Prognostic Meteorological Discussion
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FXUS02 KWBC 020458
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1258 AM EDT SUN AUG 02 2015

VALID 12Z WED AUG 05 2015 - 12Z SUN AUG 09 2015

AN UPPER-LEVEL TROUGH CENTERED NEAR JAMES BAY WILL PRODUCE A
COOLER WEATHER PATTERN FOR THE NORTHEAST QUARTER OF THE `LOWER
48`. BY THE END OF THE FORECAST PERIOD---A GRADUAL WEST-TO-EAST
PROGRESSION OF A MIGRATORY TROUGH-RIDGE COUPLET ALONG THE WEST
CENTRAL COAST OF NORTH AMERICA WILL TRY TO DISLODGE THE TROUGH
ATTEMPTING TO ANCHOR OVER EASTERN CANADA.

AFTER DAY 4---MODEL CONTENTION EMERGES ACROSS SOUTH CENTRAL CANADA
AND THE TRANSFER OF PACIFIC ENERGY INTO THE DOWNSTREAM TROUGH
ANCHORED OVER SOUTHEAST CANADA. THE 1/12Z & 1/18Z DETERMINISTIC
GFS HAVE BROKEN RANKS WITH THE LONG WAVE RIDGE SOLUTION---AND
CRASH A STRONG SHORTWAVE THROUGH THE HEART OF THE RIDGE
AXIS...ALLOWING TO MIGRATE SOUTHEASTWARD INTO THE BASE OF THE
500MB TROUGH. THIS SHORTWAVE IS `TRACK-ABLE`---ORIGINATING EAST OF
EDMONTON ALBERTA AROUND 5/18Z  AND REACHING SAULT SAINTE-MARIE
MICHIGAN BY 8/00Z. THESE 2 SOLUTIONS WERE NOT INCLUDED IN THE
BLEND. THE DETERMINISTIC 1/12Z ECMWF AND CANADIAN...ALONG WITH THE
PREVIOUS WPC FORECAST (AND ITS INCORPORATION OF THE 1/00Z GFS)
WERE THE 3 BEST CHOICES. ALL THREE MAINTAINED GOOD CONTINUITY WITH
RESPECT TO --- WHAT HAS BEEN THE GENERALLY ACCEPTED 500MB WAVE
PATTERN AND WPC FORECAST FOR 2-3 DAYS NOW ACROSS NORTH AMERICA.

FOR DAYS 4-7 WILL TAILOR THE NATIONAL FORECAST WITH THE 1/12Z
ECENS/NAEFS MEAN AND CONSIDER USING SOME OF THE 3 AFOREMENTIONED
DETERMINISTIC SOLUTIONS UNTIL DAY 6. THIS IMPLIES USING THE
PREVIOUS WPC FORECAST (ABOUT 30% OF THE BLEND) FOR
TEMPS/POPS...SURFACE/500MB GRAPHICS INTO DAY 6 AND SHOULD KEEP A
DAY 4 CANADIAN FRONT MIGRATING ACROSS THE CENTRAL APPALACHIANS AND
OUT TO SEA ALONG THE DELMARVA/OUTER BANKS CORRIDOR AROUND DAY 5.
THE KEY BEING---THIS ALLOWS THE CANADIAN SURFACE HIGH TO BUILD IN
BEHIND THE FRONT AND SPREAD THE DRIER...COOLER AIRMASS INTO THE
NORTHEAST QUARTER OF THE NATION.

THE CHALLENGE FOR THE EASTERN HALF OF THE NATION CONTINUES TO BE
THE OUTCOME OF THE EASTERN NORTH AMERICAN TROUGH`S AMPLITUDE. FOR
IT WILL BE ALONG ITS BASE---THAT THE BEST PROSPECTS FOR
SIGNIFICANT RAINFALL WILL LIKELY OCCUR. AND A SECONDARY ASPECT OF
THE TROUGH`S AMPLITUDE --- WILL BE THE DURATION AND TRAJECTORY OF
COOL CANADIAN SURFACE HIGH PRESSURE --- SPREADING ACROSS THE
NORTHERN PLAINS...THE GREAT LAKES AND NEW ENGLAND.

VOJTESAK

$$




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