463
FXUS02 KWNH 211217
PREEPD
PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
716 AM EST FRI NOV 21 2008
VALID 12Z TUE NOV 25 2008 - 12Z FRI NOV 28 2008
THE MODELS ARE IN GOOD AGREEMENT THROUGH THE MEDIUM RANGE PERIOD
REGARDING THE GENERAL FLOW PATTERN. INCREASING AMPLITUDE IN THE
STEERING FLOW ACROSS THE PACIFIC LEADS TO THE DEVELOPMENT OF A
WESTERN TROUGH BY LATE NEXT WEEK. OTHERWISE...A POSITIVE ANOMALY
NEAR 55N 38W FAVORS TROUGHING OVER MUCH OF EASTERN NORTH
AMERICA...AS WELL AS THE TROUGHING SEEN IN THE NORTHEAST PACIFIC
THROUGH EARLY NEXT WEEK. DETAIL DIFFERENCES ARE SEEN BETWEEN THE
VARIOUS MODELS. A COMPROMISE BETWEEN THE 00Z ECMWF/00Z GFS
APPEARED BEST CONSIDERING THE UNCERTAINTY...AS WELL AS THEIR BREAK
IN CONTINUITY ACROSS THE NORTHEAST QUARTER OF THE CONTINENT. THIS
SOLUTION KEPT REASONABLE CONTINUITY.
POSSIBLE DEEP CYCLONE MOVING FROM OFFSHORE CALIFORNIA THROUGH THE
SOUTHWEST INTO THE SOUTHERN PLAINS...
THE 00Z ECMWF SLOWER WITH THE SYSTEM MOVING THROUGH THE SOUTHWEST
EARLY NEXT WEEK THAN THE OTHER GUIDANCE...WHILE THE 06Z GFS SPED
AHEAD OF THE PACK. THE 00Z GFS IS MOST IN LINE WITH THE 00Z
GEFS/ECMWF ENSEMBLE MEANS. SINCE THE 00Z ECMWF HAS SOME ENSEMBLE
SUPPORT AMONGST ITS OWN ENSEMBLE MEMBERS...FEEL ITS SOLUTION
CANNOT BE IGNORED. THUS...A BLEND OF THE 00Z GFS/00Z ECMWF
APPEARS BEST HERE. OROGRAPHICALLY-FORCED RAIN AND HIGHER
ELEVATION SNOWS ARE EXPECTED TO SPREAD THROUGH SOUTHERN
CALIFORNIA...THE SOUTHWEST...AND THE SOUTHERN ROCKIES AS THIS
SYSTEM PASSES THROUGH WHICH SHOULD HELP ALLEVIATE DRY CONDITIONS
ACROSS THE REGION. AS THE SYSTEM PASSES THROUGH THE SOUTHERN
PLAINS TOWARDS THE MISSISSIPPI VALLEY...IT SHOULD TAP AMPLE GULF
MOISTURE WHICH COULD LEAD TO HEAVY RAINS ACROSS THE
OZARKS/PORTIONS OF THE MID SOUTH MID TO LATE NEXT WEEK.
NORTHEAST MID TO LATE NEXT WEEK...
THE 00Z ECMWF/ITS ENSEMBLE MEAN ARE MORE NORTH/NORTHWEST WITH A
DEEP CYCLONE IN THE NORTHEAST QUARTER OF NORTH AMERICA MID TO LATE
NEXT WEEK WHEN COMPARED TO THE LAST COUPLE GFS RUNS AND THE 00Z
GEFS/NCEP ENSEMBLE MEAN. THIS IS A SIGNIFICANT SWITCH FROM WHAT
WAS SEEN THIS TIME YESTERDAY...SHOWING A BREAK IN CONTINUITY FOR
BOTH THE ECMWF AND GFS...LOWERING CERTAINTY IN EITHER OF THEIR
DETERMINISTIC RUNS. WITH THE GFS/ECMWF SWITCHING PLACES IN
REGARDS TO THE EASTERN CYCLONE TRACK AND THE ENSEMBLE MEAN
SOLUTIONS IN TWO CAMPS...A COMPROMISE BETWEEN THE TWO APPEARS TO
BE THE BEST COURSE OF ACTION FOR THE TIME BEING. THIS SHOULD KEEP
NEW ENGLAND AND THE EASTERN GREAT LAKES SNOWY FROM TUESDAY ONWARD.
ROTH
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