Prognostic Meteorological Discussion
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000
FXUS02 KWBC 311454
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1054 AM EDT FRI JUL 31 2015

VALID 12Z MON AUG 03 2015 - 12Z FRI AUG 07 2015

THE MEDIUM RANGE WEATHER PATTERN CONTINUES TO EVOLVE TOWARD A
TROUGH IN THE NORTHWEST AS COOL CONDITIONS RETURN...A RESET OF THE
MEAN RIDGE FROM THE SOUTHWEST NORTHWARD TOWARD THE ROCKIES/PLAINS
BY THE END OF THE PERIOD...AND THE DOMINANCE OF A TROUGH IN THE
EAST/NORTHEAST AS A MEAN UPPER LOW WORKS ITS WAY EASTWARD FROM
HUDSON BAY ACROSS SOUTHEAST CANADA. THE MOST SIGNIFICANT WEATHER
FEATURES WILL BE A COLD FRONT MAKING ITS WAY SOUTH AND EAST ACROSS
THE NORTHWEST...WARM TO HOT WEATHER EXTENDING FROM THE SOUTHWEST
ACROSS THE ROCKIES/PLAINS INTO THE SOUTHEAST...AND A SIGNIFICANT
COLD/STATIONARY FRONTAL BOUNDARY EXTENDING FROM THE NORTHERN
PLAINS/MID MISSISSIPPI VALLEY/OHIO VALLEY AND ACROSS THE EAST.
THIS BOUNDARY WILL LIKELY BE THE FOCUS FOR PRECIPITATION EITHER
AHEAD OF THE COLD FRONT OR ALONG THE STATIONARY FRONT AS POSSIBLE
SHORTWAVE SYSTEMS INITIATE THE POTENTIAL FOR SIGNIFICANT RAINFALL.

IN GENERAL...THERE WAS ABOVE AVERAGE AGREEMENT NOT ONLY BETWEEN
THE ENSEMBLE MEANS BUT WITH THE 06Z GFS AND 00Z ECMWF AS WELL.
WITH THE MEANS...THE GEFS MEAN REMAINED SLIGHTLY FASTER THAN THE
EUROPEAN/NAEFS MEAN WITH THE MOVEMENT OF THE CLOSED LOW ACROSS
SOUTHEAST CANADA...BUT THE EUROPEAN/NAEFS SOLUTION WAS CHOSEN TO
FORM THE ENSEMBLE MEAN COMPONENT OF THE FORECAST BLEND...RATHER
THAN THE GEFS MEAN. THESE DIFFERENCES ARE CONSIDERED ONLY
MINOR...ESPECIALLY FOR A MEDIUM RANGE FORECAST. PERHAPS THE
LARGEST DIFFERENCES OCCURRED WITH THE NORTHWESTERN TROUGH WITH THE
GEFS/NAEFS MEANS TRENDING FASTER THAN THE EUROPEAN MEANS IN
BRINGING IT EASTWARD ACROSS THE NORTHWEST.  THEREFORE...THERE IS
SLIGHTLY MORE UNCERTAINTY WITH THE SPEED OF THE FRONT CROSSING THE
NORTHWEST BUT ONLY ON  DAYS 6 AND 7/THURSDAY AND FRIDAY.

IN ADDITION...THE MOST RECENT RUNS OF THE 00Z ECMWF AND 06Z GFS
APPEARED RELATIVELY SIMILAR TO EACH OTHER AND NOT A BAD MATCH FOR
WHAT THE ENSEMBLE MEANS SHOWED...POSSIBLY PROVIDING SOME DETAIL
ESPECIALLY WITH SHORTWAVE ENERGY CROSSING THE WESTERN RIDGE AND
INTERACTING WITH THE EASTERN TROUGH.  THE MEANS DO NOT SHOW ANY
HINT OF THESE FEATURES AS EXPECTED.  THIS IS ESPECIALLY TRUE FOR A
POSSIBLE SYSTEM THAT CUTS ACROSS THE MISSISSIPPI VALLEY ON
WEDNESDAY/DAY 5 AND NEARS THE EAST COAST ON THURSDAY/DAY 6.
FEATURES SUCH AS THESE HAVE THE POTENTIAL TO ACTIVATE CONVECTIVE
DEVELOPMENT NEAR THE SURFACE FRONTS ACROSS THESE AREAS. SUCH
SHORTWAVE FEATURES COULD ALSO SLOW THE SOUTHWARD PUSH OF COOLER
AIR ACROSS THE EAST...AND THE MODELS THE SOUTHWARD PUSH OF COOLER
AIR MAKING IT ACROSS THE MIDDLE ATLANTIC STATES BY DAY
7/FRIDAY...BUT THIS IS ALSO WHEN THE FORECASTS HAVE THE LEAST
CONFIDENCE A WEEK OUT.

KOCIN

$$




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