800  
FXUS02 KWBC 280644  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
143 AM EST SUN JAN 28 2018  
 
VALID 12Z WED JAN 31 2018 - 12Z SUN FEB 04 2018  
 
...A WINTRY WEATHER THREAT FOR THE NWRN US/ROCKIES AND INTO THE  
ERN US...  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM A  
COMPOSITE OF THE 18 UTC GEFS MEAN...12 UTC ECMWF ENSEMBLE  
MEAN...AND WPC CONTINUITY. THIS SEEMS PRUDENT CONSIDERING THE  
ABOVE NORMAL LOCAL FORECAST SPREAD WITH THE MAIN WEATHER/THREAT  
FOCUSING FEATURES DESPITE REASONABLY SIMILAR GFS/GEFS MEAN AND  
ECMWF/ECMWF ENSEMBLE MEAN LARGER SCALE FLOW EVOLUTIONS. THE 00 UTC  
GFS/ECMWF HAVE TRENDED THE LAST FEW NIGHTS TOWARD THE ENSEMBLE  
MEAN COMPOSITE...AT LEAST TEMPORARILY BOLSTERING FORECASTER  
CONFIDENCE.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
A POTENT LEAD SHORTWAVE TROUGH ENERGY/HEIGHT FALLS PUNCHES  
PROGRESSIVELY OUT FROM THE NWRN US TO THE N-CENTRAL US BY MIDWEEK.  
WEAKER UPSTREAM IMPULSES WILL SUPPORT ADDITIONAL PERIODS OF MODEST  
PRECIPIATION INCLUDING HEAVIER TERRAIN ENHANCED SNOWS ACROSS THE  
NWRN US AND ESPECIALLY THE NRN ROCKIES WITH ADDED NRN STREAM  
IMPULSES OF UNCERTAIN TIMINGS.  
 
DOWNSTREAM...A MAIN FRONT REACHES THE GREAT LAKES  
WED/THU...DRAGGING A TRAILING COLD FRONT THROUGH THE PLAINS AND  
INTO THE LOWER MS/OH VALLEY. THE SFC LOW CENTER WILL TRACK THROUGH  
SRN CANADA WITH MOST OF THE PRECIPITATION TO START...BUT INCREASED  
GULF MOISTURE WILL SUPPORT AN EXPANDED PRECIPITATION AREA  
ALONG/AHEAD OF THE COLD FRONT WED/THU ACROSS THE E-CENTRAL  
STATES/SOUTHEAST. MODELS HAVE THEN BEEN SHOWING VARYING DEGREES OF  
SFC WAVE DEVELOPMENT OUT OF THE LOWER MS VALLEY NORTHEASTWARD  
THROUGH THE MID-ATLANTIC ON FRIDAY THEN INTO THE ATLANTIC SATURDAY  
OFF THE NEW ENG COAST. AS SUCH DEVELOPMENT IS SENSITIVE TO SMALLER  
SCALE FEATURES WITH LONG LEAD TIMES...ENSEMBLE TRENDS WILL REMAIN  
MORE USEFUL FOR THE NEXT FEW DAYS THAN ANY GIVEN DETERMINISTIC  
RUN. ENOUGH COLD AIR SHOULD BE IN PLACE TO THE NORTH OF THE FRONT  
TO SUPPORT A WIDESPREAD SWATH OF POTENTIALLY HEAVY SNOW PARALLEL  
TO ANY SFC LOW TRACK OR AT LEAST PARALLEL TO THE UPPER TROUGH AXIS  
PROPAGATION.  
 
SCHICHTEL  
 

 
 
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