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340
FXUS02 KWNH 290443
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1242 AM EDT FRI AUG 29 2014

VALID 12Z MON SEP 01 2014 - 12Z FRI SEP 05 2014

...OVERVIEW AND GUIDANCE PREFERENCES...

IN A CHANGE FROM RECENT MONTHS... RIDGING IS FORECAST TO BUILD
INTO THE EASTERN THIRD OF THE CONUS NEXT WEEK WHILE TROUGHING IS
FAVORED IN THE PAC NW TOWARD THE HIGH PLAINS. FARTHER UPSTREAM...
A DEEP UPPER LOW SHOULD GRAZE NORTHERN ALASKA AND HELP SEND ENERGY
SOUTHEASTWARD THROUGH THE GULF OF ALASKA TOWARD WA/BC. THE
MODELS/ENSEMBLES SHOW THE MOST SENSITIVITY TO THE DETAILS HERE...
WHICH TRANSLATE TO MOSTLY TIMING DIFFERENCES DOWNSTREAM OVER THE
NORTHERN ROCKIES BY THE END OF NEXT WEEK. ENSEMBLE MEANS ARE
LARGELY IN AGREEMENT THOUGH THE 18Z GEFS OUTPACES THE 12Z ECENS
MEAN BY THURS-FRI NEXT WEEK... IN TYPICAL FASHION. USED A BLEND OF
THE RECENT 12Z/18Z ECMWF/GFS DETERMINISTIC AND ENSEMBLE GUIDANCE
MON-TUE/D3-4 BEFORE DROPPING THE GFS AS IT MAY BE TOO EMPHATIC TO
BRING A SFC WAVE INTO THE GREAT LAKES IN LIGHT OF THE ENSEMBLES
AND PREVIOUS ECMWF RUNS. SPLIT THE ECENS-GEFS DIFFERENCES IN THE
PAC NW BY FRI/D7 WHICH ALIGNS NEAR THE 12Z NAEFS MEAN.


...SENSIBLE WEATHER HIGHLIGHTS...

TEMPERATURES SHOULD FALL BELOW AVERAGE IN THE NORTHWEST THROUGH
MONTANA TOWARD THE HIGH PLAINS WITH THE TROUGHING /INITIALLY...
500 MB HEIGHTS ABOUT 2.5 STD DEV BELOW CLIMO/. THE SOUTHERN PLAINS
AND EAST/SOUTHEAST SHOULD SEE NEAR TO ABOVE AVERAGE TEMPERATURES
WITH EXPANDING RIDGING. PRECIPITATION SHOULD LINGER NEAR THE
FRONTAL BOUNDARY IN THE CENTRAL CONUS /NEAR MISSOURI... ET AL./
BEFORE SHIFTING NORTHWARD AS WELL AS WESTWARD INTO MONTANA AS THE
NEXT TROUGH DIGS INTO THE PAC NW.


FRACASSO

$$





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