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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1554Z Aug 25, 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
1154 AM EDT MON AUG 25 2014

VALID 12Z THU AUG 28 2014 - 12Z MON SEP 01 2014

...OVERVIEW...
PROGRESSIVE FLOW PREVAILS ACROSS THE NORTH AMERICAN CONTINENT THIS
MEDIUM RANGE PATTERN...BASED UPON THE SIGNAL FOR PERSISTENT OF
DEEP TROUGHING IN THE BERING SEA/GULF OF ALASKA AND PROJECTED
250MB JET AXIS STREAKING ACROSS THE PACIFIC NORTHWEST LATE IN THE
FORECAST PERIOD.  

...MODEL PREFERENCES/GUIDANCE ASSESSMENT...
25/00Z MODELS AND ENSEMBLES WERE IN MUCH BETTER AGREEMENT OVER
CANADA AND THE PROGRESSIVE NATURE OF THE FLOW PATTERN ACROSS THE
GULF OF ALASKA AND DOWNSTREAM INTO THE LOWER 48 THIS MEDIUM RANGE
PERIOD. DAY 3 BEGINS WITH A FRONTAL PASSAGE LINING UP ALONG THE
EAST COAST...AND FOLLOWED BY A PAIR OF WELL-DEFINED UPPER-LEVEL
SYSTEMS TRACKING FROM WEST TO EAST ACROSS THE CONTINENT.

THE 25/00Z DETERMINISTIC GFS LOOKED A TAD BIT FASTER WITH THE
MID-LEVEL FLOW ON DAY 5-6 ACROSS THE GREAT BASIN AND DOWNSTREAM
OVER KANSAS AND MISSOURI--ALONG I-70 CORRIDOR. THIS SOLUTION TAKES
ON MORE TROPICAL MOISTURE AND MID-LEVEL INSTABILITY FROM A REMNANT
'MARIE' THAN OTHER SOLUTIONS. HOWEVER...IT HAS CARRIED THIS
SOLUTION FOR THE BETTER PART OF A WEEK AND CANNOT BE TOTALLY RULED
OUT. THE 25/00Z DETERMINISTIC ECMWF IS THE SLOWEST
SOLUTION...FOCUSING MORE ON THE ENERGY ASSOCIATED WITH THE 250MB
JET NOSING INTO THE NORTH CENTRAL ROCKIES FROM THE WEST. THE
25/00Z DETERMINISTIC CANADIAN/UKMET BLENDING MORE GULF MOISTURE
INTO THE MIX ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE.
 

THOUGHT THE 60/20/20 WEIGHTING PREFERRED BY THE MIDSHIFT--WAS
EASILY PRESERVED BY A SIMILAR RATIO OF THE 25/12Z ECMWF-NAEFS-GEFS
MEANS BEYOND DAY 5. THIS MAINTAINS VERY CONTINUITY WITH THE
PATTERN ALOFT AND ITS SEQUENCE OF BROAD-SCALE MIGRATORY
MID-LATITUDE WAVES--FROM WEST TO EAST. HOPING THE FINER DETAILS OF
THE DETERMINISTIC RUNS--GIVEN ANOTHER CYCLE OR 2--WILL GRASP THE
SCOPE OF THE MOISTURE PROFILES AND COME INTO BETTER AGREEMENT FROM
CALIFORNIA EASTWARD INTO THE SOUTHERN PLAINS.

...SENSIBLE WEATHER HIGHLIGHTS...
THE EXITING EAST COAST COLD FRONT ON DAY 3 WILL BRIEFLY
RECONFIGURE THE SUBTROPICAL RIDGE AXIS OVER THE
SOUTHEAST...ALLOWING FOR A LESS HUMID AIRMASS TO MOVE INTO THE
SOUTHEASTERN STATES. THE PAIR OF PACIFIC FRONTS MIGRATING ACROSS
THE CONTINENT WILL FURTHER DAMPEN THE RIDGE...NOT DESTROY IT...BUT
FORCE ITS MID-LEVEL AXIS TO WEAKEN IN THE WESTERN PORTION OF THE
GULF OF MEXICO AND MISS DELTA REGION THIS FORECAST PERIOD.

HIGHEST PROBABILITIES OF PRECIPITATION WILL FOLLOW THE PACIFIC
SHORTWAVE THROUGH THE CENTRAL PLAINS AND UPPER GREAT LAKES DAYS
3-5--AND THE NEXT PACIFIC TROUGH MOVING INTO WEST CENTRAL COAST OF
CANADA AND NORTHWEST STATES...AFTER DAY 5.

THERE REMAINS A SMALL WINDOW OF OPPORTUNITY FOR REMNANT
UPPER-LEVEL TROPICAL MOISTURE FROM 'MARIE' TO BECOME ENTRAINED IN
THE WESTERLIES--ALONG THE CALIFORNIA COAST--AROUND DAY 5 AND DAY
6. 

VOJTESAK