DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1252 AM CDT SAT JUL 17 2010
 |
VALID 171200Z - 181200Z
...THERE IS A MDT RISK OF SVR TSTMS LATE THIS AFTERNOON AND EVENING
ACROSS PARTS OF SOUTHEASTERN NORTH DAKOTA/EASTERN SOUTH
DAKOTA...MUCH OF CENTRAL AND SOUTHERN MINNESOTA...NORTHERN IOWA AND
WESTERN WISCONSIN...
...THERE IS A SLGT RISK OF SVR TSTMS SURROUNDING THE MODERATE RISK
AREA ACROSS EASTERN PORTIONS OF THE NORTHERN PLAINS AND MUCH OF THE
UPPER MISSISSIPPI VALLEY...
...THERE IS A SLGT RISK OF SVR TSTMS TODAY ACROSS PARTS OF THE
MID/UPPER OHIO VALLEY INTO THE CENTRAL APPALACHIANS...
...SYNOPSIS...
AS A MORE PROMINENT...ELONGATED MID-LEVEL CIRCULATION CONTINUES TO
PIVOT IN A GENERAL WESTERLY DIRECTION ACROSS NORTHEASTERN
CANADA...MODELS INDICATE THAT THE CLOSED LOW NEAR JAMES BAY WILL DIG
ACROSS SOUTHERN QUEBEC BEFORE TURNING EASTWARD TOWARD THE GULF OF
ST. LAWRENCE/CANADIAN MARITIMES LATER TODAY/TONIGHT. AS THIS
OCCURS...BROAD UPPER TROUGHING TO ITS SOUTH WILL LIKELY SHIFT FROM
THE GREAT LAKES REGION THROUGH THE NORTHEASTERN STATES. AT THE SAME
TIME...ANOTHER SIGNIFICANT AND PROGRESSIVE IMPULSE WITHIN A
LINGERING BELT OF STRONGER WESTERLIES NEAR THE CANADIAN/U.S. BORDER
APPEARS LIKELY TO SUPPRESS UPPER RIDGING ACROSS THE NORTHERN
PLAINS/UPPER MISSISSIPPI VALLEY...AS YET ANOTHER IMPULSE DIGS ACROSS
BRITISH COLUMBIA AND PARTS OF THE PACIFIC NORTHWEST. MEANWHILE...A
SUBTROPICAL HIGH CENTER IS EXPECTED TO REMAIN STRONG ACROSS THE FOUR
CORNERS STATES.
ASSOCIATED WITH THE EVOLVING UPPER PATTERN...A CONTINUED INFLUX OF
MOISTURE FROM THE LOWER LATITUDE EASTERN PACIFIC INTO THE SOUTHERN
PLATEAU/GREAT BASIN AND ROCKIES WILL SUPPORT CONSIDERABLE
THUNDERSTORM ACTIVITY TODAY. WEAK INHIBITION AND SEASONABLY HIGH
MOISTURE CONTENT WILL ALSO LIKELY SUPPORT WIDESPREAD CONVECTIVE
DEVELOPMENT ACROSS THE CENTRAL AND EASTERN GULF STATES INTO THE
CENTRAL AND SOUTHERN APPALACHIANS. AND ADDITIONAL STORMS ARE ALSO
LIKELY IN ASSOCIATION WITH THE SHORT WAVE PERTURBATIONS ACROSS THE
NORTH CENTRAL AND NORTHEASTERN STATES.
...NORTHERN PLAINS INTO THE UPPER MISSISSIPPI VALLEY...
MODELS INDICATE THAT VERY STEEP LAPSE RATES...ASSOCIATED WITH WARM
ELEVATED MIXED LAYER AIR ADVECTING NORTHEAST OF THE CENTRAL
ROCKIES...WILL OVERSPREAD THE REGION TODAY...AHEAD OF THE
APPROACHING SHORT WAVE IMPULSE. COUPLED WITH INCREASING MOISTURE ON
MODEST SOUTHERLY LOW-LEVEL FLOW...CAPE APPEARS LIKELY TO BECOME
QUITE LARGE...ON THE ORDER OF 3000-4000 J/KG...THIS AFTERNOON IN THE
WARM SECTOR OF A SURFACE LOW/FRONTAL WAVE ACCOMPANYING THE UPPER
SYSTEM. AS FAVORABLE LARGE-SCALE FORCING FOR UPWARD VERTICAL
CONTRIBUTES TO WEAKENING INHIBITION...THE DEVELOPMENT OF STORMS IS
EXPECTED ACROSS THE EASTERN DAKOTAS/WESTERN MINNESOTA BY LATE
AFTERNOON.
INITIALLY DISCRETE...AND IN THE PRESENCE OF STRONG DEEP LAYER SHEAR
BENEATH 35-50 KT WEST NORTHWESTERLY 500 MB FLOW...A FEW SUPERCELLS
APPEAR LIKELY...WITH POTENTIAL FOR VERY LARGE HAIL/LOCALIZED STRONG
DOWNBURSTS...AND A FEW TORNADOES. THEREAFTER...A GRADUAL
CONSOLIDATION AND UPSCALE GROWTH INTO A SEVERE MESOSCALE CONVECTIVE
SYSTEM SEEMS PROBABLE BY EARLY EVENING...SPREADING ACROSS MUCH OF
CENTRAL/SOUTHERN MINNESOTA...WHERE A STRENGTHENING SOUTHWESTERLY 850
MB JET /30-40+ KT/ WILL ENHANCE THE DAMAGING WIND POTENTIAL WITH AN
EVOLVING CONVECTIVELY GENERATED SURFACE COLD POOL. THIS THREAT MAY
PERSIST INTO THE OVERNIGHT HOURS...PERHAPS SPREADING THROUGH THE
REMAINDER OF THE UPPER MISSISSIPPI VALLEY REGION...AND SOUTHWARD
INTO AREAS NEAR/EAST OF THE MID MISSOURI VALLEY.
...OHIO VALLEY/CENTRAL APPALACHIANS...
MODELS ARE SUGGESTIVE THAT AN AREA OF ENHANCED MID-LEVEL FORCING FOR
UPWARD VERTICAL MOTION WITHIN THE BROADER SCALE CYCLONIC FLOW WILL
OVERSPREAD THE MID/UPPER OHIO VALLEY REGION INTO THE CENTRAL
APPALACHIANS THIS AFTERNOON...COINCIDENT WITH MODERATELY STRONG
BOUNDARY LAYER DESTABILIZATION DURING THE PEAK HEATING HOURS. FLOW
FIELDS AND SHEAR MAY REMAIN FAIRLY MODEST...BUT THE ENVIRONMENT MAY
BECOME SUPPORTIVE OF A RELATIVE CONCENTRATION OF STRONG/SEVERE
STORMS CAPABLE OF PRODUCING LOCALLY DAMAGING WIND GUSTS.
..KERR/STOPPKOTTE.. 07/17/2010