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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1546Z Nov 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
1046 AM EST MON NOV 17 2014

VALID 12Z THU NOV 20 2014 - 12Z MON NOV 24 2014

...CENTRAL TO EASTERN US COLD SNAP TO GRADUALLY MODIFY LATE THIS
COMING WEEKEND...

...GUIDANCE/UNCERTAINTY ASSESSMENTS...

HAVE ELECTED TO GO WITH A MULTI MODEL BLEND SLIGHTLY FAVORING THE
00Z ECMWF/ECMWF ENSEMBLE MEAN BUT STILL INCLUDING A HEALTHY
PORTION OF 00Z GFS/06Z NAEFS ENSEMBLE MEANS.  THE OPERATIONAL VS
ENSEMBLE MEAN COMPONENT OF THE BLEND STARTS AT 70/30 ON DAY 3 AND
STAYS WITHIN EITHER A 70/30 OR 60/40 MAKEUP THROUGH DAY 5/SATURDAY
AND THEN DROPS TO A 50/50 MIX ON SUNDAY AND A 60/40 BLEND FAVORING
THE MEANS ON DAY 7/MONDAY.

IN GENERAL...THE OPERATIONAL 00Z ECMWF AND THE 00Z GFS...MORE SO
THAN THE 06Z GFS...REPRESENTED REASONABLE REPRESENTATIONS OF
MEDIUM RANGE PROBABILITIES THROUGHOUT WITH THE POSSIBLE EXCEPTION
OF ALONG THE PACIFIC NORTHWEST LATER IN THE FORECAST...WHERE LARGE
GFS DIFFERENCES FROM THE MEANS MAY HAVE FAVORED THE ECMWF. 
FARTHER EAST...WHILE THERE ARE SOME CONSIDERABLE DIFFERENCES
BETWEEN THE 00Z ECMWF VS THE 00Z GFS...I LIKED THE IDEA THAT BOTH
MODELS SEEMED TO CONVERGE ON A SOLUTION OF A RATHER DEEP CYCLONE
OVER THE UPPER MIDWEST NEAR THE SAME LOCATION ON DAY
7/MONDAY...AND THAT THEY WERE BOTH REASONABLE SOLUTIONS GIVEN THE
SPREAD AND SHAPES SHOWN BY THEIR CORRESPONDING ENSEMBLE MEANS. 
THE OVERALL TREND OF THE FORECAST WITH THE FINAL COLD HIGH
PRESSURE SYSTEM MOVING FROM SOUTH CENTRAL CANADA ON DAY 3 TO THE
EAST COAST BY DAY 5/THURSDAY THRU SATURDAY...FOLLOWED BY A
SIGNIFICANT WARM UP WITH A DEVELOPING COMPLEX CYCLONE OVER THE
CENTRAL US BY DAY 6/SUNDAY CONSOLIDATING INTO A LARGE CYCLONIC
CIRCULATION NEAR THE UPPER MIDWEST BY MONDAY/DAY 7.  

...PATTERN AND SENSIBLE WEATHER HIGHLIGHTS...

THE MEDIUM RANGE FORECAST REPRESENTS A WHOLESALE CHANGE TO THE
SUCCESSION OF COLD AIR MASSES THAT HAS BEEN RECENTLY INVADING
LARGE AREAS OF THE NATION.  WHILE ONE FINAL COLD SHOT AND ITS
ASSOCIATED BUILDING HIGH PRESSURE AREA WILL MOVE FROM SOUTHERN
CANADA ACROSS THE MIDWEST TO THE EAST COAST FROM THURSDAY TO
SATURDAY...RETURN FLOW OFF THE GULF OF MEXICO WILL STREAM
NORTHWARD...INCREASING THE CHANCES FOR MOSTLY RAIN AND MILDER
TEMPERATURES FROM THE SOUTHERN PLAINS NORTH AND NORTHEASTWARD
ACROSS THE MISSISSIPPI VALLEY/SOUTHEAST AND EASTERN HALF OF THE
COUNTRY BY LATER SUNDAY INTO MONDAY.

AS THIS STREAM OF MOISTURE/WARMTH HEADS NORTH ON THE WEEKEND...IT
WILL BE FOLLOWED BY MORE OF A PACIFIC AIRMASS THAN AN ARCTIC
AIRMASS IN ITS WAKE WITH ONLY COOL CONDITIONS RETURNING TO THE
PLAINS STATES...AS OPPOSED TO THE ARCTIC CHILL THAT DOMINATED THE
LAST SEVERAL DAYS.  AS THE MEAN UPPER TROUGH BUILDS TOWARD THE
CENTRAL US OVER THE WEEKEND INTO EARLY NEXT WEEK...UPPER HEIGHTS
WILL BUILD NORTHWARD OVER THE WEST COAST WITH COOLER AIR MOVING
SOUTHEASTWARD ACROSS MUCH OF THE WEST.  IN GENERAL...THE PASSAGE
OF SEVERAL PACIFIC FRONTS WILL SPELL POSSIBLE HEAVY RAINS
ESPECIALLY ACROSS THE NORTHWEST QUARTER OF THE NATION...AND MORE
SPECIFICALLY FOR THE PACIFIC NORTHWEST AND CASCADES.

KOCIN