MESOSCALE DISCUSSION 0163
NWS STORM PREDICTION CENTER NORMAN OK
1216 PM CST FRI FEB 27 2009
AREAS AFFECTED...PARTS OF SRN AR....N CNTRL MS INTO W CNTRL AL
CONCERNING...SEVERE THUNDERSTORM WATCH 37...
VALID 271816Z - 271945Z
THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 37
CONTINUES.
TRENDS ARE BEING MONITORED FOR THE POSSIBILITY OF INCREASING
TORNADIC POTENTIAL...A NEW TORNADO WATCH WILL LIKELY BE ISSUED SOON.
ATTEMPTS AT DEEP CONVECTIVE DEVELOPMENT ALONG A LOW-LEVEL CONFLUENT
ZONE ACROSS SOUTHEAST MISSISSIPPI INTO WEST CENTRAL ALABAMA HAVE
BEEN SUPPRESSED BY CAPPING ELEVATED WARM LAYER. THIS MAY REMAIN THE
CASE...THOUGH THE MOIST BOUNDARY LAYER CONTINUES TO WARM WITH
INSOLATION.
STRONGER STORMS REMAIN FOCUSED ALONG A WEST-NORTHWEST TO EAST-
SOUTHEAST MID-LEVEL THERMAL GRADIENT AT THE EDGE OF THE WARM
LAYER...WHERE LOWER/MID TROPOSPHERIC WARM ADVECTION IS CONTRIBUTING
TO LARGE-SCALE ASCENT. THE INFLUENCE OF A RESIDUAL STABLE LAYER
NEAR THE SURFACE CONTINUES TO PROVIDE UNCERTAINTY CONCERNING THE
SEVERE THREAT BEYOND THE RISK FOR LARGE HAIL...PARTICULARLY IN THE
NEAR TERM. HOWEVER...IN RESPONSE TO THE DIGGING UPSTREAM
TROUGH...THERE HAS BEEN A TENDENCY FOR A NORTHWARD SHIFT OF AN
ONGOING EVOLVING CONVECTIVE BAND...WITH NEW CELLS DEVELOPING JUST TO
ITS SOUTH. AND...THE MODIFICATION OF THE BOUNDARY LAYER WITHIN A
NEAR SURFACE BAROCLINIC ZONE ASSOCIATED WITH THE RAIN COOLED AIR MAY
BE ENOUGH TO SUPPORT INCREASING TORNADIC POTENTIAL THROUGH THE
AFTERNOON. MODELS SUGGEST SOME STRENGTHENING OF SOUTHWESTERLY 850
MB FLOW THROUGH THE AFTERNOON ...WHICH SHOULD YIELD INCREASINGLY
LARGE CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS THROUGH THE 20-22Z TIME
FRAME.
..KERR.. 02/27/2009
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