SWODY1
SPC AC 311624
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1124 AM CDT WED AUG 31 2011
VALID 311630Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON AND TONIGHT FROM
PARTS OF ERN MT ACROSS NRN ND...
...NRN HIGH PLAINS EWD/SEWD THROUGH THE DAKOTAS AND NEB...
WELL-DEFINED VORTICITY MAXIMUM AND ASSOCIATED 50-60 KT MIDLEVEL JET
STREAK OVER THE COLUMBIA PLATEAU INTO NRN INTER-MOUNTAIN REGION WILL
EJECT NEWD THROUGH THE NRN HIGH PLAINS INTO SK/MB BY TONIGHT. THIS
SYSTEM WILL BE PRECEDED BY A WEAKENING MIDLEVEL IMPULSE PROGRESSING
ENEWD FROM WY INTO THE DAKOTAS. IN THE LOW LEVELS...SURFACE LOW
OVER ERN MT WILL DEVELOP NEWD ALONG ATTENDANT QUASI-STATIONARY
BOUNDARY INTO SRN MB WHILE TRAILING EXTENSION OF BAROCLINIC ZONE
ADVANCES THROUGH THE NRN HIGH PLAINS AS A COLD FRONT. ELSEWHERE...A
LEE TROUGH WILL STRENGTHEN TODAY...EXTENDING FROM THE ERN MT SURFACE
LOW SWD THROUGH WRN NEB.
AN EML AND ASSOCIATED CAP WILL BE ADVECTED NEWD ACROSS THE NRN/CNTRL
PLAINS INTO UPPER MS VALLEY AS MIDLEVEL HEIGHT FIELD TIGHTENS IN
ADVANCE OF NRN ROCKIES IMPULSE. AT THE SAME TIME...A MOIST BOUNDARY
LAYER /I.E. DEWPOINTS IN THE MID TO UPPER 60S/ CURRENTLY OBSERVED
FROM ERN SD INTO THE MID-MO VALLEY WILL BE ADVECTED NWWD. THESE
DIFFERENTIAL ADVECTIONS WILL YIELD A MODERATELY UNSTABLE /BUT
CAPPED/ AIR MASS BY AFTERNOON FROM THE VICINITY OF THE SURFACE LOW
OVER ERN MT SWD ALONG LEE TROUGH WHERE MLCAPE WILL APPROACH
1500-2500 J/KG. FARTHER W ALONG FRONT OVER CNTRL MT...A DRIER
BOUNDARY LAYER WILL LIMIT AFTERNOON MLCAPE TO 500-1000 J/KG.
THE HIGHEST PROBABILITY OF SURFACE-BASED TSTM DEVELOPMENT APPEARS TO
BE ALONG OR PERHAPS ON THE IMMEDIATE COOL SIDE OF SURFACE FRONT OVER
MT LATER TODAY AHEAD OF EJECTING MIDLEVEL SYSTEM. HERE...
STRENGTHENING MIDLEVEL WIND FIELD WILL ALIGN WITH A STEEP-LAPSE RATE
ENVIRONMENT...SUPPORTING A THREAT FOR HIGH-BASED SUPERCELLS AND/OR
BOWING STRUCTURES CAPABLE OF DAMAGING WINDS AND HAIL. UPSCALE
GROWTH INTO AN MCS IS ANTICIPATED TONIGHT AS MOIST INFLOW IS
ENHANCED BY A 50+ KT NOCTURNAL LLJ. THIS MAY RESULT IN A CONTINUED
THREAT FOR DAMAGING WINDS AND HAIL...PRIMARILY ACROSS THE NRN HALF
OF ND.
FARTHER SE...STRONG DAYTIME HEATING AND POTENTIAL INFLUENCE OF
WEAKENING WY SHORT-WAVE TROUGH MAY CONTRIBUTE TO ISOLATED STORM
DEVELOPMENT ALONG THE LEE TROUGH THIS AFTERNOON/EVENING FROM CNTRL
SD INTO WRN NEB. HERE...THE COMBINATION OF MODERATE INSTABILITY AND
30-35 KT OF DEEP WLY SHEAR WILL SUPPORT SUPERCELLS CAPABLE OF HAIL
AND DAMAGING WINDS. HOWEVER...GIVEN THE STRONG CAP AND UNCERTAINTY
IN CONVECTIVE STORM COVERAGE...ONLY LOW SEVERE PROBABILITIES WILL BE
INCLUDED.
..MEAD/GRAMS.. 08/31/2011
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