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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1541Z Jul 22, 2014)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1141 AM EDT TUE JUL 22 2014

VALID 12Z FRI JUL 25 2014 - 12Z TUE JUL 29 2014

...OVERVIEW AND MODEL PREFERENCES...

THERE IS STILL ABOVE AVERAGE CONFIDENCE IN A DISTINCT TREND TOWARD
AN AMPLIFICATION OF THE LONG WAVE PATTERN TOWARD A RIDGE IN THE
WEST AND A TROUGH IN THE EAST.  WHILE THERE ARE DISTINCT
DIFFERENCES BETWEEN MODELS IN THE EVOLUTION OF LOW PRESSURE
SYSTEMS/FRONTS...THE ENDING POINT OF THEIR EVOLUTION SEEMS MORE
CERTAIN THAN HOW THEY EVOLVED TO GET THERE.  IN OTHER WORDS...A
RELATIVELY PREDICTABLE WEATHER PATTERN IS UNDERWAY.

AT THE START OF THE FORECAST PERIOD/DAY 3/WEDNESDAY...THERE IS
LITTLE IN THE ACTUAL PATTERN THAT READILY SUGGESTS SUCH A CHANGE
IS UNDERWAY.  A RELATIVELY COOL MIDSUMMER AIRMASS IS ALREADY IN
PLACE ACROSS THE NORTHEAST SECTOR OF THE COUNTRY WITH TYPICAL
SUMMER HEAT ACROSS THE MIDDLE OF THE COUNTRY. A CYCLONE OVER
ALBERTA WITH A FRONT MOVING ACROSS THE NORTHWEST SIGNIFIES A
SHORTWAVE TROUGH CUTTING EASTWARD TO THE NORTH OF A BROAD UPPER
RIDGE OVER THE SOUTH CENTRAL US.

BY DAY 4/THURSDAY...THE PATTERN CHANGE JUST BEGINS TO EMERGE AS
THE SHORTWAVE TROUGH OVER SW CANADA DRIFTS EAST/SOUTHEASTWARD WITH
A RELATIVELY STRONG ZONAL BUT SLIGHTLY NORTHWESTERLY UPPER LEVEL
FLOW EXTENDS FROM THE PACIFIC NORTHWEST TOWARD THE EAST COAST. THE
06Z GFS WAS DISCOUNTED/MINIMIZED AT THIS POINT SINCE IT APPEARED
TO BE FAST WITH RESPECT TO THE ENSEMBLE MEANS AND THE 00Z GFS RUN
WITH THE MOVEMENT OF THE SW CANADIAN TROUGH.  BY DAY
5/FRIDAY...THE PATTERN CHANGE IS CLEAR AS THE SHORTWAVE TROUGH
BEGINS TO MOVE ON A MORE SOUTHEASTERLY DIRECTION ACROSS THE
NORTHERN MISSISSIPPI VALLEY WHILE THE SOUTHERN PLAINS RIDGE SHIFTS
WESTWARD AS HEIGHTS RISE ACROSS THE NORTHWEST US. 

THE EVOLUTION TOWARD AN AMPLIFIED RIDGE IN THE WEST AND A
DEEPENING TROUGH IN THE EAST IS QUITE STRIKING ON DAYS 6 TO 7/THIS
COMING WEEKEND. WHILE THERE IS UNCERTAINTY WITH THE LOCATIONS OF
FRONTS AND LOW PRESSURE SYSTEMS ON DAYS 4 TO 5 IN
PARTICULAR...WITH MULTIPLE POSSIBLE AREAS OF WEAK LOW PRESSURE AND
A VARIETY OF TROUGHS/FRONTS ACROSS THE NORTHERN HALF OF THE US. 
THESE AMORPHOUS SYSTEMS APPEAR TO BECOME MORE DISTINCT WITH LOW
PRESSURE DEVELOPING OVER THE MIDWEST ON DAY 6/SATURDAY WITH AN
EASILY DEFINABLE COLD FRONT MOVING SOUTH AND EASTWARD ACROSS MUCH
OF THE EAST EXCEPT FOR THE GULF COAST/FLORIDA ON DAY 7/SUNDAY.

THE OVERNIGHT ENSEMBLE MEANS ARE QUITE CONSISTENT WITH EACH OTHER
AS WELL AS WITH THE 00Z ECMWF AND 00Z GFS THROUGH DAY 7.  AS
MENTIONED...THE 06Z GFS WAS DISCARDED.  GIVEN THE HIGH LEVEL OF
AGREEMENT...MUCH OF THE BLEND USED FOR THE FORECAST GAVE PRIORITY
TO THE OPERATIONAL RUNS...ESPECIALLY SINCE THE DETAIL IN THE
OPERATIONAL FORECAST WAS MORE EASILY RESOLVED ON DAYS 6 AND 7. 
THE 00Z ECMWF WAS GIVEN MORE WEIGHT THROUGHOUT THE FORECAST THAN
THE GFS.


KOCIN