SWODY1
SPC AC 130543
DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1243 AM CDT WED AUG 13 2008
VALID 131200Z - 141200Z
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE SERN STATES...
...THERE IS A SLGT RISK OF SVR TSTMS ACROSS THE CENTRAL/SRN HIGH
PLAINS NEWD TO SWRN MN...
...SYNOPSIS...
AN UPPER RIDGE IS EXPECTED TO BUILD NWD ACROSS THE PACIFIC NW AND
SWRN CANADA TODAY...WITH A TROUGH REMAINING LOCATED OVER THE ERN
STATES...ANCHORED TO A CLOSED LOW OVER QUEBEC. MEANWHILE...A CLOSED
LOW THAT WAS STATIONARY OVER SASKATCHEWAN ON TUESDAY IS FORECAST TO
MOVE SWD INTO ERN MT/WRN ND LATE IN THE DAY 1 FORECAST PERIOD. A
SHORT WAVE TROUGH...CURRENTLY LOCATED OVER THE NRN ROCKIES PER WATER
VAPOR IMAGERY...IS EXPECTED TO TRACK ESEWD REACHING THE NRN HIGH
PLAINS BY LATE AFTERNOON/EARLY EVENING. THIS TROUGH WILL BE
PRECEDED BY SEVERAL WEAKER MID LEVEL IMPULSES EMANATING FROM THE
GREAT BASIN AND TRACKING ESEWD WITHIN NWLY FLOW PATTERN EXTENDING
FROM THE NRN ROCKIES TO GULF COAST STATES. IN THE SOUTHEAST...A
SHORT WAVE TROUGH WILL TRACK ACROSS THE SERN STATES...REACHING ERN
SC/NC BY 14/00Z AND THEN TRACK NEWD TO OFF THE MID ATLANTIC COAST BY
12Z THURSDAY.
...SERN STATES...
IN THE LOW LEVELS...A SURFACE LOW SHOULD BE LOCATED ACROSS ERN AL AT
12Z TODAY...WITH A BOUNDARY EXTENDING EWD THROUGH SRN SC TO THE
COAST. THE LOW WILL TRACK EWD REACHING THE SC COAST BY LATE THIS
AFTERNOON...AND THEN MOVE NEWD ALONG OR JUST OFF THE NC COAST THIS
EVENING.
ONGOING SHOWERS WITH EMBEDDED TSTMS WILL BE LOCATED ACROSS MUCH OF
THE CENTRAL GULF COAST STATES EWD TO THE SERN STATES AT THE START OF
THE FORECAST PERIOD. ASSOCIATED CLOUDINESS IS EXPECTED TO INHIBIT
THE POTENTIAL FOR MUCH SURFACE HEATING TODAY...AND THIS COMBINED
WITH WEAK LAPSE RATES WILL PRECLUDE THE DEVELOPMENT OF STRONGER
INSTABILITY. IN ADDITION TO THE WEAK LAPSE RATES...ANOTHER LIMITING
FACTOR PRECLUDING HIGHER SEVERE WEATHER PROBABILITIES TODAY IS A
WEAKNESS OF HODOGRAPHS IN MID LEVELS RESULTING IN A LACK OF ROBUST
EFFECTIVE/DEEP-LAYER SHEAR.
ASCENT WILL SPREAD EWD AHEAD OF THE SERN U.S. SHORT WAVE TROUGH
WITHIN A VERY MOIST AND WEAKLY CAPPED AIR MASS. THIS WILL SUPPORT
SURFACE BASED INFLOW PARCELS FROM THE START OF THE FORECAST PERIOD
IN GA WITH ACTIVITY DEVELOPING AND SPREADING EWD TO THE SC/SRN NC
COAST PRIOR TO 14/00Z. ASIDE FROM THE FAVORED ENHANCED LOW LEVEL
SHEAR ZONE FROM THE SURFACE LOW EWD ALONG THE BOUNDARY WHERE LOW
LEVEL WINDS WILL BE BACKED...STRONG 50-60 KT SWLY LOW LEVEL WINDS
ACROSS SRN GA TO SRN SC WILL RESULT IN LARGE CURVED HODOGRAPHS.
THIS WILL PROMOTE AN INCREASED POTENTIAL FOR TORNADOES AND STRONG
WIND GUSTS BEFORE ACTIVITY MOVES OFFSHORE AROUND 14/00Z.
...CENTRAL/SRN HIGH PLAINS NEWD TO SWRN MN...
STRONGER WLY MID LEVEL WINDS...CURRENTLY TRANSLATING EWD ACROSS MT
WITHIN BASE OF SASKATCHEWAN CLOSED LOW...ARE EXPECTED TO REACH THE
MID MO VALLEY INTO SWRN MN BY MID-LATE AFTERNOON WITH STRONGER WINDS
DEVELOPING OVER THE CENTRAL HIGH PLAINS BY AFTERNOON. A PLUME OF
STEEP MID LEVEL LAPSE RATES /7-8 C/KM/ WILL SPREAD EWD ACROSS MUCH
OF SD TO KS AND ATOP A CORRIDOR OF LOWER 60S SURFACE DEWPOINTS
EXTENDING FROM THE CENTRAL HIGH PLAINS NEWD ALONG A TROUGH INTO SWRN
MN. A FEW TSTMS MAY BE ONGOING AT 12Z TODAY ACROSS NEB AND THE SRN
HIGH PLAINS...BUT SURFACE HEATING WITHIN THE FAVORABLE THERMODYNAMIC
ENVIRONMENT WILL LIKELY SUPPORT MODERATE INSTABILITY COINCIDENT WITH
THE MOISTURE CORRIDOR/SURFACE BOUNDARIES. FORECAST SOUNDINGS
INDICATE GENERALLY WEAK LOWER TROPOSPHERIC WINDS VEERING WITH HEIGHT
AND STRONGER MID-UPPER LEVEL WNWLY WINDS. THIS WILL RESULT IN DEEP
LAYER SHEAR OF 35-45 KT SUPPORTING MULTICELL STORMS AND SUPERCELLS
THIS AFTERNOON FROM THE CENTRAL HIGH PLAINS NEWD TO SWRN MN. HAIL
AND STRONG WIND GUSTS SHOULD BE THE PRIMARY THREATS.
ADDITIONAL TSTMS ARE EXPECTED TO DEVELOP BY LATE AFTERNOON/EARLY
EVENING OVER SERN WY/WRN NEB AS ASCENT ATTENDANT TO NRN ROCKIES
IMPULSE REACHES THIS REGION WHERE THE AIR MASS WILL BE MODERATELY
UNSTABLE. THIS ACTIVITY ALONG WITH OTHER STORMS LOCATED FARTHER S
THROUGH ERN CO AND NERN NM MAY GROW UPSCALE INTO SEVERAL ORGANIZED
CLUSTERS AND MOVE SSEWD ALONG THE HIGH PLAINS...AS A LLJ STRENGTHENS
AND EVENTUALLY VEERS TONIGHT.
..PETERS/CROSBIE.. 08/13/2008
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