360  
FXUS02 KWBC 070515  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1215 AM EST THU DEC 07 2017  
 
VALID 12Z SUN DEC 10 2017 - 12Z THU DEC 14 2017  
   
..OVERVIEW
 
 
SECOND VERSE, SAME AS THE FIRST. THE WESTERN RIDGE/EASTERN TROUGH  
REMAINS LOCKED IN PLACE. THIS WILL CONTINUE THE STABLE SYNOPTIC  
PATTERN OF MILD/DRY IN THE WEST, A TRANSITION ZONE OF TEMPERATURES  
IN THE CENTRAL STATES (PLAINS TO MISSISSIPPI VALLEY), AND COLD IN  
THE EAST WITH PRECIPITATION FOCUSED MOSTLY AROUND THE GREAT LAKES  
AND THEN THE NORTHEAST NEXT WED/THU AS A POTENTIAL COASTAL STORM  
DEVELOPS.  
 
   
..GUIDANCE PREFERENCES AND PREDICTABILITY ASSESSMENTS
 
 
CONTINUED WITH A DETERMINISTIC CONSENSUS BLEND FOR THE FORECAST  
WITH A TREND TOWARD THE ENSEMBLE MEANS LATER IN THE PERIOD. THOUGH  
THE 12Z UKMET/CANADIAN WERE ON THE EXTREME SIDE OF THE ENSEMBLE  
SPREAD IN THE SHORT TERM, A MINOR WEIGHTING WITH THE GFS/ECMWF  
YIELDED A GOOD STARTING POINT AS ONE COASTAL LOW EXITS AWAY FROM  
MAINE ON SUNDAY. THEREAFTER, THE 12Z CANADIAN WAS FAVORED THROUGH  
MUCH OF THE PERIOD AS THE 12Z ECMWF YET AGAIN SHOWED A PACIFIC  
UPPER LOW TRYING TO PUNCH INTO THE RIDGE. THOUGH IT IS CERTAINLY  
POSSIBLE TO SNEAK A WEAK SYSTEM UNDERNEATH THE CORE OF POSITIVE  
HEIGHT ANOMALIES (LOCATED IN BRITISH COLUMBIA) OPTED TO DOWNPLAY  
THIS FEATURE AGAIN UNTIL MORE SUPPORT IS SEEN. THE WEAKER  
CANADIAN/GFS WERE PREFERRED THERE. BY NEXT WED/THU, GUIDANCE  
CONTINUES TO ADVERTISE A MORE ROBUST COASTAL DEVELOPMENT OFFSHORE  
THE MID-ATLANTIC WITH A TRACK JUST OFF THE NEW ENGLAND COAST. THIS  
WOULD BE A RAIN/SNOW EVENT FOR NEW ENGLAND AS IT WINDS UP INTO  
SOUTHEASTERN CANADA. ENSEMBLES HAVE BEEN CONSISTENT FOR SEVERAL  
DAYS THOUGH THIS DOES DEPEND ON SHORTWAVES STILL IN THE CENTRAL  
PACIFIC. AS SUCH, HOW THIS EVOLVES IS UNCERTAIN BUT THE 12Z  
CANADIAN OFFERED A REASONABLE SOLUTION NEAR THE CONSENSUS POSITION  
NEXT WED.  
 
   
..WEATHER HIGHLIGHTS
 
 
SEVERAL CLIPPERS WILL SWING THROUGH THE EAST WITH A RENEWED COLD  
SHOT OF CANADIAN AIR BUT GENERALLY LIGHT PRECIP -- THE EXCEPTION  
WILL BE AROUND THE GREAT LAKES AND ALONG THE TRACK OF THE NORTHERN  
STREAM SYSTEM. TEMPERATURES WILL BE ABOUT 5-20 DEGREES ABOVE  
AVERAGE IN THE WEST (OUTSIDE THE INTERIOR VALLEY AREAS OF WA/OR  
UNDER AN INVERSION) AND ABOUT 5-15 DEGREES BELOW AVERAGE IN THE  
EAST.  
 
FRACASSO  
 

 
 
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