Prognostic Meteorological Discussion
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4
000
FXUS02 KWBC 021525
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1124 AM EDT SUN AUG 02 2015

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

THE MEAN 500 MB PATTERN CONTINUES TO SHOW A TROUGH/RIDGE/TROUGH
STRETCHING FROM THE WEST COAST TO THE EAST COAST OF CANADA WITH A
WAVY WESTERLY FLOW STRETCHING ACROSS THE NORTHERN TIER OF THE US.
DURING THE FORECAST PERIOD...A SHORTWAVE SYSTEM EMBEDDED WITHIN
THE FLOW ACROSS THE CENTRAL US MOVES EASTWARD AND SERVES TO
AMPLIFY THE TROUGH IN THE EAST AS A SERIES OF LOW PRESSURE SYSTEMS
MIGRATE EASTWARD FROM THE CENTRAL TOWARD THE EASTERN US.
MEANWHILE...A COLD FRONT GRADUALLY SLIPS ALL THE WAY SOUTH AND
EASTWARD BY DAY 7/SUNDAY TO THE GULF STATES AND OFF THE EAST
COAST.  THIS APPEARS TO FAVOR A SIGNIFICANT LATE SUMMER SURGE OF
REFRESHINGLY DRIER AND EVEN COOLER AIR WILL COVER MUCH OF THE EAST
BY LATE IN THE FORECAST EVEN THOUGH THE FORECAST IS LESS RELIABLE
THIS FAR IN THE FUTURE BUT THE GENERAL MODEL SIGNALS SEEM CLEAR.
DISTURBANCES THAT WILL STILL BE DIFFICULT TO RESOLVE ASSOCIATED
WITH THE FRONTAL SYSTEMS WILL PRODUCE SHOWERS/THUNDERSHOWERS
ESPECIALLY PREVALENT ACROSS THE NORTHERN TO CENTRAL PLAINS...THE
MID UPPER MISSISSIPPI VALLEY AND ACROSS MUCH OF THE SOUTHERN
MIDWEST/OHIO VALLEY/MIDDLE ATLANTIC STATES WITH SHOWERS/STORMS
AHEAD OF THE COLD FRONT PUSHING INTO THE TENNESSEE VALLY AND
SOUTHEAST.

WHILE THE STABLE PATTERN OVER CANADA AND THE US HAS HELD FOR
SEVERAL DAYS...THERE A SEVERAL CHANGES THAT ARE BEGINNING TO OCCUR
IN THE LARGER SCALE PATTERN.  THE TROUGH OVER THE NORTHWEST
APPEARS TO MOVE INLAND ACROSS SOUTHWESTERN CANADA AND APPEARS TO
DAMP OUT BENEATH THE STRONG RIDGE OVER NORTH CENTRAL CANADA.
ANOTHER TROUGH ORIGINATING OVER THE GULF OF ALASKA EARLY IN THE
FORECAST WILL MIGRATE SOUTHEASTWARD AND APPROACH THE NORTHWEST
COAST LATER IN THE FORECAST.  THIS SYSTEM EFFECTIVELY KICKS OUT
THE RESIDENT TROUGH.  FINALLY...AN UPPER LOW FORECAST NEAR 30N
135W ON DAY 3/WEDNESDAY ABOUT 600 MILES WEST OF THE CALIFORNIA
COAST WILL MOVE EASTWARD NEARING AND CROSSING CALIFORNIA ON DAYS 5
AND 6/FRIDAY AND SATURDAY AND WILL INCREASE THE POTENTIAL FOR
CONVECTION IN PARTS OF CALIFORNIA AND THE INTERIOR WEST.

FROM A MODELING PERSPECTIVE...IT WAS STILL EASY TO THROW OUT THE
00Z CANADIAN EARLY IN THE PROCESS SINCE IT SEEMED TO HAVE TOO MANY
FEATURES THAT APPEARED AS OUTLIERS WITHIN THE ENSEMBLE SUITE OF
SOLUTIONS.  WHILE THE 06Z GFS APPEARED RELATIVELY SUFFICIENT...IT
ALSO HAD SOME OUTLIER SOLUTIONS OVER THE OHIO VALLEY ON DAYS 4
THROUGH 6/WEDNESDAY THROUGH SATURDAY...SUGGESTING THAT THE LOW
PRESSURE WOULD MOVE SLOWER AND FARTHER NORTH THAN THE MAJORITY OF
SOLUTIONS WITHIN THE ENSEMBLE CLUSTER.  THE 00Z GFS AND THE 00Z
ECMWF BOTH SEEMED TO BE MORE SIMILAR TO EACH OTHER AND HAD
SIGNIFICANT AGREEMENT WITH THE GEFS/NAEFS/EUROPEAN ENSEMBLE MEANS
THAT WARRANTED A USE OF AT LEAST A 50 PERCENT COMPONENT FOR THE
BLEND THROUGH DAY 7/SUNDAY!  WHILE THE DAY 3 FORECAST BASICALLY
CONSISTED OF A BLEND MOSTLY OF THE OPERATIONAL GFS/ECMWF...THE DAY
4 TO 7 FORECASTS ALL CONSISTED OF AN EVEN BLEND OF 50 PERCENT
OPERATIONAL AND 50 PERCENT ENSEMBLE MEANS WITH A VARYING BLEND OF
THE 00Z ECMWF/00Z GFS/00Z NAEFS AND 00Z EUROPEAN MEANS.

KOCIN


$$




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.