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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0615Z Aug 17, 2014)
 
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Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
215 AM EDT SUN AUG 17 2014

VALID 12Z WED AUG 20 2014 - 12Z SUN AUG 24 2014

.OVERVIEW...
FLOW PATTERN ALOFT REMAINS CONSISTENT ACROSS NORTH AMERICA WITH
ENERGETIC NORTH PACIFIC JET STREAM INFLUENCES TEMPORARILY ALTERING
THE WEATHER PATTERN ACROSS THE LOWER 48 FROM WEST TO EAST.
BLOCKINESS OVER ATLANTIC CANADA AND GREENLAND ALLOW FOR THE
'BERMUDA HIGH' AND SOUTHEAST RIDGE TO BUILD WESTWARD INTO THE
SOUTHEAST QUARTER OF THE NATION...PRIMARILY SOUTH OF THE TENNESSEE
RIVER AND EAST OF THE MISSISSIPPI---AND A SPLIT-FLOW PATTERN TO
DEVELOP EAST AND NORTH OF THE MISSOURI VALLEY. 

.MODEL PREFERENCES/UNCERTAINTY ASSESSMENT...
COULD NOT FIND MUCH FAULT WITH THE 16/12Z ECENS MEAN AND NAEFS
MEAN THIS MEDIUM RANGE FORECAST PERIOD. THE 16/12Z ECENS...GEFS
AND NAEFS MEANS GENERALLY AGREE THAT A FLATTER NORTHERN STREAM
JET-LEVEL FLOW REMAINS ALONG THE US/CANADIAN BORDER WITH
SIGNIFICANT HEIGHT FALLS OVER THE NORTHERN ROCKIES DRAWING COOLER
CANADIAN AIR--EAST OF THE DIVIDE...RATHER THAN WEST OF THE DIVIDE.
WPC CONTINUITY AND THIS MID SHIFT SURFACE/500MB D3-7 GRAPHIC AGREE
WITH THE CONSENSUS. 

THE 16/12Z DETERMINISTIC GUIDANCE CONTINUES TO FLIP-FLOP THE
SOLUTION ALONG THE CALIFORNIA COAST AFTER DAY 4 WITH MID-LEVEL
ENERGY EJECTING FROM THE 300MB-500MB LAYERED CUTOFF MEANDERING OFF
THE SOUTH CENTRAL CALIFORNIA COAST. THIS 16/12Z CYCLE...IT WAS THE
ECMWF'S TURN TO DIG THE CUTOFF INTO THE DESERT SOUTHWEST AND FOUR
CORNERS AREA...FOLLOWING IN THE FOOTSTEPS OF THE GFS AND CANADIAN
ON EACH OF THE LAST TWO MID SHIFTS.

THE 'FLIP-FLOPPING' ESSENTIALLY REVOLVES AROUND THE 'PHASING' OF
ENERGY WITH INDIVIDUAL SOLUTIONS THAT ARE WILLING TO GENERATE/WORK
A SURGE OF NORTH TO NORTHWEST NORTHERN STREAM FLOW--IN BEHIND THE
LONG WAVE TROUGH MIGRATING THROUGH THE PACIFIC NORTHWEST AND
WESTERN CANADA. IN SOME RUNS...THE PHASING GETS EXTREME...EVEN
ALLOWING TROPICAL ENERGY/MOISTURE FROM 'KARINA' TO BECOME
ENTRAINED IN THE MID-LATITUDE FLOW PATTERN. THESE ARE VERY-LOW
PROBABILITY SOLUTIONS...BUT INDIVIDUAL DETERMINISTIC RUNS CONTINUE
TO GO THIS ROUTE FROM CYCLE TO CYCLE.

OF NOTE...THE PREFERRED 16/12Z ECENS/NAEFS ENSEMBLE BLEND DOES NOT
DISMISS THE WEST COAST CUTOFF'S MIGRATION SOUTH-SOUTHWESTWARD
ALONG 125W. RATHER--IT ACKNOWLEDGES ITS PRESENCE AS A 582DM CLOSED
LOW. TO ME...IT APPEARS TO BE A SHALLOW...PACIFIC TUTT-CELL LIKE
FEATURE IN THE FLOW PATTERN---AND TREATING IT AS SUCH...WOULD
IMPLY THE CIRCULATION WILL BE MORE OF AN ACTIVE NOCTURNAL WEATHER
PHENOMENA/SENSIBLE WEATHER 'GENERATOR'.   

...SENSIBLE WEATHER HIGHLIGHTS...
DAYS 3-7--POINTS EAST AND NORTH OF THE MISSISSIPPI AND OHIO
RIVERS...ALONG WITH THE NORTHERNMOST US ROCKIES WILL RECEIVE THE
HIGHEST PRECIPITATION.

EXPANSION OF THE UPPER-LEVEL RIDGE ACROSS THE SOUTHEAST WILL LOCK
IN THE HEAT AND HUMIDITY ACROSS THE REGION...WHILE A BACKDOOR COLD
FRONT RETURNS THE NORTHEAST COAST TO COOLER CONDITIONS DAY 6-7.

HIGH TEMPERATURES LOOK TO BE 15F-20F DEGREES BELOW NORMAL FOR DAYS
6-7 ACROSS THE NORTHERN ROCKIES AS THE PACIFIC FRONT ROLLS THROUGH
THE REGION.

VOJTESAK