Prognostic Meteorological Discussion
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FXUS02 KWBC 031507
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1106 AM EDT THU SEP 03 2015

VALID 12Z SUN SEP 06 2015 - 12Z THU SEP 10 2015


WHILE THERE IS STILL PRETTY GOOD AGREEMENT OVER NORTH AMERICA IN
THE MEDIUM RANGE FORECAST...THERE IS POSSIBLE TROUBLE AHEAD AS THE
FORECASTS OVER THE PACIFIC VARY FAIRLY WIDELY...AND THOSE EFFECTS
COULD BE FELT DOWNSTREAM FOR THE FORECASTS OVER THE NEXT SEVERAL
DAYS.  HOWEVER...USING SOME CONTINUITY AS A GUIDE...THE 06Z GEFS
MEAN STARTED TO DEVIATE FROM PREVIOUS FORECASTS AND GENERATED WHAT
APPEAR TO BE SOMEWHAT OF AN OUTLIER FORECAST OVER THE NORTHEAST
PACIFIC INTO WESTERN NORTH AMERICA...SO WAS DROPPED IN FAVOR OF
THE 00Z GEFS MEAN...WHICH HAS SOME PRETTY DECENT AGREEMENT WITH
THE 00Z ECMWF ENSEMBLE MEAN.  WITH THE 00Z ECMWF SOMEWHAT IN LINE
WITH THE MEANS...ESPECIALLY EARLY IN THE FORECAST...FAVORED THAT
OPERATIONAL RUN IN THE BLENDS VERSUS THE 00Z GFS...AND ESPECIALLY
THE 06Z GFS...ON DAYS 5 AND 6/TUESDAY AND WEDNESDAY.  NO PROBLEM
IN GENERAL ON DAYS 3 AND 4/SUNDAY AND MONDAY...WITH MANY DIFFERENT
BLENDS OF OPERATIONAL/ENSEMBLE MEANS WOULD BE SUFFICIENT.  IN
GENERAL...THE 00Z GEFS MEAN/ECMWF ENSEMBLE MEANS BOTH SEEMED TO
REPRESENT THE LARGE SCALE MOTION AND THE FORECASTS WERE GENERALLY
BASED ON BOTH...WITH DETAILS PROVIDED BOTH BY THE 00Z GFS/ECMWF
THROUGH DAY 4...THE 00Z ECMWF THROUGH DAY 6 AND MOSTLY THE MEANS
ON DAY 7.

THE MEDIUM RANGE BEGINS WITH THE DEEP WESTERN TROUGH LIFTING
NORTHEASTWARD FROM THE NORTHERN ROCKIES INTO SOUTH CENTRAL CANADA
WITH SIGNIFICANT RAINS/MOUNTAIN SNOWS ENDING EARLY ON.  AS THIS
SYSTEM MOVES INTO SOUTH CENTRAL CANADA...ITS TRAILING COLD FRONT
WILL USHER IN COOLER WEATHER ACROSS THE NORTHERN PLAINS AND UPPER
MISSISSIPPI VALLEY ON DAY 4/MONDAY.  MEANWHILE...A BROAD UPPER LOW
WILL REMAIN OVER AND OFF THE SOUTHEAST COAST...WITH A CENTER OF
LOW PRESSURE DEVELOPING OVER THE WARM WATERS OF THE ATLANTIC AND
APPEARS IN THE FORECAST NEAR OR OFF THE COAST THROUGH AT LEAST DAY
6/WEDNESDAY.  BY DAY 5/TUESDAY...THE FRONT CONTINUES EASTWARD
ACROSS THE MIDWEST WITH THE ENSEMBLES SHOWING A POSSIBLE WEAK WAVE
ACROSS THE PLAINS WHILE THE FRONT STALLS THROUGH THE MID
MISSISSIPPI VALLEY ON DAY 6.  THE COLD FRONT REACHES THE EAST
COAST BY DAY 7/THURSDAY. WITH THE EMPHASIS ON THE SOLUTIONS OF THE
00Z ECMWF AND GEFS ENSEMBLE MEANS...THE TREND TOWARD A TROUGH OVER
THE NORTHWEST FAVORS THE MOVEMENT OF A COLD FRONT AND COOLER
TEMPERATURES AGAIN ACROSS THE NORTHWEST CORNER OF THE COUNTRY.

PRECIPITATION WILL BE ENDING ACROSS THE NORTHERN ROCKIES ON DAY
3/SUNDAY AND WILL FOCUS ALONG THE FRONTAL BOUNDARY MOVING EASTWARD
IN THE NEXT SEVERAL DAYS...WITH SOME LIKELIHOOD OF SIGNIFICANT QPF
AS THE FRONT STALLS AND A POSSIBLE WAVE DEVELOPS ACROSS THE
PLAINS.  THE BROAD WEAK UPPER LOW OVER THE SOUTHEAST WILL CONTINUE
CHANCES FOR SCATTERED SHOWERS AND THUNDERSHOWERS THERE THROUGH THE
PERIOD...ESPECIALLY ACROSS FLORIDA.


KOCIN

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