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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0647Z Nov 18, 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
147 AM EST TUE NOV 18 2014

VALID 12Z FRI NOV 21 2014 - 12Z TUE NOV 25 2014

...WARMING TREND IN STORE FOR THE EASTERN THIRD OF THE U.S. BY
LATE IN THE WEEKEND...

...PATTERN...

TO BEGIN THE MEDIUM RANGE PERIOD...A BROAD UPPER VORTEX WILL LIFT
AWAY FROM THE GREAT LAKES/NORTHEASTERN U.S. EARLY FRIDAY WITH THE
FLOW FLATTENING OUT IN ITS WAKE. SPLIT FLOW ACROSS THE WESTERN
U.S. WILL FEATURE A LOBE OF VORTICITY DIGGING INTO THE
SOUTHWESTERN U.S. ON FRIDAY MORNING. THIS SYSTEM IS EXPECTED TO
TRANSLATE EASTWARD REACHING THE SOUTHERN HIGH PLAINS BY EARLY IN
THE WEEKEND. WITH HEIGHTS BUILDING OVER THE EASTERN CONUS...THIS
LEAD IMPULSE IS FORECAST TO ATTAIN A NEGATIVE TILT WHILE LIFTING
THROUGH THE OZARKS AND EVENTUALLY INTO THE GREAT LAKES REGION BY
SUNDAY. MODELS SHOW ADDITIONAL SHORTWAVE ENERGY SPILLING INTO THE
SOUTHWESTERN U.S. LATER IN THE PERIOD AS BROAD MID-LEVEL RIDGING
SETS UP ALONG 13OW-140W LONGITUDE. BY EARLY NEXT WEEK A LONGWAVE
TROF IS EXPECTED TO ENCOMPASS A SIGNIFICANT PORTION OF THE COUNTRY
EXTENDING FROM THE INTERMOUNTAIN WEST ALL THE WAY TO THE OH/TN
VALLEYS.


...MODEL EVALUATION/WPC PREFERENCES...

ON DAY 3/FRIDAY...THE MODELS ARE GENERALLY IN SUFFICIENT AGREEMENT
WITH THE UPPER PATTERN WHILE TIMING DIFFERENCES EVENTUALLY GROW
WITH THE SOUTHERN STREAM EJECTING OUT OF THE DESERT SOUTHWEST. THE
18Z GFS/12Z CMC WERE THE QUICKEST TO SLIDE THE SHORTWAVE TOWARD
THE PLAINS WHILE ENSEMBLE MEANS AND A VAST MAJORITY OF THE MEMBERS
WITHIN THE SPAGHETTI PLOT SUGGEST SLOWER MIGHT BE MORE REASONABLE.
THE 12Z GFS/ECMWF/UKMET FAVORED THE SLOWER PROGRESSION WHICH WAS
THE PREFERENCE THROUGH DAY 4/SATURDAY. BY LATER IN THE
WEEKEND...THE 12Z UKMET BECOMES MUCH MORE AGGRESSIVE WITH THIS
LEAD IMPULSE ALONG WITH THE ADDITIONAL ENERGY DIGGING INTO THE
SOUTHERN HIGH PLAINS ON SUNDAY MORNING. PLAYED IT A LITTLE MORE
CONSERVATIVELY AND REMOVED THE 12Z UKMET BY DAY 5/SUNDAY AND
LEANED A BIT MORE ON THE 12Z GFS/ECMWF. FOR DAYS 6 AND
7...MONDAY/TUESDAY...HAD TO ABANDON THE DETERMINISTIC MODELS AS
THEY VARY IN HOW DEVELOPED THE CYCLONE BECOMES OVER THE GREAT
LAKES. THE PAST COUPLE CYCLES OF THE ECMWF...PARTICULARLY THE 12Z
RUN...FAVOR A RAPIDLY DEEPENING CYCLONE APPROACHING 970-MB. WHILE
THIS IS DEFINITELY WITHIN THE REALM OF POSSIBILITIES...FELT MORE
COMFORTABLE FOLLOWING THE MORE STABLE AND CONSERVATIVE 18Z
GEFS/12Z ECMWF ENSEMBLE MEANS THROUGH DAY 7/TUESDAY.


...SENSIBLE WEATHER HIGHLIGHTS...

IT WILL BE QUITE CHILLY TO BEGIN THE PERIOD WITH A STRONG SURFACE
RIDGE ANCHORING THE UPPER MIDWEST...GREAT LAKES...AND NORTHEASTERN
U.S. THIS WILL FAVOR READINGS ANYWHERE BETWEEN 10 AND 20 DEGREES
BELOW CLIMATOLOGY ON DAYS 3/4. AS THE UPPER VORTEX LIFTS FARTHER
INTO EASTERN CANADA AND THE SURFACE HIGH EXITS INTO THE WESTERN
ATLANTIC...RETURN FLOW AHEAD OF THE NEXT DEVELOPING CYCLONE WILL
GRADUALLY BRING TEMPERATURES CLOSER TO NORMAL. STRONG WARM
ADVECTION AHEAD OF THIS SYSTEM WILL RAISE FORECAST HIGHS TO 5 TO
10 DEGREES ABOVE NORMAL WHICH IS IN STARK CONTRAST TO THE AIR MASS
CURRENTLY IN PLACE OVER THIS REGION. THE STRONG BAROCLINIC ZONE
WILL ALSO BE THE SITE FOR HEAVY PRECIPITATION ANYWHERE FROM THE
GREAT PLAINS EASTWARD AS THE BOUNDARY PROGRESSES TOWARD THE EAST.
AN ADDITIONAL AREA OF UNSETTLED WEATHER WILL BE ACROSS THE PACIFIC
NORTHWEST WHERE A SERIES OF IMPULSES OFF THE PACIFIC ARE EXPECTED
TO ADVANCE INLAND THROUGHOUT THE PERIOD. THE COMBINATION OF
ENHANCED PACIFIC MOISTURE AND UPSLOPE FLOW WILL FOCUS MUCH OF THE
PRECIPITATION ACROSS THE WINDWARD SLOPES OF THE OLYMPICS AND
CASCADES.


RUBIN-OSTER