363  
FXUS02 KWBC 280721  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
220 AM EST THU DEC 28 2017  
 
VALID 12Z SUN DEC 31 2017 - 12Z THU JAN 04 2018  
 
...ARCTIC AIR WILL CONTINUE ITS DOMINANCE EAST OF THE ROCKIES WELL  
INTO THE NEW YEAR...  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT..
 
 
MODELS AND ENSEMBLES THAT WERE HIGHLY VARIED OVER THE PAST FEW  
DAYS SEEM TO BE CONVERGING UPON A BETTER CLUSTERED OVERALL  
SOLUTION WITH THE LATEST COUPLE OF RUNS. THIS BOLSTERS FORECAST  
CONFIDENCE TO NEAR AVERAGE LEVELS...ALBIET WITH CONTINUED STANDARD  
DIFFERENCES WITH THE TIMING OF SMALLER SCALE EMBEDDED SYSTEMS.  
GUIDANCE SHOWS AN AMPLIFIED PATTERN HIGHLIGHTED BY A MID-UPPER  
LEVEL RIDGE ON THE WEST COAST OF NORTH AMERICA AND A COLD TROUGH  
OVER CENTRAL AND ERN NORTH AMERICA. THE WPC MEDIUM RANGE PRODUCT  
SUITE WAS DERIVED FROM A BLEND OF GEFS/NAEFS/ECMWF ENSEMBLES AND  
CONTINUITY...WITH SMALLER INPUT FROM THE GFS/ECMWF.  
   
..WEATHER HIGHLIGHTS/THREATS
 
 
MULTIPLE SHOTS OF REINFORCING ARCTIC AIR WILL ENSURE FRIGID  
TEMPERATURES OVER THE NATION FROM THE ROCKIES TO THE SRN AND ERN  
U.S. OVER THE NEXT WEEK AS COLD HIGH PRESSURE SETTLES TO THE EAST  
OF A SHARP QUASI-STATIONARY FRONT BANKING UP AGAINST THE ROCKIES.  
PERIODIC SURGES OF COLD CYCLONIC FLOW OVER THE GREAT LAKES WILL  
FAVOR LAKE EFFECT SNOWS...PROLONGING AN ACTIVE RECENT PATTERN. THE  
AMPLIFIED NATURE OF THE CENTRAL AND ERN NORTH AMERICAN MEAN TROUGH  
ALOFT ALSO LENDS SOME POTENTIAL FOR SOME DEEPENED IMPULSE TO LIFT  
SYSTEM ENERGY AND MORE ORGANIZED WINTER WEATHER FROM THE ERN  
MID-ATLANTIC UP INTO NEW ENG. THE 00 UTC ECMWF OFFERS ONE MINORITY  
GUIDANCE EXAMPLE OF SUCH A THREAT ONLY HINTED AT IN THE EARLIER  
ISSUED WPC PRODUCT SUITE. MEANWHILE...ANY MOISTURE RETURN WITH  
IMPULSE PASSAGES WOULD BRING AN INTERIOR SRN/SERN US ICE/SNOW  
THREAT...WITH MODEST RAINS CLOSER TO THE GULF COAST/FL. OUT  
WEST...CA AND THE S-CENTRAL INTERIOR/SWRN US WILL STAY ON THE MILD  
SIDE...BUT SHORTWAVE TROUGH PASSAGES FAVOR SWATHS OF WINTERY  
PRECIPITATION FROM THE NWRN U.S. TO THE NRN ROCKIES.  
 
SCHICHTEL  
 

 
 
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