Prognostic Meteorological Discussion
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000
FXUS02 KWBC 021545
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1143 AM EDT WED SEP 02 2015

VALID 12Z SAT SEP 05 2015 - 12Z WED SEP 09 2015


THERE IS GOOD CONTINUITY IN TODAYS FORECAST AT LEAST OVER THE US
AND SOUTHERN CANADA AS THE DEEP TROUGH OVER THE WEST COAST IS
FORECAST TO LIFT NORTHEASTWARD INTO SOUTH CENTRAL
CANADA...FLATTENING THE ANOMALOUS UPPER HIGH OVER THE NORTHEAST
TOWARD THE END OF THE FORECAST.  UPPER TROUGHING AND A WEAKNESS IN
THE UPPER FLOW IS FORECAST TO PERSIST OVER THE SOUTHEAST THROUGH
THE PERIOD WHILE THE UPPER RIDGE SHRINKS AND RETROGRADES FROM THE
GULF COAST TO THE SOUTHWEST.  A POTENTIAL MAIN PLAYER IN THE
FORECAST LIES OUTSIDE THE US AS HURRICANE IGNACIO HEADS
NORTHEASTWARD TOWARD ALASKA AND IS LIKELY TO INTERACT IN SOME WAY
WITH A TROUGH OVER THE STATE.  HOWEVER...THAT POTENTIAL IS REALLY
IN THE END OF THE FORECAST AND WILL LIKELY HAVE LITTLE IMPACT IN
THE FORECAST PERIOD COVERED HERE.

BOTH THE 00Z ECWMF AND 06Z GFS WERE QUITE SIMILAR TO EACH OTHER
AND WITH RESPECT TO THE ENSEMBLE MEANS THROUGH DAY 6...WHICH IS
RELATIVELY UNUSUAL AND ALLOWED A LARGER PORTION OF THE OPERATIONAL
RUNS TO BE USED IN THE BLEND FOR THE FORECAST THROUGH DAY 6.
THEREFORE...THE FORECAST TODAY CAN BE CONSIDERED ABOVE AVERAGE IN
CONFIDENCE THROUGH MUCH OF THE FORECAST.

EARLY IN THE FORECAST...THE MOVEMENT OF THE DEEP TROUGH WILL
LIKELY PRODUCE SIGNIFICANT QPF OVER THE NORTHWEST QUARTER OF THE
NATION...WITH QUITE COOL TEMPERATURES ESPECIALLY ALOFT...ALLOWING
FOR SNOW TO FALL AT THE HIGHER ELEVATIONS IN THE NORTHWEST FROM
OREGON AND WASHINGTON INTO IDAHO AND MONTANA. SIGNIFICANT QPF IS
POSSIBLE IN MONTANA.  VERY WARM AIR WILL STREAM NORTHEASTWARD
ACROSS THE PLAINS OUT AHEAD OF THE FRONT AND SOME SEVERE WEATHER
IS POSSIBLE.  EVENTUALLY THE FRONT WILL CONTINUE EASTWARD BUT LOSE
ITS SOUTHERN SUPPORT AS THE TROUGH LIFTS NORTHEASTWARD POSSIBLY
REACHING THE OHIO VALLEY AND NORTHEAST BY THE END OF THE FORECAST.
 HIGH PRESSURE WILL BUILD ACROSS THE EAST COAST AND RESULT IN
COMFORTABLE TEMPERATURES BEFORE THE HIGH MOVES OFFSHORE AND A
RETURN TO WARMER TEMPERATURES IS LIKELY. EASTERLY FLOW AND A WEAK
BOUNDARY ACROSS THE SOUTHEAST/GULF COULD RESULT IN SCATTERED
SHOWERS/THUNDERSHOWERS THROUGHOUT THE PERIOD.

KOCIN

$$





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