712  
FXUS02 KWBC 011558  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1057 AM EST MON JAN 01 2018  
 
VALID 12Z THU JAN 04 2018 - 12Z MON JAN 08 2018  
   
..OVERVIEW/GUIDANCE ASSESSMENT AND PREFERENCES
 
 
THE MEDIUM RANGE PERIOD STARTS OUT WITH DEEP TROUGHING ACROSS THE  
EASTERN STATES AND A RAPIDLY DEEPENING CYCLONE IN THE WESTERN  
ATLANTIC WITH SHORTWAVE ENERGY MOVING INTO THE WEST. EVENTUALLY  
THIS PATTERN TRANSITIONS INTO MORE ZONAL/MEAN FLOW ACROSS THE  
LOWER 48 WITH BUILDING TROUGHING OFFSHORE IN THE PACIFIC BY THE  
END OF THE PERIOD.  
 
REGARDING THE MODELS, THERE IS FAIRLY GOOD AGREEMENT ON THE  
OVERALL PATTERN THROUGH DAY 5...WITH DIFFERENCES, PARTICULARLY IN  
THE DETAILS, ARISING THEREAFTER. THE BIGGEST DIFFERENCES EXIST  
WITH EVENTUAL PROGRESSION OF SHORTWAVE ENERGY INTO THE WEST EARLY  
IN THE PERIOD AND BUILDING TROUGHING ACROSS THE EASTERN PACIFIC BY  
DAY 7. THE OPERATIONAL GFS IS THE QUICKEST TO PROGRESS SHORTWAVE  
ENERGY INTO THE WEST AND ALSO THE QUICKEST/FARTHEST EAST OF THE  
OPERATIONAL RUNS WITH TROUGHING/POSSIBLE CLOSED LOW SOMEWHERE OFF  
THE SOUTHWEST COAST BY DAY 7. RUN TO RUN VARIABILITY IN THE MODELS  
HOWEVER IS PARTICULARLY HIGH SO CONFIDENCE IN ANY PARTICULAR  
SOLUTION AT THIS POINT IS VERY LOW. FOR THIS REASON, THIS CYCLE OF  
THE WPC PROGS STUCK WITH A BLEND OF PREVIOUS SHIFT CONTINUITY AND  
THE OPERATIONAL ECMWF/GFS DAYS 3 AND 4, EVENTUALLY TRANSITIONING  
TO A MOSTLY EC MEAN/GEFS MEAN BLEND WITH CONTINUITY BY DAY 7.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
CONFIDENCE CONTINUES TO INCREASE THAT PORTIONS OF NEW ENGLAND  
SHOULD SEE FAIRLY SIGNIFICANT SNOWFALL FROM A RAPIDLY DEEPENING  
CYCLONE EXPECTED TO TRACK FROM THE WESTERN ATLANTIC INTO THE  
CANADIAN MARITIMES THURSDAY INTO FRIDAY, WITH A PERIOD OF STRONG  
WINDS ACROSS THE NORTHEAST CAUSING BLOWING SNOW AND DANGEROUSLY  
COLD WIND CHILLS. THERE IS ALSO SOME POTENTIAL FOR SNOWFALL ALONG  
THE MID-ATLANTIC COAST WITH AMOUNTS VERY SENSITIVE TO THE EXACT  
TRACK OF THE LOW. BEHIND THE SYSTEM, MUCH OF THE EASTERN HALF OF  
THE COUNTRY WILL SEE VERY COLD TEMPERATURES WITH AFTERNOON HIGH  
VALUES INTO THE WEEKEND AS MUCH AS 20 TO 30 DEGREES BELOW NORMAL,  
WITH RECORD LOWS POSSIBLE. FROM SUNDAY ONWARD, TEMPERATURES ACROSS  
THE EAST SHOULD MODERATE FROM WEST TO EAST AS PACIFIC FLOW  
EVENTUALLY PUSHES INTO THE REGION.  
 
ELSEWHERE, THE WESTERN U.S. SHOULD SEE A MORE UNSETTLED PERIOD, AS  
WEAKENING SHORTWAVE ENERGY PROMOTES RAIN/MOUNTAIN SNOWS ACROSS THE  
PACIFIC NORTHWEST...WITH SOME OF THIS MOISTURE ALSO EXTENDING  
EASTWARD INTO THE ROCKIES. PROGRESSION OF THIS FLOW ALOFT SHOULD  
BRING A FRONTAL SYSTEM INTO THE EAST-CENTRAL U.S. BY THE START OF  
NEXT WEEK, WITH AN INCREASE IN PRECIPITATION POTENTIAL FROM THE  
PLAINS/MISSISSIPPI VALLEY AND EASTWARD. EXPECT SNOWFALL IN THE  
NORTHERN LATITUDES OF THE UPPER MIDWEST AND GREAT LAKES, WITH RAIN  
ACROSS THE SOUTHERN REGIONS, AND A TRANSITION ZONE SOMEWHERE IN  
BETWEEN. ACROSS CALIFORNIA AND THE SOUTHWEST, THERE IS SOME  
POTENTIAL FOR AN INCREASE IN PRECIPITATION BY DAY 7 BUT HOW MUCH  
OF THIS MOISTURE MAKES IT ONSHORE BY DAY 7 IS STILL IN QUESTION  
DUE TO MODEL DIFFERENCES IN THE UPPER TROUGHING OFFSHORE.  
 
SANTORELLI  
 

 
 
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