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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1528Z Aug 19, 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
1128 AM EDT TUE AUG 19 2014

VALID 12Z FRI AUG 22 2014 - 12Z TUE AUG 26 2014

THE MEDIUM RANGE FEATURES AN UPPER RIDGE POPPING NORTHWARD ACROSS
THE EAST CENTRAL US WHILE A WEAK UPPER TROUGH MOVES VERY SLOWLY
EASTWARD ACROSS THE NORTHEAST CORNER OF THE COUNTRY. 
MEANWHILE...A SIGNIFICANT UPPER LEVEL TROUGH IS EXPANDING ACROSS
THE WESTERN US...WHILE A PORTION LIFTS NORTHEASTWARD INTO SOUTHERN
CANADA WHILE HEIGHTS REMAIN RELATIVELY LOW OVER THE NORTHERN TIER
OF THE COUNTRY BY THE END OF THE FORECAST...WITH THE UPPER RIDGE
MOVES SLOWLY EASTWARD TOWARD THE EAST COAST.

MOST OF THE MODEL DIFFERENCES PERTAIN TO HOW THE TROUGH OUT WEST
EVOLVES...ESPECIALLY WITH ANY PORTION THAT LIFTS NORTHEASTWARD
INTO SOUTHERN CANADA BY DAY 5.  THERE APPEARS TO BE QUITE A RANGE
OF SOLUTION WITH RESPECT TO THE SPEED AT WHICH THIS OCCURS WITH
THE 00Z ECMWF SLOWEST...THE 00Z AND 06Z GFS SOMEWHAT FASTER AND
THE 00Z CANADIAN BY FAR THE FASTEST.  THE DIFFERENCE IN THE
ECMWF/GFS IS ALSO REFLECTED IN THE MEANS SO A COMPROMISE BETWEEN
THE TWO MODELS WAS SOUGHT WHILE EFFECTIVELY IGNORING THE 00Z
CANADIAN AS TOO FAST AS WELL AS THE UKMET WHICH HAS A STRONGER
SHORTWAVE LIFTING INTO SOUTHERN CANADA ON DAY 5. IN GENERAL...THE
EASTWARD MOVEMENT OF THE FRONT LATER IN THE FORECAST CROSSING THE
MIDWEST TOWARD THE EAST HAS SLOWED FROM THE OVERNIGHT FORECAST.

THE SENSIBLE WEATHER DURING THE FORECAST INCLUDES VERY WARM
CONDITIONS UNDER THE UPPER RIDGE FROM SOUTHERN PLAINS AND
MISSISSIPPI VALLEY INTO THE MIDWEST/OHIO VALLEY EARLY IN THE
FORECAST.  A BACKDOOR COLD FRONT IS ASSOCIATED WITH THE WEAK
TROUGH ALONG THE EAST COAST THAT APPEARS TO TRAVEL SOUTHWARD ALONG
MUCH OF THE EAST COAST INCLUDING GEORGIA AND SOUTH CAROLINA BY DAY
5. HIGH PRESSURE AND EASTERLY FLOW WILL DOMINATE THE COAST THROUGH
THIS PERIOD.  MUCH COOLER CONDITIONS WILL EXPAND SOUTH AND
EASTWARD FROM THE NORTHWEST ACROSS THE NORTHERN ROCKIES AND PLAINS
BY DAY 5.

A COMPLEX AREA OF LOW PRESSURE WITH POSSIBLE SEVERAL LOW PRESSURE
CENTERS/FRONTAL BOUNDARIES WILL SEPARATE THE TROUGH OVER THE
NORTHWEST FROM THE RIDGE ACROSS THE EAST CENTRAL STATES ESPECIALLY
ON DAYS 3 TO 4.  RAINFALL/THUNDERSTORMS WILL BE FOCUSED NEAR THESE
BOUNDARIES WITH THE THREAT OF SOME HEAVY/SEVERE THUNDERSTORMS IN
THE WARMER AIR WITH RAIN AND COOL CONDITIONS WITH THE WESTERN
TROUGH.  THERE IS EVEN THE CHANCE FOR SOME HIGH ELEVATION SNOW IN
THE CENTRAL TO NORTHERN ROCKIES.

LATE IN THE FORECAST...COOLER AIR IS STILL DIFFICULT TO DISLODGE
ALONG THE EAST COAST AS THE WEDGE OF WARMER AIR GETS SQUEEZED
BETWEEN THE EASTERN SURFACE HIGH AND THE APPROACHING FRONT FROM
THE WEST.  BY DAY 7...COOLER AIR HAS MADE ITS WAY EASTWARD FROM
THE NORTHERN PLAINS ACROSS THE MIDWEST...BUT THE EASTWARD DRIFT
APPEARS TO BE SLOWER THAN EARLIER FORECASTS AS COOLER AIR MAY
AGAIN MAKE INROADS ACROSS THE NORTHWEST.

KOCIN