Prognostic Meteorological Discussion
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000
FXUS02 KWBC 191457
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1057 AM EDT FRI SEP 19 2014

VALID 12Z MON SEP 22 2014 - 12Z FRI SEP 26 2014

...OVERVIEW AND PREFERENCES...

THE MEDIUM RANGE WILL BE CHARACTERIZED BY ANOTHER COLD FRONT
MOVING ACROSS THE EAST EARLY IN THE FORECAST...WITH HIGH PRESSURE
MOVING IN AND THEN BEING REINFORCED THROUGH DAY 7/FRIDAY. AN UPPER
TROUGH MOVING ACROSS THE NORTHEAST US ON DAYS 3 TO 5/MONDAY TO
WEDNESDAY... WILL LIFT NORTHEASTWARD INTO EASTERN CANADA BY DAY
7/FRIDAY.

ACROSS THE REST OF THE NATION...LARGE CHANGES WILL BE UNDERWAY AS
A DEEPENING TROUGH TAKES HOLD ALONG THE WEST COAST.  ALTHOUGH
THERE IS A MINOR UPPER TROUGH  EXPECTED TO MOVE EAST NORTHEASTWARD
WITHIN THE MEAN RIDGE FROM THE GREAT BASIN ACROSS THE NORTHERN
ROCKIES AND NORTHERN PLAINS STATES BY DAY 5/WEDNESDAY THAT THEN
GETS SHEARED ALONG THE US CANADIAN BORDER...A LARGE UPPER LEVEL
RIDGE IS EXPECTED TO EXPAND ACROSS A WIDE AREA OF THE NATION LATE
IN THE FORECAST WITH THE EXCEPTION OF THE WEST.

IN GENERAL...THE OPERATIONAL MODELS ARE IN VERY GOOD AGREEMENT
WITH THE ENSEMBLE MEANS ON DAY 3/MONDAY WITH THE SLIGHT EXCEPTION
THAT THE OPERATIONAL RUNS SUCH AS THE 00Z ECMWF HAS SLIGHT MORE
DETAIL/DEPTH WITH THE EASTERN TROUGH. BY DAY 4...THERE CONTINUES
TO BE FINE AGREEMENT ALTHOUGH THE 00Z CANADIAN APPEARS WAY TOO
AMPLIFIED WITH A TROUGH OVER THE EAST. THIS AGREEMENT CONTINUES
THROUGH WEDNESDAY/DAY 5. BY DAY 6/THURSDAY...THE OPERATIONAL AND
ENSEMBLE CANADIAN RUNS VEER QUITE FAR FROM THEIR RESPECTIVE
ECMWF/GFS/GEFS MEANS WHILE ON DAY 7...LARGER DIFFERENCES START TO
SHOW UP IN BOTH THE OPERATIONAL RUNS AND MEANS. TAKING THIS
INFORMATION INTO ACCOUNT...A BLEND OF THE 00Z ECMWF/ECMWF ENSEMBLE
MEAN AND THE 06Z GFS/GEFS MEAN WERE ALL USED TO GENERATE THE
FORECAST WITH THE OPERATIONAL RUNS CONTRIBUTING MORE TO THE BLENDS
THROUGH DAY 5 WHILE THE ENSEMBLE MEANS HAD MORE INFLUENCE BY DAY
7.  IN GENERAL...THE LARGEST DIFFERENCES ARE OBSERVED LATER IN THE
FORECAST WITH THE WESTERN TROUGH BUT IN GENERAL...THIS WAS NOT A
DIFFICULT FORECAST TO MAKE.

...SENSIBLE WEATHER HIGHLIGHTS...

WITH A COLD FRONT APPROACHING THE EAST COAST ON MONDAY/DAY
3...SHOWERS ARE LIKELY FROM THE MIDDLE ATLANTIC STATES INTO THE
NORTHEAST BUT THE FRONT LOSES ITS MOISTURE SOURCE IN THE
SOUTHEAST. THE WEAK TROUGH MOVING WITHIN THE RIDGE FROM THE GREAT
BASIN TO THE NORTHERN PLAINS WILL PRODUCE SCATTERED SHOWERS AND
THUNDERSTORMS IN THOSE REGIONS AS IT MOVES SLOWLY EAST
NORTHEASTWARD TOWARD THE NORTHERN PLAINS BEFORE WEAKENING ON
THURSDAY INTO FRIDAY.  COMMENSURATELY...THE SHOWER ACTIVITY WILL
LIKELY DROP OFF AS WELL.  THIS REGION SHOULD SEE RELATIVELY WARM
CONDITIONS ALTHOUGH CLOUDS WILL LIKELY TO KEEP AFTERNOON
TEMPERATURES DOWN. IN THE WEST...COOLER AIR AND AN INCREASED
CHANCE OF RAIN AND SHOWERS ARE EXPECTED BY MIDWEEK AS A RATHER
LARGE OCEANIC STORM TAKES UP RESIDENCE OFF THE NORTHWEST COAST.

KOCIN

$$





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