SWOD48
SPC AC 010959
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0359 AM CST THU JAN 01 2009
VALID 041200Z - 091200Z
...DISCUSSION...
DETERMINISTIC GFS AND ECMWF MODEL RUNS CONTINUE TO DIFFER IN
HANDLING THE LARGE-SCALE PATTERN THIS PERIOD...SPECIFICALLY
PERTAINING TO THE POTENTIAL SEVERE EVENT FROM LATE DAY 5 /MON. 1-5/
THROUGH DAY 6 /TUE. 1-6/.
AN INITIAL FRONT IS FORECAST BY BOTH MODELS TO CROSS THE ERN HALF OF
THE U.S. DAY 4 /SUN. 1-4/...ACCOMPANIED BY LITTLE SEVERE THREAT.
AS THE TRAILING PORTION OF THIS BOUNDARY SAGS INTO THE GULF OF
MEXICO/NRN MEXICO DAY 5...MODELS FORECAST CYCLOGENESIS ALONG THIS
BOUNDARY AS A SRN STREAM UPPER TROUGH CROSSES THE SWRN CONUS/MEXICO.
MODEL DIFFERENCES WITH RESPECT TO THE TIMING OF THIS TROUGH -- AND
ITS POTENTIAL PHASING WITH A NRN STREAM FEATURE -- RESULT IN
SIGNIFICANT DISCREPANCIES IN TERMS OF THE SURFACE PATTERN.
THE ECMWF BEGINS CYCLOGENESIS OVER NRN MEXICO DAY 5...WHICH THEN
SHIFTS NEWD ACROSS THE WRN GULF INTO THE LOWER MS VALLEY THROUGH THE
END OF DAY 5. THE ECMWF THEN TAKES THIS LOW NWD THROUGH THE TN AND
INTO/ACROSS THE OH VALLEY AND GREAT LAKES REGIONS DAY 6...DURING
WHICH TIME A LARGE WARM SECTOR EXPANDS ACROSS THE SRN QUARTER OF THE
CONUS. MEANWHILE...THE GFS DEPICTS INITIAL CYCLOGENESIS OVER THE
WRN GULF...WITH THE LOW THEN MOVING ENEWD ALONG THE GULF COAST
THROUGH THE AFTERNOON DAY 5...AND THEN ON ACROSS GA/SC LATE DAY
5/EARLY DAY 6. WITH THIS LOW TRACK...LITTLE ONSHORE WARM SECTOR
WOULD EXIST...WITH THE EXCEPTION OF SRN GA/FL AND THE ERN CAROLINAS.
ATTM...BOTH MODELS SEEM TO SUGGEST SEVERE POTENTIAL...BUT THE GFS
SEVERE THREAT -- CONFINED MAINLY TO GA/SC/FL -- WOULD PEAK LATE DAY
5/EARLY DAY 6. MEANWHILE...THE PRIMARY SEVERE THREAT ACCORDING TO
THE ECMWF WOULD BEGIN EARLY DAY 6 ACROSS THE LOWER MS/TN VALLEYS AND
CENTRAL GULF COAST REGION...WITH THE FRONT MOVING OFF THE E COAST
EARLY DAY 7 ENDING THE SEVERE POTENTIAL.
THE DETERMINISTIC RUN OF THE GFS REMAINS AN OUTLIER...WITH THE NCEP
MREF MUCH MORE SIMILAR TO THE ECMWF IN TRACKING A LOW INTO THE TN
VALLEY REGION DAY 6. THUS -- CONFIDENCE IS INCREASING THAT A FAIRLY
SUBSTANTIAL SEVERE EVENT MAY OCCUR PRIMARILY DAY 6 /TUE. 1-6/
CENTERED OVER THE CENTRAL GULF COAST REGION. ONCE AGAIN...WILL
REFRAIN FROM ISSUING AN OUTLOOK AREA...WITH THE GFS SOLUTION STILL
DRIVING SOME LACK OF CONFIDENCE IN THE EVENTUAL SCENARIO. IF THE
ECMWF AND MREF SOLUTIONS REMAIN CONSISTENT HOWEVER...EXPECT THE
POSSIBLE INTRODUCTION OF A THREAT AREA IN LATER FORECASTS.
..GOSS.. 01/01/2009
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