Prognostic Meteorological Discussion
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000
FXUS02 KWBC 021601
PMDEPD

EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1100 AM EST FRI DEC 02 2016

VALID 12Z MON DEC 05 2016 - 12Z FRI DEC 09 2016

...OVERVIEW...

AN UPPER-LEVEL LOW COMING OFF FROM NORTHERN MEXICO IS EXPECTED TO
INDUCE THE DEVELOPMENT OF A LOW PRESSURE SYSTEM WHICH WILL SPREAD
RAIN FROM THE DEEP SOUTH INTO THE EASTERN U.S. EARLY NEXT WEEK.
BEHIND THIS SYSTEM...A LONGWAVE TROUGH IS FORECAST TO MOVE ACROSS
THE WESTERN U.S. AS ARCTIC AIR FROM CANADA BEGINS TO FILTER INTO
THE ROCKIES.  THEREAFTER...MODELS BEGIN TO DIVERGE REGARDING THE
DEGREE OF INTERACTION BETWEEN THE WESTERN U.S. TROUGH WITH THE
DEPARTING UPPER-LEVEL LOW IN THE EASTERN U.S.  THIS WILL DETERMINE
HOW FAR EAST THE ARCTIC AIR MASS WILL BE PUSHED EASTWARD ACROSS
THE EASTERN U.S. BY THE LATTER HALF OF NEXT WEEK.
MEANWHILE...MOISTURE FROM THE NEXT CYCLONE SHOULD BE OVERSPREADING
MUCH OF THE PACIFIC NORTHWEST INTO THE NORTHERN ROCKIES.


...MODEL EVALUATION/PREFERENCES...

MODELS HAVE COME INTO AGREEMENT THAT OF A SLOWER PROGRESSION OF
THE UPPER LOW EJECTING OUT OF NORTHERN MEXICO ON DAY 3 MONDAY
FOLLOWED BY MODEST SURFACE CYCLOGENESIS FROM THE TEXAS COAST UP
INTO THE OHIO VALLEY ON DAY 4 TUESDAY.  MODEL SOLUTIONS BEGIN TO
DIVERGE THEREAFTER AS A LONGWAVE UPPER TROUGH IN THE WESTERN U.S.
MOVES OUT INTO THE PLAINS AND INTERACTS WITH THE WEAKENING EASTERN
U.S. LOW PRESSURE SYSTEM.  THIS DISCREPANCY HAS LED TO LARGE
DIFFERENCES IN SPEED OF PROGRESSION OF THE FIRST SIGNIFICANT
ARCTIC AIR ACROSS THE U.S. THROUGH NEXT FRIDAY...WITH THE SLOWEST
00Z ECMWF REACHING ONLY THE EAST COAST BY NEXT FRIDAY WHILE THE
06Z GFS TAKES IT WELL OUT TO SEA.  THE DECISION WAS THE USE THE
00Z GFS/GEFS SOLUTION AND BLEND WITH SOME OF THE 00Z EC MEAN.


...WEATHER HIGHLIGHTS/THREATS...

AMPLIFYING TROUGH OVER THE WEST DURING THE FIRST PART OF THE WEEK
WILL SPREAD AREAS OF PCPN ACROSS PORTIONS OF THE REGION.  SNOW
LVLS WILL BE ON THE LOW SIDE.  AFTER A BREAK HEAVIER PCPN SHOULD
REACH THE NRN-CNTRL WEST COAST DURING THE LATTER HALF OF THE WEEK
WITH SOME OF THIS MSTR REACHING THE NRN ROCKIES.  LINGERING COLD
AIR MAY SUPPORT SOME POTENTIAL OF WINTRY PCPN AT FAIRLY LOW ELEVS.
 AS MID LVL ENERGY/SFC LOW PRES HEAD INTO THE PLAINS/GRTLKS ONE OR
MORE AREAS OF SNOW ARE PSBL IN THE COLD SECTOR.  FARTHER SEWD HVY
RNFL IS PSBL OVER THE SOUTHEAST/SRN MID ATLC IN ASSOC WITH THE
SHORT RANGE UPR LOW EJECTING FROM NRN MEXICO... WITH SOMEWHAT
LIGHTER ACTIVITY ELSEWHERE.  CONSULT LATEST SPC OUTLOOKS FOR
FURTHER DETAILS ON SEVERE WEATHER POTENTIAL THAT MAY EXIST OVER
SRN AREAS.  COMBINATION OF STRONG HIGH PRES BUILDING SEWD FROM
CANADA AND THEN POTENTIALLY STRONG GRTLKS-NORTHEAST LOW PRES LATER
IN THE PERIOD MAY GENERATE STRONG WINDS.  COLD CYCLONIC FLOW UNDER
THE CORE OF THE UPR TROUGH WILL LIKELY SUPPORT AREAS OF LAKE
EFFECT SNOW LATE NEXT WEEK.

FCST REMAINS ON TRACK FOR WELL BELOW NORMAL TEMPS ACROSS MUCH OF
THE WRN-CNTRL STATES... REACHING ERN AREAS LATE IN THE PERIOD.
EXPECT ONE OR MORE DAYS WITH HIGHS 20-30F BELOW NORMAL ALONG THE
ERN SLOPES OF THE ROCKIES INTO THE NRN-CNTRL PLAINS TUE-THU.
TOWARD THE LATTER HALF OF THE WEEK TEMPS SHOULD TREND WARMER OVER
THE WEST WHILE MINUS 10-20F ANOMALIES FOR HIGHS REACH THE ERN
STATES.  MIN TEMPS COULD DECLINE TO OR BELOW FREEZING ALONG/NEAR
PORTIONS OF THE GULF COAST BY NEXT FRI.

KONG/RAUSCH

$$




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