Thursday, April 23, 2009

DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 230900
SWOD48
SPC AC 230859

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0359 AM CDT THU APR 23 2009

VALID 261200Z - 011200Z

...SEVERE STORMS POSSIBLE FROM PARTS OF THE S CNTRL PLAINS THROUGH
UPPER PORTIONS OF THE MID MS VALLEY INTO THE GREAT LAKES SUNDAY...

MEDIUM RANGE MODELS REMAIN IN REASONABLE AGREEMENT THROUGH THE
COMING WEEKEND...CONCERNING AT LEAST THE BASICS OF THE LARGE-SCALE
PATTERN EVOLUTION. WITHIN THE PREVAILING SPLIT UPPER FLOW...A
SIGNIFICANT UPPER IMPULSE IS PROGGED TO CONTINUE TO LIFT OUT OF THE
WESTERN TROUGH THROUGH THE UPPER MISSISSIPPI VALLEY/GREAT LAKES
REGION SUNDAY/SUNDAY NIGHT. THIS IS EXPECTED TO MAINTAIN STRONG
LIFT AND DEEP LAYER SHEAR NEAR A SLOW MOVING OR STALLED FRONTAL ZONE
EXTENDING FROM THE GREAT LAKES REGION THROUGH THE SOUTH CENTRAL HIGH
PLAINS. A NARROWING TONGUE OF STEEP MID-LEVEL LAPSE RATES WILL
PROBABLY LINGER AT LEAST ONE MORE DAY ON THE WESTERN PERIPHERY OF A
STRONG LOWER/MID TROPOSPHERIC RIDGE CENTERED NEAR SOUTH ATLANTIC
COASTAL AREAS. AS A MOIST GULF RETURN FLOW CONTINUES...THIS SHOULD
CONTRIBUTE TO SUFFICIENT INSTABILITY TO SUPPORT THE RISK FOR SEVERE
STORMS. ACTIVITY ALONG THE FRONT IS EXPECTED TO GENERALLY ORGANIZE
INTO LINES/CLUSTERS ...WITH DISCRETE SUPERCELLULAR STORMS PROBABLY
CONFINED TO THE VICINITY OF THE SOUTH CENTRAL HIGH PLAINS DRY LINE
LATE SUNDAY AFTERNOON/EVENING. THEREAFTER...LARGE MODEL SPREAD AND
THE UNCERTAIN LINGERING INFLUENCE OF WIDESPREAD CONVECTION PRECLUDES
CONFIDENTLY DETERMINING THE SEVERE POTENTIAL THROUGH THE REMAINDER
OF THE PERIOD.

..KERR.. 04/23/2009

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