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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 1600Z Dec 08, 2017)
 
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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
1100 AM EST FRI DEC 08 2017

VALID 12Z MON DEC 11 2017 - 12Z FRI DEC 15 2017

...A MIDWEST/GREAT LAKES THROUGH NORTHEASTERN U.S. HEAVY SNOW
THREAT...


...PATTERN OVERVIEW/PREDICTABILITY ASSESSMENT/PREFERENCES...

THE SYNOPTIC-SCALE PATTERN IS HIGHLIGHTED BY A MEAN UPPER TROUGH
EAST OF THE PLAINS. MULTIPLE EMBEDDED SHORTWAVES ROTATE WITHIN THE
DEEP CYCLONIC FLOW FOSTER DEVELOPMENT OF SEVERAL SURFACE WAVES.
500MB HEIGHT ANOMALIES ARE IN THE 2-3 STANDARD DEVIATION BELOW
AVERAGE AS THE OPPOSITE PHASE DOMINATES THE WRN U.S.

00 UTC GEFS/ECMWF ENSEMBLES OFFER A WELL CLUSTERED FORECAST
SOLUTION INTO DAY 6 OR SO THAT MAINTAINS MAX WPC CONTINUITY AND
FORECAST CONFIDENCE. A FAVORED COMPOSITE SOLUTION LOCKS IN A FULL
LATITUDE WRN NORTH AMERICAN RIDGE/ERN NORTH AMERICAN TROUGH
PATTERN ALOFT. THE 00 UTC GEFS MAINTAINS THE WRN NOAM RIDGE MORE
THAN THE 06 UTC GFS/00 UTC ECMWF ENSEMBLES DAY7/NEXT FRI AND THAT
MAY BE A PRUDENT WAY TO GO GIVEN INITIAL AMPLITUDE. THIS WILL
CONTINUE A SYNOPTIC PATTERN OVER THE U.S. WITH MILD/DRY CONDITIONS
IN THE WEST...A TRANSITION ZONE OF TEMPS IN THE PLAINS TO MS
VALLEY...AND COLD FLOW INTO THE ERN THIRD OF THE NATION WHERE
HEAVY SNOW POTENTIAL WILL FOCUS FROM THE MIDWEST/GREAT LAKES TO
THE NRN MID-ATLANTIC/NORTHEAST. DETERMINITSIC MODELS OFFER BETTER
DETAIL BUT LESS RUN TO RUN CONTINUITY.


...WEATHER HIGHLIGHTS/THREATS...

THE PERSISTENT HIGH AMPLITUDE PATTERN OVER THE NATION...ABOVE
NORMAL TEMPS REMAINS A FIXTURE OVER THE WRN U.S. WHILE COLD
READINGS WILL DOMINATE EAST OF THE PLAINS. WHILE NO WIDESPREAD
DAILY TEMPERATURES RECORDS SHOULD BE BROKEN...EXPECT ANOMALIES IN
THE 10 TO 15 DEGREES ABOVE/BELOW NORMAL TO BE COMMONPLACE OVER
THESE RESPECTIVE REGIONS. OVER SECTIONS OF THE NWRN U.S. INTO THE
CENTRAL GREAT BASIN...UPPER/SURFACE RIDGING HELPS MAINTAIN A
SEMI-PERMANENT LOW-LEVEL TEMP INVERSION. THUS...THESE LOCATIONS
MAY STRUGGLE TO REACH SOME OF THE WARMER TEMPERATURES ACROSS
SURROUNDING AREAS. OVER THE SWRN U.S...OFFSHORE SURFACE GRADIENTS
IN RESPONSE TO INTERIOR HIGH PRESSURE MAY BRING FURTHER FIRE
WEATHER CONCERNS TO SRN CA. A BIG STORY REMAINS A SNOWFALL THREATS
FROM THE UPPER MIDWEST TO THE GREAT LAKES/OH VALLEY AND NERN U.S.
COLD CYCLONIC FLOW OVER THE MILD GREAT LAKES WILL INVIGORATE HEAVY
SNOW SHOWERS DOWNWIND. DEPENDING ON LOW DEPTH/PLACEMENT...A
CONSIDERABLE SNOWFALL THREAT EXISTS FROM THE UPPER MIDWEST TO
ESPECIALLY THE NERN STATES WITH TUE/WED.

SCHICHTEL