Thursday, March 01, 2007

HIGH RISK

The Storm Prediction Center has placed most of Alabama and parts of eastern Mississippi under a rare HIGH RISK of severe weather for today.

A "high risk" means that at least 20 tornadoes with at least two rated EF3 or greater are expected in a 50,000 mile area (the State of Alabama is roughly 52,000 square miles).

Here is an exerpt from the SPC outlook.


DAY 1 CONVECTIVE OUTLOOK NWS STORM PREDICTION CENTER NORMAN OK 1213 AM CST THU MAR 01 2007

VALID 011200Z - 021200Z

...THERE IS A HIGH RISK OF SVR TSTMS TODAY ACROSS PARTS OF ERN MISSISSIPPI AND ALABAMA

...WHERE POTENTIAL EXISTS FOR AN OUTBREAK OF TORNADOES...SOME POSSIBLY STRONG OR VIOLENT....

...THERE IS A MDT RISK OF SVR TSTMS SURROUNDING THE HIGH RISK AREA...ACROSS MUCH OF THE LOWER HALF OF THE MISSISSIPPI VALLEY AND GULF/SOUTH ATLANTIC COAST STATES....

...THERE IS A SLGT RISK OF SVR TSTMS TODAY/TONIGHT ACROSS A LARGE PORTION OF THE CENTRAL/EASTERN STATES....

LARGE SCALE PATTERN ACROSS THE U.S. DURING THIS FORECAST PERIOD WILL BECOME DOMINATED BY A DEEP CYCLONE NOW DEVELOPING ACROSS THE CENTRAL PLAINS...IN RESPONSE TO AN INTENSE MID/UPPER JET STREAK NOSING NORTHEAST OF THE SOUTHERN ROCKIES. UPPER JET CORE IS PROGGED TO SHIFT THROUGH THE SOUTHERN PLAINS/NORTHERN GULF STATES AND SOUTHERN APPALACHIANS TODAY THROUGH EARLY FRIDAY...WITH SURFACE CYCLONE GRADUALLY OCCLUDING AS IT LIFTS THROUGH THE UPPER MISSISSIPPI VALLEY/UPPER GREAT LAKES REGION. AS THIS OCCURS...A COLD FRONT WILL SURGE EAST OF THE MISSISSIPPI VALLEY...LIKELY REACHING ATLANTIC COASTAL AREAS BY 12Z FRIDAY. AND...MODELS SUGGEST SECONDARY SURFACE CYCLOGENESIS MAY OCCUR FROM THE LEE OF THE NORTH CENTRAL APPALACHIANS INTO NORTHERN MID ATLANTIC COASTAL AREAS.

ALTHOUGH GULF RETURN FLOW MAY NOT BECOME OF SUFFICIENT QUALITY TO SUPPORT WIDESPREAD SIGNIFICANT DESTABILIZATION ACROSS THE CENTRAL AND EASTERN STATES...IT SHOULD BE ADEQUATE ENOUGH TO SUPPORT AN EXTENSIVE CONVECTIVE OUTBREAK...GIVEN FAVORABLE LARGE SCALE FORCING FOR UPWARD VERTICAL MOTION. STRONG WIND FIELDS/SHEAR WILL SUPPORT SEVERE POTENTIAL ACROSS A BROAD AREA...INCLUDING A RISK OF STRONG TORNADOES AND STRONG STRAIGHT LINE DAMAGING WINDS... PARTICULARLY ACROSS PARTS OF THE GULF INTO SOUTH ATLANTIC COAST STATES.

...PARTS OF THE CNTRL GULF STATES/TENNESSEE VALLEY... WHILE STRONGER MID-LEVEL FORCING SHIFTS NORTHEAST OF THE LOWER MISSOURI/MIDDLE MISSISSIPPI VALLEY DURING THE MIDDAY AND AFTERNOON HOURS...LARGE-SCALE ASCENT IS EXPECTED TO WEAKEN CAP SUFFICIENTLY FOR MORE SCATTERED CONVECTIVE DEVELOPMENT EAST OF THE LOWER MISSISSIPPI VALLEY. THIS MAY COMMENCE AS EARLY AS THE 15-18Z TIME FRAME ACROSS PARTS OF WESTERN TENNESSEE/MISSISSIPPI...BEFORE SPREADING ACROSS ALABAMA DURING THE PEAK AFTERNOON HEATING HOURS. WITH BOUNDARY LAYER DEW POINTS CLIMBING THROUGH THE MID 60S CONTRIBUTING TO MIXED LAYER CAPE OF 500 TO 1000 J/KG...SUPERCELLS ROOTED NEAR THE SURFACE WILL BY ACCOMPANIED BY A RELATIVELY HIGH RISK OF TORNADOES. LARGE...CLOCKWISE CURVED HODOGRAPHS BENEATH A STRONG UPPER JET WILL BE SUPPORTIVE OF A FEW LONG-LIVED/LONG TRACK SUPERCELLS WITH STRONG OR VIOLENT TORNADOES.

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