181
FXUS02 KWBC 211808
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS HYDROMETEOROLOGICAL PREDICTION CENTER CAMP SPRINGS MD
107 PM EST FRI NOV 21 2008
VALID 12Z MON NOV 24 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...WITH NO RESOLUTION PRESENTED BY THE AVAILABLE 12Z
GUIDANCE. 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.
DEEP CYCLONE NEAR THE WEST COAST MID TO LATE NEXT WEEK...
DIVERGENCE WAS SEEN IN THE 12Z GUIDANCE CONCERNING THIS
SYSTEM...WITH THE 12Z CANADIAN MORE OPEN AND PROGRESSIVE WHILE THE
12Z GFS WAS THE FARTHEST WESTWARD. THE 00Z GUIDANCE WAS IN BETTER
AGREEMENT HERE...AND IS IN THE MIDDLE OF THE SPREAD SEEN IN THE
12Z GUIDANCE. WITH THE AMPLIFICATION EXPECTED UPSTREAM ACROSS THE
PACIFIC...THE SYSTEM SHOULD BE DEEPER THAN SEEN IN THE 12Z
CANADIAN. KEPT WITH THE 00Z GFS/ECMWF COMPROMISE HERE.
POSSIBLE DEEP CYCLONE MOVING FROM OFFSHORE CALIFORNIA THROUGH THE
SOUTHWEST INTO THE SOUTHERN PLAINS...
THE 00Z ECMWF IS 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. USING THE NORTHERN STREAM RIDGE ACROSS
NORTHEAST CANADA AS A GUIDANCE...THE SYSTEM IS MOST LIKELY TO
TRACK THROUGH THE MID TO UPPER 40S LATITUDE BETWEEN THE GFS AND
ECMWF SOLUTIONS. ALL THINGS CONSIDERED...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 FOR
MUCH OF THE MEDIUM RANGE PERIOD.
ROTH
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