Monday, February 16, 2009

DAY2SVR: Nws Storm Prediction Center Norman Ok

ACUS02 KWNS 161729
SWODY2
SPC AC 161727

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1127 AM CST MON FEB 16 2009

VALID 171200Z - 181200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
TO THE WEST OF A BLOCKING UPPER RIDGE NEAR THE CANADIAN
ROCKIES...THE NEXT IN A SERIES OF STRONG SHORT WAVE IMPULSES IS
ALREADY BEGINNING TO DIG SOUTH OF THE ALEUTIANS. MODELS INDICATE
THAT A CONTINUED SOUTHEASTWARD PROGRESSION OF THIS SYSTEM WILL FORCE
THE INCREASINGLY SHEARED REMNANTS OF THE CLOSED LOW...NOW NEAR THE
CALIFORNIA COAST...EASTWARD WITHIN THE PRIMARY BELT OF POLAR
WESTERLIES EXTENDING ACROSS THE CENTRAL/SOUTHERN TIER OF THE UNITED
STATES.

WHILE A CONSIDERABLE PORTION OF THE REMNANT CIRCULATION MAY LINGER
NEAR THE CENTRAL CALIFORNIA COAST THROUGH MUCH OF THE DAY
TUESDAY...AN INITIAL IMPULSE EMANATING FROM THE SYSTEM IS PROGGED TO
ACCELERATE THROUGH A CONFLUENT REGIME ACROSS THE GREAT BASIN AND
CENTRAL ROCKIES INTO THE CENTRAL PLAINS. THEREAFTER...THE LATTER
FEATURE IS EXPECTED TO TURN EAST NORTHEASTWARD THROUGH THE MIDDLE
MISSISSIPPI AND LOWER OHIO VALLEYS...CONTRIBUTING TO THE ONSET OF
MID-LEVEL HEIGHT FALLS ACROSS MUCH OF THE CENTRAL U.S...AHEAD OF A
COLD UPPER VORTEX DIGGING SOUTH OF THE CENTRAL CANADIAN PROVINCES.

ALTHOUGH SOME VARIABILITY EXISTS AMONG THE MODELS CONCERNING THE
DETAILS...GUIDANCE GENERALLY INDICATES THAT THE EVOLVING UPPER
PATTERN WILL BE ACCOMPANIED BY SIGNIFICANT LOW-LEVEL CYCLOGENESIS TO
THE LEE OF THE CENTRAL ROCKIES. AND...AS THE DEEPENING SURFACE LOW
MIGRATES FROM THE CENTRAL PLAINS THROUGH THE MIDDLE MISSISSIPPI
VALLEY...A SUBSTANTIVE RETURN FLOW OF MOISTURE APPEARS LIKELY TO
COMMENCE OFF THE WESTERN GULF OF MEXICO.

...SERN PLAINS THRU LWR MS/OH AND TENNESSEE VALLEYS...
SREF INDICATES THAT THIS MOISTURE RETURN WILL PROBABLY BE
CHARACTERIZED BY PRECIPITABLE WATER ON THE ORDER OF 1.25 INCHES...
WITH A HIGH PROBABILITY OF UPPER 50S/LOWER 60S SURFACE DEW POINTS
SURGING BACK THROUGH MUCH OF THE LOWER MISSISSIPPI VALLEY BY 12Z
WEDNESDAY. THIS IS EXPECTED...HOWEVER...BENEATH A WARMING LOWER/
MID TROPOSPHERIC ENVIRONMENT ASSOCIATED WITH SHORT WAVE RIDING...
WHICH SHOULD SUPPRESS THE DEVELOPMENT OF THUNDERSTORMS THROUGH MUCH
OF THE DAY...AND COULD INHIBIT ACTIVITY THROUGH MUCH OF THE
REMAINDER OF THE PERIOD.

GUIDANCE IS SUGGESTIVE THAT STORMS COULD INITIATE WITHIN A ZONE OF
ENHANCED LOWER/MID-LEVEL WARM ADVECTION ON THE NORTHEASTERN EDGE OF
THE CAP BY THE 18/03-06Z TIME FRAME...IN THE GENERAL VICINITY OF
WESTERN KENTUCKY/TENNESSEE INTO NORTHERN MISSISSIPPI...BEFORE
SPREADING EASTWARD TOWARD THE UPPER TENNESSEE VALLEY. IT IS
POSSIBLE...IN THE PRESENCE OF FAVORABLE DEEP LAYER SHEAR...THAT
SUFFICIENTLY STEEP MID-LEVEL LAPSE RATES AND CAPE MAY DEVELOP FOR
THE RISK FOR HAIL IN STRONGER STORMS...PARTICULARLY AS THE NIGHT
WEARS ON.

CONTINUING LOW-LEVEL MOISTENING AND ASCENT ASSOCIATED WITH LOW-LEVEL
WARM ADVECTION IS EXPECTED TO EVENTUALLY YIELD CAPE OF 500-1000
J/KG...BASED NEAR OR JUST ABOVE THE SURFACE...ACROSS MUCH OF THE
LOWER MISSISSIPPI VALLEY BY 09-12Z WEDNESDAY MORNING. WHILE
MID/UPPER FORCING FOR UPWARD VERTICAL MOTION MAY BE WEAK TO THE
SOUTH OF AN INTENSIFYING /IN EXCESS OF 90 KTS/ 500 MB JET STREAK
ACROSS THE SOUTH CENTRAL PLAINS/OZARK PLATEAU...THERE IS A SIGNAL
AMONG THE MODELS THAT THE CAPPING LAYER MAY BECOME SUPPRESSED ENOUGH
FOR SCATTERED STORM DEVELOPMENT BY THE END OF THE PERIOD. IF THIS
OCCURS...THE ENVIRONMENT ALONG AN AXIS FROM NEAR OR JUST SOUTH OF
THE ARKLATEX INTO NORTHERN MISSISSIPPI/ WESTERN TENNESSEE WILL
BECOME INCREASINGLY FAVORABLE FOR BOUNDARY LAYER...OR NEAR BOUNDARY
LAYER...BASED STORMS. IN THE PRESENCE OF SIZABLE CLOCKWISE CURVED
LOW-LEVEL HODOGRAPHS AND STRONG DEEP LAYER SHEAR...SUPERCELLS ARE
POSSIBLE...PERHAPS WITH A RISK FOR TORNADOES...IN ADDITION TO
HAIL/GUSTY WINDS.

..KERR.. 02/16/2009

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