SWOD48
SPC AC 180858
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0358 AM CDT FRI MAR 18 2011
VALID 211200Z - 261200Z
...PREDICTABILITY TOO LOW TO DELINEATE A SEVERE RISK AREA...
THE PRESENCE OF STEEP LAPSE RATES AND STRENGTHENING SHEAR WILL
UNDOUBTEDLY CONTRIBUTE TO AT LEAST SOME INCREASE IN SEVERE POTENTIAL
ACROSS PARTS OF THE CENTRAL/SOUTHERN PLAINS INTO THE MIDDLE
MISSISSIPPI VALLEY EARLY NEXT WEEK...WITH THE APPROACH OF THE
SIGNIFICANT UPPER IMPULSE EMERGING FROM THE EASTERN PACIFIC.
HOWEVER...MEDIUM RANGE MODELS CONTINUE TO SUGGEST THAT THE QUALITY
OF THE LOW-LEVEL MOISTURE RETURN MAY REMAIN A LIMITING FACTOR WITH
RESPECT TO THE AREAL COVERAGE OF THIS THREAT. ANY SIGNIFICANT
SEVERE WEATHER RISK SEEMS LIKELY TO REMAIN CONFINED TO SMALLER SCALE
FORCING THAT IS TOO UNPREDICTABLE WITH REGARD TO INTENSITY AND
LOCATION AT THIS EXTENDED TIME RANGE.
LATEST GUIDANCE DOES APPEAR TO EXHIBIT A GREATER SIGNAL CONCERNING
THE POTENTIAL FOR A MORE WIDESPREAD STRONG/SEVERE CONVECTIVE EVENT
FROM UPPER PORTIONS OF THE LOWER MISSISSIPPI VALLEY THROUGH THE
LOWER OHIO AND TENNESSEE VALLEYS BY WEDNESDAY...AS THE UPPER IMPULSE
AND ASSOCIATED SURFACE WAVE DEVELOP EASTWARD. THIS MAY INCLUDE A
FAST MOVING SQUALL LINE WITH POTENTIAL FOR DAMAGING WIND
GUSTS...THAT COULD SPREAD INTO SOUTHERN MID ATLANTIC COASTAL AREAS
BY THURSDAY. HOWEVER...THIS OCCURS AS THE SPREAD WITHIN THE MODEL
ENSEMBLES BECOMES INCREASINGLY LARGE...AND CONFIDENCE IS TOO LOW TO
DELINEATE AN AREA AT THE PRESENT TIME.
..KERR.. 03/18/2011
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