Prognostic Meteorological Discussion
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FXUS02 KWBC 031613
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1112 AM EST SAT DEC 03 2016

VALID 12Z TUE DEC 06 2016 - 12Z SAT DEC 10 2016

...OVERVIEW...

THE MEDIUM-RANGE PERIOD WILL BEGIN WITH A LOW PRESSURE SYSTEM
SPREADING RAIN THROUGH THE DEEP SOUTH AND INTO THE EASTERN U.S.
ARCTIC AIR WILL THEN FILTER INTO THE COUNTRY UNDER A LARGE-SCALE
COLD UPPER TROUGH.  MODELS CONTINUE TO DISAGREE UPON THE SPEED OF
THE EASTWARD PROGRESSION OF THE ARCTIC AIR MASS...BUT APPEAR TO
HAVE EDGED TOWARD THE FASTER SIDE.  BY NEXT FRIDAY...MUCH OF THE
COUNTRY SHOULD HAVE COME UNDER THE INFLUENCE OF THIS FIRST ARCTIC
OUTBREAK OF THE SEASON AS PRECIPITATION FROM THE NEXT CYCLONE
MOVES INTO THE PACIFIC NORTHWEST LATE NEXT WEEK INTO THE WEEKEND.

...MODEL EVALUATION/PREFERENCES...

WITH RESPECT TO THE LOW PRESSURE SYSTEM MOVING THROUGH THE SOUTH
INTO THE EASTERN U.S. DAYS 3-4 TUE-WED NEXT WEEK...THE GFS APPEARS
TO HAVE PERFORMED BETTER THAN THE ECMWF LATELY.  THUS...FOR THE
WPC DAYS 3 AND 4 PRESSURE FIELDS...A 70% WEIGHT HAS BEEN GIVEN TO
THE 06Z GFS/GEFS WITH THE REMAINING 30% GIVEN TO THE ECMWF.  THE
LOW IS FORECAST TO DISSIPATE AS IT REACHES THE CENTRAL
APPALACHIANS BY DAY 5 THU AS A NEW LOW INTENSIFIES AND MOVES OFF
THE MID-ATLANTIC COAST.  IN THE MEAN TIME...THE ECMWF REMAINS THE
SLOWEST REGARDING THE ARCTIC COLD FRONT MOVING THROUGH THE PLAINS
WHEREAS THE GFS REMAINS ON THE FAST SIDE.  GIVEN THE STRUCTURAL
EVOLUTION OF RECENT FRONTAL SYSTEMS IN THE PLAINS...A FASTER
PROGRESSION OF THE ARCTIC AIR MORE IN LINE WITH THE GFS SOLUTIONS
IS PREFERRED.  THE WPC DAYS 5 TO 7 PRESSURE FIELDS CONTINUE WITH A
70%-30% SPLIT BETWEEN THE 06 GEFS MEAN AND 00Z EC MEAN...MIXING IN
WITH SOME OPERATIONAL SOLUTIONS ON DAY 5.  THE CONSEQUENCE OF THIS
WILL BE A DELAYED AND WEAKER DEVELOPMENT OF A SURFACE LOW OVER THE
GREAT LAKES ON DAY 5...ALONG WITH A SLIGHTLY FASTER EASTWARD
PROGRESSION OF THE ARCTIC COLD FRONT THROUGH THE EAST COAST.

...WEATHER HIGHLIGHTS/THREATS...

THE UPR TROUGH PROGRESSING FROM WEST TO EAST ACROSS THE LOWER 48
WILL BE ACCOMPANIED BY MUCH BELOW NORMAL TEMPS... INITIALLY OVER
THE WEST/PLAINS AND THEN REACHING THE EAST.  EXPECT THE MOST
EXTREME ANOMALIES TO BE OVER THE ERN SLOPES OF THE NRN-CNTRL
ROCKIES INTO THE PLAINS TUE-THU WITH HIGHS 20-30F OR SO BELOW
NORMAL.  ANOMALIES FOR MINS SHOULD BE SOMEWHAT LESS EXTREME EXCEPT
OVER MONTANA.  AS THE COLD AIR PUSHES EWD AND SFC HIGH PRESSURE
EVENTUALLY BUILDS INTO THE SOUTHEAST THE SRN HALF OF THE EAST WILL
LIKELY BE COLDEST RELATIVE TO NORMAL WITH MINUS 10-20F ANOMALIES.
WHILE THERE IS STILL SOME UNCERTAINTY IN SFC DETAILS... OVERALL
PATTERN WILL FAVOR A PERIOD OF COLD AND BRISK CYCLONIC FLOW ACROSS
THE GRTLKS/NORTHEAST AND ENHANCED LAKE EFFECT SNOW LATE IN THE
WEEK.  AHEAD OF THE COLD AIR THERE WILL BE AN AREA OF MOSTLY RAIN
ACROSS PORTIONS OF THE EAST ON TUE.  THEN UNCERTAINTY IN FRONTAL
TIMING OVER THE EAST LEADS TO LOWER THAN DESIRED CONFIDENCE IN
DETERMINING COVERAGE/INTENSITY OF RNFL BEFORE THE COLD AIR ARRIVES.

ACROSS THE WEST... EARLY PERIOD TROUGH CROSSING THE REGION WILL
BRING SOME AREAS OF SNOW TO FAVORED TERRAIN.  THEN THE PRIMARY
EMPHASIS WILL BE ON MSTR PUSHING INTO THE NORTHWEST BY THE LATTER
HALF OF THE WEEK AND THEN EXTENDING INTO THE NRN ROCKIES.  FAVORED
LOCATIONS ALONG THE PAC NW/EXTREME NRN CA COAST AND THE CASCADES
WILL LIKELY SEE THE HIGHEST PCPN TOTALS.  WRN U.S. TEMPS WILL
MODERATE COMPARED TO TUE-WED BUT THERE SHOULD BE ENOUGH LINGERING
COLD AIR TO PRODUCE SNOW AT FAIRLY LOW ELEVS.

KONG/RAUSCH

$$




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