DAY48SVR: Nws Storm Prediction Center Norman Ok

ACUS48 KWNS 180856
SWOD48
SPC AC 180856

DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0356 AM CDT WED APR 18 2007

VALID 211200Z - 261200Z

..DISCUSSION...
GFS AND ECMWF ARE REMARKABLY CONSISTENT IN HANDLING THE STRONG
SHORT-WAVE TROUGH EXITING THE ROCKIES/ENTERING THE PLAINS DAY 4
/SAT. APR. 21/. NOT ONLY ARE THE MODEL SOLUTIONS FROM THE CURRENT
RUN EXTREMELY SIMILAR...BUT A GREAT DEAL OF MODEL CONSISTENCY HAS
EXISTED FOR THE PAST SEVERAL DAYS IN DEPICTING THIS FEATURE MOVING
INTO THE CENTRAL CONUS FOR SAT. APR. 21.

THE BIGGEST NEGATIVE ATTM APPEARS TO BE THE DEGREE OF BOUNDARY-LAYER
MOISTURE RETURN...AS TRAJECTORIES OFF THE GULF/INTO TX REMAIN
ELY/ESELY AROUND A LARGE HIGH OVER THE ERN HALF OF THE CONUS/GULF OF
MEXICO. HAVING SAID THIS...CONFIDENCE REMAINS HIGH THAT THE
STRENGTH OF THE EJECTING TROUGH AND ASSOCIATED WIND FIELD WILL
SUPPORT A FAIRLY SIGNIFICANT SEVERE EVENT DESPITE THE POSSIBILITY OF
RELATIVELY LIMITED INSTABILITY. THEREFORE...WILL MAINTAIN A THREAT
FOR SAT. /DAY 4/ ACROSS A LARGE PORTION OF THE PLAINS.

THE POSSIBLE LACK OF MOISTURE MAY BECOME MORE OF A LIMITING FACTOR
FOR DAY 5...AS THE UPPER TROUGH EJECTS NEWD ACROSS THE PLAINS AND
EVENTUALLY ACROSS THE UPPER GREAT LAKES REGION. WHILE SOME SEVERE
POTENTIAL WILL EXIST INTO THE MID/UPPER MS AND LOWER OH VALLEYS AND
POSSIBLY THE UPPER GREAT LAKES...OVERALL DEGREE OF SEVERE MAY BE
LIMITED DUE TO AN OVERALL LACK OF FAVORABLE INSTABILITY.
THEREFORE...WILL NOT HIGHLIGHT THE POTENTIAL FOR A SIGNIFICANT EVENT
FOR DAY 5 ATTM.

MODEL DIVERGENCE INCREASES -- AT LEAST WITH RESPECT TO TIMING -- FOR
DAYS 6-8. WHILE BOTH MODELS BRING A STRONG TROUGH/CLOSED LOW INTO
THE CENTRAL AND SRN PLAINS DURING THIS TIME FRAME...THE GFS IS CLOSE
TO 24 HOURS FASTER WITH THIS FEATURE THAN THE ECMWF. THUS...WILL
REFRAIN ATTM FROM HIGHLIGHTING THE SEVERE POTENTIAL ASSOCIATED WITH
THIS FEATURE ATTM...THOUGH CONFIDENCE IS INCREASING THAT A SEVERE
EVENT WILL INDEED OCCUR SOMETIME IN THE DAY 6-8 TIME FRAME OVER THE
SRN PLAINS.

.GOSS.. 04/18/2007

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