591  
FXUS02 KWBC 090538  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1237 AM EST TUE JAN 09 2018  
 
VALID 12Z FRI JAN 12 2018 - 12Z TUE JAN 16 2018  
 
...WINTRY MIX FOR PARTS OF THE MIDWEST INTO THE NORTHEAST  
FRIDAY/SATURDAY...  
 
...ICING HAZARD JUST ALONG/NORTH OF THE OHIO RIVER INTO UPSTATE  
NEW YORK/NEW ENGLAND...  
 
   
..OVERVIEW
 
 
A WESTERN RIDGE AND EASTERN TROUGH PATTERN WILL RE-ESTABLISH  
ITSELF OVER THE CONUS BY THIS WEEKEND WHICH SUPPORTS A WINTRY MESS  
ALONG/NORTH OF THE I-70 CORRIDOR FROM SOUTHERN ILLINOIS TO  
PITTSBURGH FRIDAY THEN INTO THE NORTHEAST SATURDAY. A QUIETER  
PERIOD WILL ENSUE FOR SUN-TUE IN THE EAST BUT THE NORTHWEST WILL  
EVENTUALLY SEE ANOTHER SYSTEM AS THE RIDGE BEGRUDGINGLY GETS  
SHUNTED EASTWARD.  
 
   
..GUIDANCE ASSESSMENT AND PREFERENCES
 
 
FOCUS WILL BE ON THE DEVELOPING EASTERN SYSTEM FRI-SAT AS IT LIFTS  
OUT OF THE DEEP SOUTH AND INTO THE CENTRAL APPALACHIANS. 12Z/18Z  
GFS CONTINUED TO BE QUICKER THAN THE REST OF THE MODELS AND  
ENSEMBLES AND IT WAS NOT INCLUDED IN THE BLENDED STARTING POINT.  
USED THE 12Z ECMWF/CANADIAN/UKMET WITH THE 18Z GEFS MEAN AND 12Z  
ECMWF ENSEMBLE MEAN WHICH HAVE COME NICELY TOGETHER AS OF THE 12Z  
ECMWF. THOUGH THERE REMAINS SOME MORE ADJUSTMENT, THE ENSEMBLE  
CONSENSUS TAKES THE LOW FROM THE VA/WV LINE TO ATLANTIC CITY TO  
THE GULF OF MAINE BY SUNDAY MORNING, WHICH MAINTAINS CONTINUITY  
WELL WITH ONLY SOME DETAIL DIFFERENCES. HOWEVER, THIS WILL HAVE  
BIG IMPLICATIONS ON PRECIPITATION TYPE AND WILL NEED TO BE REFINED  
IN FUTURE RUNS.  
 
FOR NEXT MON/TUE, ECMWF ENSEMBLE MEAN WAS QUICKER TO MOVE THE  
RIDGE AXIS EASTWARD TO IDAHO THAN THE DETERMINISTIC CONSENSUS AND  
THE GEFS/CANADIAN ENSEMBLE MEANS. ITS TREND HAS BEEN SLOWER, SO  
OPTED TO PUT MORE WEIGHT IN THE GEFS MEAN FOR THE MON/TUE  
FORECAST. THIS WOULD KEEP A PACIFIC FRONT JUST OFFSHORE UNTIL  
TUESDAY, BUT PRECIPITATION WILL PRECEDE IT. TO THE EAST, A CLIPPER  
SYSTEM FROM CANADA MAY DIVE DOWN THROUGH THE MIDWEST INTO THE  
EAST/SOUTH IN A RATHER DRY ENVIRONMENT.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
SIGNAL FOR A MIXED PRECIPITATION EVENT HAS BEEN CONSISTENT FOR  
SEVERAL DAYS IN THE ZONE JUST TO THE NORTH OF THE SFC LOW AND  
ATTENDANT FRONT TO ITS NORTHEAST AS COLDER AIR BEHIND THE LEAD  
COLD FRONT TO THE NORTH ON FRIDAY OOZES SOUTHWARD. MODELS AND  
ENSEMBLES HAVE SHOWN THE POTENTIAL FOR AT LEAST A QUARTER INCH OF  
ICE IN BETWEEN PLAIN COLD RAIN TO THE SOUTH AND SLEET TO THE NORTH  
WITH SNOW FARTHER NORTH IN THE DEEPER COLD AIR. THOUGH THE SURFACE  
HIGH WILL BE LOCATED TO THE NW OF THE LOW AND NOT THE NORTH, THE  
TEMPERATURE GRADIENT SHOULD BE RATHER STEEP -- 60S SOUTHEAST OF  
THE LOW TO 10S ACROSS THE GREAT LAKES -- AND THE MODELS HAVE BEEN  
SHOWING HIGHER PRESSURES ACROSS ONTARIO/QUEBEC (NOTE THE CHANGE IN  
THE ECMWF OVER THE PAST FEW RUNS). NOT TO BE LOST WILL BE LOCALLY  
HEAVY RAIN OVER SOUTHERN NEW ENGLAND DUE TO 1) A VORTICITY  
SPIN-OFF THAT SURGES NORTHWARD ALONG THE COAST DRAGGING UP HIGH PW  
AIR (VALUES AROUND 1.50 INCHES WHICH IS +3 TO +4 STANDARD  
DEVIATIONS) AND 2) THE COLD FRONT THAT WILL STALL OVER THE AREA ON  
SATURDAY AHEAD OF THE APPROACHING LOW PRESSURE. HIGHEST ENSEMBLE  
PROBABILITIES LIE ACROSS SOUTHERN NEW ENGLAND UP INTO THE MAINE  
COAST.  
 
TEMPERATURES WILL BE QUITE VARIABLE OVER THE EASTERN CONUS --  
10-25 DEGREES ABOVE AVERAGE AHEAD OF THE FRONT IN THE EAST WHERE  
RECORD HIGH MINIMUM TEMPERATURES ARE LIKELY BUT 10-20 DEGREES  
BELOW AVERAGE BEHIND THE FRONT. OVERNIGHT TEMPERATURES WILL BE  
MORE TYPICAL FOR LATE APRIL OR EARLY MAY IN THE NORTHEAST ON  
FRIDAY. BY NEXT WEEK, BELOW AVERAGE TEMPERATURES WILL BE LIKELY  
NEARLY EVERYWHERE EAST OF THE ROCKIES THANKS TO TROUGHING AND  
CANADIAN HIGH PRESSURE. THE WEST WILL SEE RELATIVELY MILD  
TEMPERATURES -- UP TO ABOUT 15 DEGREES ABOVE AVERAGE.  
 
FRACASSO  
 

 
 
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