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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0631Z Apr 22, 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
231 AM EDT TUE APR 22 2014

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

...OVERVIEW AND GUIDANCE PREFERENCES...

THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A
COMPOSITE BLEND OF THE GFS/GFS ENSEMBLE MEAN AND ECMWF/ECMWF
ENSEMBLE MEAN ALONG WITH CONTINUITY DAYS 3-4/FRI-SAT IN A PERIOD
WITH SLIGHTLY LOWER THAN NORMAL FORECAST SPREAD/UNCERTAINTY. 
PREFER A MORE ENSEMBLE MEAN BASED FORECAST APPROACH DAYS 5-7 NEXT
SUN-TUE IN LUE OF EMBRACING ANY PARTICULAR DETERMINISTIC MODEL IN
A PERIOD WITH STEADILY GROWING FORECAST SPREAD/UNCERTAINTY.  THIS
WPC SOLUTION OVERALL LEANS SLIGHTLY MORE IN THE DIRECTION OF
AMPLITUDE OVER TIME FOLLOWING ENSEMBLE MEAN TRENDS AND FAVORABLE
PACIFIC AND NORTH AMERICAN WATER VAPOR IMAGERY LOOP SUPPORT.

AS SUCH...THE OVERALL PATTERN IS EXPECTED TO TRANSITION FROM
MODERATE PROGRESSION TOWARD A BLOCKIER/SLOWER MOVING REGIME BY THE
WEEKEND OR EARLY NEXT WEEK WITH HINTS OF A REX BLOCK PSBLY
DEVELOPING OVER CNTRL NOAM AND A MEAN TROUGH LINGERING OVER ERN
CANADA AND NERN CONUS.  WITHIN THIS EVOLUTION THE TWO GREATEST
UNCERTAINTIES APPEAR IN THE DAYS 5-7 SUN-TUE TIME FRAME...
IF/WHERE AN UPR LOW CLOSES OFF WITHIN THE WRN-CNTRL CONUS TROUGH
AND THE AMPLITUDE OF NERN CONUS TROUGHING/LATITUDE OF THE ASSOC
SFC FRONTAL BNDRY.  IN BOTH CASES THERE IS SIGNIFICANT SPREAD AND
IN SOME GUIDANCE VARIABILITY BETWEEN 12Z/00Z CYCLES. 


...SENSIBLE WEATHER HIGHLIGHTS...

SYSTEM INITIALLY OVER THE GREAT LAKES FRI WILL SPREAD PCPN ACROSS
THE ERN THIRD OF THE NATION WITH BEST ORGANIZED ACTIVITY LIKELY
NEAR THE SFC LOW TRACKING NEAR THE CANADIAN BORDER AND ALONG/AHEAD
THE TRAILING FRONT AND TO A LESSER EXTENT SECONDARY FRONTAL
PASSAGE.  RNFL IS FCST TO TREND LIGHTER AS THE FRONT CONTINUES
EWD.. THOUGH SOME ACTIVITY MAY DEVELOP ALONG THE TRAILING PART OF
THE FRONT AS IT STALLS OVER S-CNTRL PARTS OF THE CNTRL-ERN STATES.
 DEPENDING ON EXACTLY HOW THE SFC/UPR SYSTEM DEVELOPS THERE IS
POTENTIAL FOR SOME WINTRY PCPN CLOSER TO THE CANADIAN BORDER.

EXPECT MSTR TO MOVE INTO THE NWRN STATES THU/FRI WITH AN
INCREASINGLY BROAD SHIELD OF PCPN SPREADING ACROSS THE WEST IN
ASSOC WITH THE TROUGH ALOFT CROSSING THE REGION.  SOME LOCALLY
MDT-HVY PCPN IS PSBL OVER FAVORED NRN-CNTRL TERRAIN INCLUDING
ELEVATION SNOWS.  AS HEIGHT FALLS REACH THE PLAINS AND SPAWNS
CYCLO/FRONTO GENESIS EXPECT INCREASED POTENTIAL FOR SOME HEAVIER
RNFL OVER PORTIONS OF THE PLAINS THIS WEEKEND.  ACTIVITY/THREAT
SHOULD SPREAD ACROSS THE E-CENTRAL US EARLY NEXT WEEK IN A PERIOD
WITH IMPROVING RETURN MOISTURE FLOW INTO A WELL ORGANIZED WEATHER
SYSTEM.

SCHICHTEL