SWODY2
SPC AC 300540
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1240 AM CDT MON AUG 30 2010
VALID 311200Z - 011200Z
...THERE IS A SLGT RISK OF SVR TSTMS TUE AFTN AND EVE ACROSS PARTS
OF THE CNTRL PLAINS INTO THE UPPER MS VALLEY/GREAT LAKES REGION...
...SYNOPSIS...
COINCIDENT WITH THE NORTHEASTWARD ACCELERATION OF A SIGNIFICANT
EMBEDDED SHORT WAVE TROUGH OUT OF THE GREAT BASIN...IT STILL APPEARS
LIKELY THAT THE BROADER SCALE WESTERN U.S. TROUGH...AND DOWNSTREAM
RIDGE...WILL BECOME LESS AMPLIFIED TODAY INTO TUESDAY. THE BELT OF
STRONGER WESTERLIES IS EXPECTED TO BECOME MORE ZONAL ACROSS SOUTHERN
CANADA AND THE NORTHERN TIER OF THE U.S...AND MODELS SUGGEST THAT
THE EMBEDDED IMPULSE WILL GRADUALLY TURN EASTWARD ACROSS ONTARIO
LATE TUESDAY/TUESDAY NIGHT...AFTER LIFTING NORTH OF THE CENTRAL
CANADIAN/U.S. BORDER AREA. JUST HOW FAST THIS OCCURS...AND
LINGERING MID-LEVEL RIDGING CENTERED NEAR THE APPALACHIANS
WEAKENS...REMAINS A POINT OF CONSIDERABLE MODEL VARIABILITY. BUT
ANOTHER SIGNIFICANT SHORT WAVE IMPULSE IS PROGGED TO DIG EAST
SOUTHEASTWARD ACROSS THE CANADIAN AND NORTHERN U.S.
ROCKIES...QUICKLY ON THE HEELS OF THE ONTARIO SYSTEM.
THE SURFACE CYCLONE ASSOCIATED WITH THE LEAD SYSTEM IS STILL PROGGED
TO MIGRATE WELL NORTH OF THE UPPER GREAT LAKES REGION BY EARLY
TUESDAY. AS THIS OCCURS...SUBSTANTIAL WEAKENING OF A SOUTHERLY
LOW-LEVEL JET APPEARS LIKELY ACROSS THE CENTRAL PLAINS INTO THE
UPPER MISSISSIPPI VALLEY/GREAT LAKES...WITH AN ASSOCIATED
PRE-FRONTAL WIND SHIFT/CONFLUENCE ZONE TENDING TO SHIFT SOUTH OF THE
STRONGER MID-LEVEL FLOW. HOWEVER...A NARROW PLUME OF HIGH MOISTURE
CONTENT AIR ALONG AND SOUTHEAST OF THIS FEATURE IS EXPECTED TO
CONTRIBUTE TO SUFFICIENT DESTABILIZATION FOR SCATTERED THUNDERSTORM
ACTIVITY THROUGH THE PERIOD...AS FAR SOUTH AND WEST AS THE SOUTHERN
ROCKIES AND ADJACENT PLATEAU REGION.
ANOTHER AREA WITH HIGHER THUNDERSTORM PROBABILITIES DURING THIS
PERIOD MAY EXIST WITH A WESTWARD MOVING WAVE ACROSS THE WESTERN AND
CENTRAL GULF COAST/LOWER MISSISSIPPI VALLEY REGION...IN THE PRESENCE
OF HIGH MOISTURE CONTENT AND FAVORABLE INSTABILITY. OTHERWISE...AT
LEAST LOW THUNDERSTORM PROBABILITIES MAY ACCOMPANY A REMNANT
CYCLONIC SHEAR AXIS TO THE WEST OF THE UPPER RIDGE... ACROSS THE
LOWER OHIO VALLEY INTO PARTS OF THE LOWER GREAT LAKES REGION...AND
NEAR THE STRONGER WESTERLIES...ACROSS PARTS OF MONTANA AND NORTHERN
NEW ENGLAND.
...CENTRAL PLAINS INTO THE UPPER MS VALLEY/GREAT LAKES REGION...
MODELS INDICATE THAT STRONG SURFACE HEATING BENEATH AN INITIALLY
CAPPING RESIDUAL ELEVATED MIXED LAYER...COUPLED WITH SURFACE DEW
POINTS AROUND 70F...WILL CONTRIBUTE TO MODERATELY STRONG BOUNDARY
LAYER DESTABILIZATION TUESDAY...FROM PARTS OF THE CENTRAL PLAINS
INTO THE UPPER MISSISSIPPI VALLEY. BY PEAK HEATING...MIXED LAYER
CAPE OF AT LEAST 2000-3000 J/KG APPEARS PROBABLE...PARTICULARLY
ALONG AN AXIS FROM SOUTHERN/EASTERN NEBRASKA INTO SOUTHEASTERN
MINNESOTA...WHERE MID-LEVEL COOLING IS EXPECTED TO WEAKEN INHIBITION
DURING THE MID TO LATE AFTERNOON HOURS.
ALTHOUGH WEST SOUTHWESTERLY LOWER/MID TROPOSPHERIC FLOW MAY BE
SOMEWHAT MODEST...AROUND 30 KTS...IT SHOULD BE SUFFICIENT...IN
CONJUNCTION WITH HEAVY PRECIPITATION LOADING AND EVAPORATIVE COOLING
ASSOCIATED WITH AT LEAST MODESTLY LARGE BOUNDARY LAYER
TEMPERATURE-DEW POINT SPREADS...TO SUPPORT THE RISK FOR POTENTIALLY
DAMAGING DOWNBURSTS...AND STRONG SURFACE COLD POOL DEVELOPMENT.
WITH A SQUALL LINE EXPECTED TO EVOLVE...THIS THREAT MAY PERSIST AND
SPREAD EAST SOUTHEASTWARD WELL INTO THE EVENING HOURS BEFORE
CONVECTION WEAKENS WITH BOUNDARY LAYER STABILIZATION.
ALTHOUGH INSTABILITY IS EXPECTED TO BE WEAKER...LINGERING STRONGER
FLOW FIELDS MAY SUPPORT SEVERE POTENTIAL AS FAR NORTHEAST AS THE
UPPER GREAT LAKES REGION.
..KERR.. 08/30/2010
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