SWODY2
SPC AC 310541
DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1241 AM CDT TUE AUG 31 2010
VALID 011200Z - 021200Z
...THERE IS A SLGT RISK OF SVR TSTMS WED AND WED NIGHT ACROSS PARTS
OF THE CNTRL/NRN PLAINS AND MID MO VALLEY...
...SYNOPSIS...
THE UPPER FLOW PATTERN APPEARS TO BE TRENDING TOWARD A MORE ZONAL
REGIME...WITH THE STRONGER WESTERLIES GENERALLY BECOMING CONFINED TO
SOUTHERN CANADA AND THE NORTHERN TIER OF THE U.S...MUCH AS HAS BEEN
SUGGESTED BY MODEL GUIDANCE THE PAST FEW DAYS. CONSIDERABLE SPREAD
PERSISTS CONCERNING SMALLER SCALE DEVELOPMENTS...BUT RIDGING
CENTERED ACROSS THE MID ATLANTIC STATES IS EXPECTED TO WEAKEN
THROUGH WEDNESDAY...IN RESPONSE TO THE PROGRESSION OF A COUPLE OF
SIGNIFICANT EMBEDDED SHORT WAVE IMPULSES...AS HURRICANE EARL
MIGRATES NORTHWESTWARD TO THE EAST OF THE BAHAMAS.
ONE OF THESE IMPULSES APPEARS LIKELY TO GRADUALLY TURN EAST OF
HUDSON BAY WEDNESDAY AND WEDNESDAY NIGHT...WHILE ANOTHER DIGS TO THE
LEE OF THE NORTHERN ROCKIES...BEFORE TURNING EASTWARD TOWARD THE
UPPER MISSISSIPPI VALLEY. A COLD FRONT ASSOCIATED WITH THE LEAD
FEATURE IS EXPECTED TO ADVANCE SOUTHWARD INTO THE GREAT LAKES/MIDDLE
MISSISSIPPI VALLEY AND CENTRAL PLAINS BY 12Z WEDNESDAY...BEFORE
STALLING AND WEAKENING...PARTICULARLY OVER THE PLAINS. LATEST MODEL
RUNS APPEAR FAIRLY SIMILAR...SUGGESTING THAT THE TRAILING FEATURE
MAY BE ACCOMPANIED SURFACE CYCLOGENESIS ACROSS SOUTHERN SOUTH DAKOTA
INTO SOUTHERN MINNESOTA DURING THE LATTER HALF OF THE PERIOD.
...PLAINS/UPPER MS VALLEY INTO THE GREAT LAKES REGION...
A NARROWING PLUME OF HIGH MOISTURE CONTENT AIR /WITH PRECIPITABLE
WATER AROUND 2 INCHES/ ALONG AND TO THE SOUTHEAST OF THE LEAD
FRONTAL ZONE MAY BE SUPPORTING CONSIDERABLE CONVECTIVE DEVELOPMENT
FROM PORTIONS OF THE SOUTH CENTRAL PLAINS NORTHEASTWARD INTO THE
GREAT LAKES AT THE START OF THE PERIOD. WITH LITTLE FURTHER
SOUTHWARD PROGRESSION OF THE FRONT...LINGERING CLOUD COVER MAY LIMIT
DESTABILIZATION THROUGH THE DAY. AND THIS...COUPLED WITH FURTHER
WEAKENING OF DEEP LAYER SOUTHWESTERLY MEAN FLOW...PROBABLY WILL
MINIMIZE THE RISK FOR SEVERE STORMS ALONG THE REMNANT FRONT THROUGH
THE PERIOD.
MODELS DO INDICATE THAT MID-LEVEL LAPSE RATES WILL REMAIN FAIRLY
STEEP ACROSS MUCH OF THE CENTRAL AND NORTHERN PLAINS...WITH ELEVATED
MIXED LAYER AIR ADVECTING BACK NORTHEASTWARD THROUGH THE REGION
DURING THE DAY...AHEAD OF THE APPROACHING SHORT WAVE TROUGH. AS
LOW-LEVEL MOISTURE RETURNS NORTHWARD...THE DEVELOPMENT OF MODERATELY
LARGE CAPE /ON THE ORDER OF 2000+ J PER KG/ STILL APPEARS PROBABLE
FROM NORTHERN KANSAS INTO THE DAKOTAS.
THE DEGREE OF STRENGTHENING OF SOUTHERLY LOW-LEVEL FLOW REMAINS
UNCLEAR...BUT MID LEVEL FLOW FIELDS ACROSS THE REGION ARE EXPECTED
TO REMAIN AT LEAST MODERATELY STRONG THROUGH THE PERIOD
...SUPPORTIVE OF BOTH SUPERCELLS AND ORGANIZED MESOSCALE CONVECTIVE
SYSTEMS.
AT LEAST A COUPLE OF ZONES OF ENHANCED LOWER/MID TROPOSPHERIC WARM
ADVECTION MAY CONTRIBUTE TO THE INITIATION OF NEW STORMS BY LATE
AFTERNOON...ONE ACROSS NORTH CENTRAL/NORTHEAST KANSAS INTO SOUTH
CENTRAL AND SOUTHEAST NEBRASKA...AND ANOTHER ACROSS WESTERN INTO
CENTRAL SOUTH DAKOTA. STRONGEST STORMS ARE EXPECTED TO BE CAPABLE
OF PRODUCING AT LEAST LARGE HAIL...WITH LOCALLY DAMAGING WIND GUSTS
ALSO POSSIBLE.
FORCING ON THE NOSE OF A STRENGTHENING LOW-LEVEL JET MAY MAINTAIN
STORMS...AND PERHAPS CONTRIBUTE TO UPSCALE CONVECTIVE GROWTH ACROSS
PARTS OF NORTHEAST KANSAS/SOUTHEAST NEBRASKA/NORTHWEST MISSOURI AND
SOUTHWEST IOWA WEDNESDAY EVENING. AT THE SAME TIME...MID-LEVEL
COOLING AND FORCING FOR ASCENT IN THE EXIT REGION OF AN EASTWARD
PROPAGATING MID-LEVEL JET STREAK COULD ENHANCE STORMS ACROSS CENTRAL
AND EASTERN SOUTH DAKOTA...PERHAPS INTO AREAS NORTH AND EAST OF THE
MID MISSOURI VALLEY OVERNIGHT.
..KERR.. 08/31/2010
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