086  
FXUS02 KWBC 280645  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
145 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.  
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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