SWODY1
SPC AC 311240
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0740 AM CDT WED AUG 31 2011
VALID 311300Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN MT ACROSS ND INTO NWRN
MN...
...ERN MT ACROSS ND INTO NWRN MN...
LARGER SCALE POSITIVELY TILTED UPPER TROUGH OVER THE PACIFIC NW IS
FORECAST TO MOVE SLOWLY EWD TOWARD THE NRN INTERMOUNTAIN REGION...AS
A SHORT WAVE TROUGH MOVING NEWD INTO WRN WY MOVES TOWARD THE DAKOTAS
WITHIN A BAND OF STRONGER SWLY FLOW ALOFT IN ADVANCE OF THE PACIFIC
NW SYSTEM. AT THE SURFACE...A LOW OVER SOUTH CENTRAL MT IS EXPECTED
TO SHIFT INTO ERN MT AND DEEPEN TODAY BEFORE MOVING NEWD ACROSS
WRN/NRN ND REACHING SRN MANITOBA BY THE END OF THE PERIOD. A NE/SW
ORIENTED COLD FRONT EXTENDING FROM SERN SASKATCHEWAN SWWD THROUGH
THE LOW AND INTO SWRN MT WILL BEGIN TO MOVE EWD LATER TODAY AND
TONIGHT INTO THE NRN PLAINS.
STRENGTHENING SOUTHERLY LOW LEVEL WINDS OVER THE PLAINS WILL
TRANSPORT INCREASING MOISTURE NWD TODAY. DEW POINTS IN THE
MID/UPPER 60S ARE EXPECTED TO SPREAD INTO PARTS OF THE CENTRAL/ERN
DAKOTAS THIS AFTERNOON...WITH MOISTURE DECREASING WWD INTO THE 50S
OVER ERN MT. THE SWLY FLOW ALOFT WILL ALLOW A PLUME OF STEEP MID
LEVEL LAPSE RATES/EML TO OVERSPREAD THE DAKOTAS TODAY...RESULTING IN
INCREASING POTENTIAL INSTABILITY /MLCAPE 2000-2500 J PER KG OVER THE
CENTRAL AND ERN DAKOTAS/ AS STRONG DIABATIC HEATING OCCURS THIS
AFTERNOON. HOWEVER...THE PRESENCE OF THE EML IS ALSO EXPECTED TO
INHIBIT DEVELOPMENT OF SURFACE-BASED DEEP CONVECTION WITHIN THE WARM
SECTOR THIS AFTERNOON.
THUNDERSTORMS ARE EXPECTED TO INCREASE OVER PARTS OF ERN MT BY THIS
AFTERNOON AS LARGE SCALE ASCENT IN ADVANCE OF THE WY SHORT WAVE
TROUGH COUPLES WITH LOW LEVEL CONVERGENCE ALONG THE COLD FRONT.
STORMS ARE EXPECTED TO EVENTUALLY GROW UPSCALE INTO AN MCS AND
SPREAD EWD/NEWD THROUGH TONIGHT AS THEY ENCOUNTER INCREASING
MOISTURE WITH EWD EXTENT ACROSS PARTS OF ND...WITH ACTIVITY REACHING
NWRN MN LATE TONIGHT. MAINTENANCE OF A NOCTURNAL MCS WILL BE AIDED
BY STRONG LOW LEVEL CONVERGENCE/WARM ADVECTION ASSOCIATED WITH AN
INTENSIFYING LOW LEVEL JET OVER THE NRN PLAINS. WIND PROFILES ARE
FORECAST TO VEER AND INCREASE IN SPEED WITH HEIGHT...PROVIDING
SUFFICIENT DEEP LAYER SHEAR TO ENHANCE STORM ORGANIZATION AND
INTENSITY. A FEW SEVERE STORMS ARE LIKELY WITH DAMAGING WIND GUSTS
AND LARGE HAIL BEING THE PRIMARY THREATS.
...SD...
FARTHER SOUTH OVER SD THERE IS MORE UNCERTAINTY CONCERNING
CONVECTIVE INITIATION AS THE EML/CAPPING INVERSION IS EXPECTED TO
INHIBIT SURFACE-BASED THUNDERSTORMS DURING THE AFTERNOON. ALTHOUGH
MODEL GUIDANCE IS QUITE CONSISTENT INDICATING STORMS WILL MOVE FROM
ERN MT ACROSS ND TOWARD NWRN MN DURING THE PERIOD...THERE IS
CONSIDERABLE VARIABILITY IN MESOSCALE AND CONVECTION-ALLOWING MODEL
SOLUTIONS FOR CONVECTIVE DEVELOPMENT OVER SD. ISOLATED STORMS WILL
BE POSSIBLE...ESPECIALLY DURING THE LATE AFTERNOON AND EVENING WHEN
STRONG LOW LEVEL HEATING WILL WEAKEN THE CAP WITHIN THE LOW LEVEL
MOISTURE/INSTABILITY AXIS. THE FAVORABLE CAPE/SHEAR ENVIRONMENT
WILL SUPPORT A RISK FOR LARGE HAIL AND DAMAGING WIND GUSTS FOR ANY
SUSTAINED UPDRAFTS THAT CAN OCCUR. HOWEVER...MINIMAL FORCING FOR
LARGE SCALE ASCENT IS EXPECTED TO LIMIT OVERALL STORM COVERAGE...SO
WILL MAINTAIN A LOW PROBABILITY FOR SEVERE STORMS AT THIS TIME.
..WEISS/SMITH.. 08/31/2011
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