903  
FXUS02 KWBC 030630  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
130 AM EST SUN DEC 03 2017  
 
VALID 12Z WED DEC 06 2017 - 12Z SUN DEC 10 2017  
   
..MILD AND DRY IN THE WEST BUT COLD AND WINTRY IN THE EAST
 
 
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
AN IMPRESSIVE RIDGE/TROUGH PATTERN WILL BE FIRMLY IN PLACE OVER  
THE LOWER 48 NEXT WEEK AS COLDER CANADIAN AIR SPILLS DOWN INTO THE  
CENTRAL/EASTERN STATES WHILE THE WEST ENJOYS A MILD AND DRY  
STRETCH. THE DETERMINISTIC MODELS AGREE WITH THE MULTI-CENTER  
ENSEMBLE CONSENSUS ON THE SYNOPTIC PATTERN FOR MUCH OF THE WEEK  
BUT WITH EXPECTED DIFFERENCES IN SOME DETAILS (E.G. SYSTEM TIMING,  
TRACK, AND STRENGTH). A BLEND OF THE RECENT GFS/ECMWF/UKMET SERVED  
AS A GOOD STARTING POINT FOR THE WED-FRI FORECAST AS A LEAD COLD  
FRONT AND REINFORCING ARCTIC FRONT PUSH THROUGH THE EASTERN US. BY  
LATE FRIDAY INTO THE WEEKEND THE FORECAST AMONG THE GUIDANCE  
DIFFERS IN TWO AREAS: 1) UPPER MIDWEST/GREAT LAKES - HOW THE  
EMBEDDED SHORTWAVES RACE THROUGH THE TROUGH IN THE EAST AND  
WHETHER OR NOT THEY WILL AMPLIFY INTO THE NORTHEAST/NEW ENGLAND  
AND 2) OFF THE SOUTHEAST/MID-ATLANTIC COAST AS THE LEAD COLD FRONT  
LINGERS OFFSHORE AND POSSIBLE WAVES OF LOW PRESSURE (OR ONE  
CONSOLIDATED ONE) MOVE NORTHEASTWARD OR NORTHWARD NEAR THE COAST,  
POSSIBLY SPREADING RAIN/SNOW ALONG THE COAST. AS THE MODELS  
CONTINUE TO WAVER ON THE SCENARIOS, TRENDED MORE TOWARD THE  
ENSEMBLE MEANS FOR NEXT SAT/SUN WHICH STILL KEEPS THE FRONTAL ZONE  
JUST OFFSHORE AS A CLIPPER ONLY MODESTLY AMPLIFIES THROUGH THE  
OHIO VALLEY FRI/SAT. BOTH BEAR WATCHING. THOUGH ALL OF THIS, THE  
LAKE EFFECT MACHINE WILL BE IN FULL FORCE WITH A MULTI-DAY EVENT  
FOR MOST DOWNWIND LOCATIONS, THOUGH NOT A CONTINUOUS EVENT AT ANY  
GIVEN LOCATION AS THE WIND DIRECTION SHIFTS AROUND.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
MILD TEMPERATURES AHEAD OF THE LEAD FRONT ON WEDNESDAY ALONG THE  
EAST COAST (ABOUT 10-15 DEGREES ABOVE AVERAGE) WILL BE REPLACED BY  
MODIFIED ARCTIC AIR WITH TEMPERATURES ABOUT 5-15 DEGREES BELOW  
AVERAGE FOR THURSDAY AND BEYOND. ALONG AND WEST OF THE ROCKIES,  
TEMPERATURES WILL MODERATE TO ABOUT 5-10 DEGREES ABOVE AVERAGE AS  
STRONG HIGH PRESSURE REMAINS ANCHORED OVER THE GREAT BASIN. THE  
EXCEPTION MAY BE OVER INTERIOR OREGON/WASHINGTON WITH THE STABLE  
AIRMASS AND INVERSION THAT MAY KEEP TEMPERATURES BELOW AVERAGE.  
FARTHER SOUTH, DRY/WINDY CONDITIONS FOR SOUTHERN CALIFORNIA MAY  
PROLONG THE FIRE THREAT -- PLEASE CONSULT THE LATEST SPC FIRE  
WEATHER OUTLOOK.  
 
THE MOST CONCENTRATED PRECIPITATION WILL EXIT THE EAST COAST AS  
THE LEAD FRONT MOVES INTO THE ATLANTIC. EXPECT A DECREASE IN  
COVERAGE OF RAIN/SNOW AS COLDER/DRIER AIR TAKES HOLD. THE  
EXCEPTIONS WILL BE ALONG THE GULF COAST AS THE RAIN WILL TAKE A  
BIT LONGER TO EASE SOUTHWARD INTO THE GULF AND ALSO AROUND THE  
GREAT LAKES WHERE LAKE-EFFECT SNOW WILL BE A DAILY OCCURRENCE.  
TOTAL ACCUMULATIONS MAY BE SUBSTANTIAL FOR SOME FAVORED AREAS.  
ADDITIONAL LIGHT SNOW WILL BE POSSIBLE WITH CLIPPER SYSTEMS DIVING  
OUT OF CANADA ANYWHERE FROM THE HIGH PLAINS AND UPPER MIDWEST INTO  
THE OHIO/TN VALLEY AND INTO THE APPALACHIANS (MAYBE SPILLING OVER  
TOWARD THE I-95 CORRIDOR TOO). THE FRONT OFFSHORE MAY THROW SOME  
PRECIPITATION BACK TO THE NORTHWEST SHOULD A SURFACE WAVE DEVELOP  
ALONG IT AND MOVE CLOSE ENOUGH TO THE MID-ATLANTIC AND/OR NEW  
ENGLAND. THIS WOULD MEAN A THREAT OF AT LEAST SOME RAIN/SNOW TO  
THE MID-ATLANTIC AND NORTHEAST LATE IN THE WEEK -- MAYBE THE FIRST  
FLAKES FOR SOME IN THE I-95 URBAN CORRIDOR?  
 
FRACASSO  
 

 
 
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