030
ACUS48 KWNS 200945
SWOD48
SPC AC 200943
DAY 4-8 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0343 AM CST MON JAN 20 2020
VALID 231200Z - 281200Z
..DISCUSSION
MEDIUM-RANGE MODEL SOLUTIONS HAVE COME INTO BETTER AGREEMENT
RECENTLY, WITH THE GFS, ECMWF, AND NAM VERY SIMILAR WITH RESPECT TO
THE BROAD PATTERN OVER THE U.S. AT 84 HOURS.
BEYOND DAY 3 AND INTO THE MEDIUM RANGE, THE GFS AND ECMWF DO BEGIN
TO MODERATELY DIVERGE, WITH RESPECT TO PROGRESSION AND EVOLUTION OF
CENTRAL U.S. UPPER TROUGHING, AS IT SHIFTS EASTWARD ACROSS THE MID
MISSISSIPPI AND INTO THE TENNESSEE/OHIO VALLEYS AND EVOLVES INTO A
CLOSED LOW THROUGH THE END OF DAY 4 (THURSDAY) AND INTO DAY 5
(FRIDAY).
BY SUNSET FRIDAY, THE CLOSED LOW IS DEPICTED BY THE GFS TO LIE NEAR
THE ILLINOIS/INDIANA BORDER, WHILE THE ECMWF CENTERS THE LOW OVER
NORTHERN ALABAMA. AS A RESULT, THE GFS PLACES THE MAIN/ASSOCIATED
SURFACE LOW MUCH FARTHER NORTH (ILLINOIS/INDIANA) THAN THE EURO
(WHICH DEPICTS THE LOW OVER THE SAVANNAH RIVER AFTER SUNSET FRIDAY).
IN EITHER CASE HOWEVER, AN INCOMPLETELY MODIFIED GULF BOUNDARY LAYER
IS EXPECTED, DUE TO RECENT POLAR SURFACE HIGH INTRUSION. THIS --
COMBINED WITH WEAK SURFACE REFLECTION OF THE UPPER SYSTEM AND THUS
WEAK NORTHWARD THETA-E RETURN -- SUGGEST THAT ANY SEVERE-WEATHER
RISK WOULD BE LOW, ACROSS THE REGION. AS SUCH, NO RISK AREAS APPEAR
TO BE NECESSARY AT THIS TIME.
WITH A COLD FRONT ASSOCIATED WITH THIS SYSTEM PROGGED NEAR THE
ATLANTIC COAST AT THE START OF DAY 6, WHILE HIGH PRESSURE SETTLES
ACROSS THE CENTRAL AND EASTERN U.S. IN ITS WAKE, CONVECTIVE
POTENTIAL WILL DIMINISH OVER THE COUNTRY. WHILE A PACIFIC TROUGH IS
THEN EXPECTED TO MOVE ONSHORE OVER THE WEST DAY 7, AND ACROSS THE
ROCKIES DAY 8, DIFFERENCES AMONGST THE MODELS WITH THE EVOLUTION OF
THIS FEATURE PRECLUDE ANY ASSESSMENT OF CONVECTIVE POTENTIAL AT THIS
TIME.
..GOSS.. 01/20/2020
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