PART TO THE PROGRESSION OF A VORTICITY MAXIMUM AND ASSOCIATED
MID-LEVEL JET STREAK PROGRESSING FROM THE GREAT BASIN INTO THE NRN
PLAINS. THIS VORTICITY MAXIMUM WILL BE PRECEDED BY A PERTURBATION
WHICH WILL WEAKEN WHILE TRACKING FROM THE CNTRL HIGH PLAINS THROUGH
THE MID MO VALLEY.

AT THE SURFACE...MID-MORNING MESOANALYSIS REVEALED A COUPLE OF
SURFACE LOWS...ONE OVER SWRN SD AND THE OTHER OVER FAR SWRN NEB.
THESE TWO FEATURES WILL GRADUALLY CONSOLIDATE INTO A DEEPENING
CYCLONE WHICH WILL DEVELOP NWD THROUGH CNTRL SD INTO CNTRL
ND...ALONG THE ERN EDGE OF A WEDGE OF COOLER AIR SETTLING SWD
THROUGH THE NRN HIGH PLAINS. AN ASSOCIATED WARM FRONT WILL PIVOT WWD
THROUGH THE ND-MN RED RIVER VALLEY WHILE A MORE
PROMINENT...SECONDARY WARM FRONT DEVELOPS NWD THROUGH THE MID MO
VALLEY. MEANWHILE...A COLD FRONT ASSOCIATED WITH THE GREAT BASIN
SHORT-WAVE TROUGH WILL EMERGE FROM THE HIGH TERRAIN OF WY/CO BEFORE
SURGING EWD ACROSS WRN PARTS OF SD/NEB.

...NRN PLAINS/UPPER MS VALLEY THIS AFTERNOON/EVENING...

CONSIDERABLE EARLY-DAY CLOUDS ARE PRESENT ACROSS THE REGION WHICH
WHEN COUPLED WITH WEAK LAPSE RATES ALOFT MAY SLOW THE
DESTABILIZATION PROCESS. HOWEVER...LATEST MODEL GUIDANCE SUGGESTS
THAT STRONG BOUNDARY-LAYER HEATING WILL OCCUR IN THE WAKE OF THE
OVERNIGHT MCS ACROSS PORTIONS OF ERN NEB AND IA...ALONG AND TO THE
SOUTH OF THE NWD-MOVING WARM FRONT. THIS HEATING IN CONJUNCTION WITH
DEWPOINTS IN THE UPPER 60S TO LOWER 70S WILL FOSTER A CORRIDOR OF
MODERATE INSTABILITY BY AFTERNOON WITH MLCAPE OF 1500-2500+ J/KG.

CURRENT THINKING IS THAT SURFACE-BASED STORM DEVELOPMENT WILL BECOME
INCREASINGLY LIKELY BY LATE AFTERNOON OR EARLY EVENING INVOF THE
DEEPENING SURFACE LOW OVER S-CNTRL SD EWD/SEWD ALONG THE WARM FRONT
INTO SERN SD/FAR NERN NEB. THOUGH THE DEEP-LAYER FLOW FIELD WILL BE
LARGELY MERIDIONAL...BACKED NEAR-SURFACE WINDS ALONG THE WARM FRONT
WILL YIELD SIZABLE...CLOCKWISE-CURVED HODOGRAPHS IN THE LOW LEVELS.
AND WHILE A MIXTURE OF STORM MODES IS EXPECTED...THE ENHANCED
STREAMWISE VORTICITY AND MOIST...LOW LCL BOUNDARY LAYER WILL BE
SUPPORTIVE OF LOW-LEVEL MESOCYCLOGENESIS AND A RISK FOR A FEW
TORNADOES. OTHERWISE...EXPECT THAT DAMAGING WINDS AND SOME HAIL WILL
BE THE PRIMARY HAZARDS AS STORMS CONTINUE NEWD INTO PARTS OF WRN MN
THIS EVENING INTO TONIGHT.

...OH VALLEY/MIDWEST THIS AFTERNOON/EVENING...

THE 12Z DVN/ILX SOUNDINGS SAMPLED THE PRESENCE OF A VERY MOIST AIR
MASS /LOWEST 100-MB MEAN MIXING-RATIOS OF 18-19 G PER KG/ WHICH WHEN
COUPLED WITH DAYTIME HEATING WILL CONTRIBUTE TO A STRONGLY UNSTABLE
ENVIRONMENT BY AFTERNOON WITH MLCAPE OF 3000-4000+ J/KG. LARGE-SCALE
FORCING FOR ASCENT WILL REMAIN GENERALLY WEAK OWING TO THE PROXIMITY
OF THE UPPER RIDGE. HOWEVER...AN ACTIVE COLD POOL ATTENDANT TO THE
REMNANTS OF A NOCTURNAL MCS CURRENTLY ONGOING OVER FAR ERN IA INTO
SWRN WI AND NRN IL IS EXPECTED TO FOCUS THE REDEVELOPMENT OF
VIGOROUS STORMS THIS AFTERNOON.

BOTH VERTICAL SHEAR AND MID-LEVEL LAPSE RATE WILL REMAIN
WEAK...LIMITING THE POTENTIAL FOR ORGANIZED STORM MODES.
NONETHELESS...THE DEGREE OF INSTABILITY AND HIGH PW AIR MASS SUGGEST
THE POTENTIAL FOR EXCESSIVE WATER LOADING IN CONVECTIVE DOWNDRAFTS
AND A RISK FOR DAMAGING SURFACE WINDS.

FOR ADDITIONAL NEAR-TERM GUIDANCE...SEE MCD 1602.

...PORTIONS OF THE NRN/CNTRL HIGH PLAINS THIS AFTERNOON/EVENING...

INCREASING HEIGHT FALLS AND VERTICAL SHEAR ASSOCIATED WITH THE GREAT
BASIN VORTICITY MAXIMUM WILL INTERACT WITH A MODESTLY UNSTABLE
/MLCAPE OF 500-1000 J PER KG/ ENVIRONMENT TO FOSTER A BAND OF TSTMS
ALONG THE COLD FRONT OVER PARTS OF THE NEB PNHDL AND NERN CO
/PERHAPS INTO SWRN SD/ LATER THIS AFTERNOON. SOME HAIL AND/OR
LOCALLY DAMAGING WINDS MAY ACCOMPANY THE STRONGEST STORMS INTO THE
EVENING HOURS.

..MEAD/MARSH.. 08/23/2014



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