586  
FXUS02 KWBC 201601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1101 AM EST TUE NOV 20 2018  
 
VALID 12Z FRI NOV 23 2018 - 12Z TUE NOV 27 2018  
   
..OVERVIEW
 
 
A VERY STRONG CLOSED HIGH NORTH OF ENGLAND IS FORECAST TO  
RETROGRADE WESTWARD ACROSS SOUTHERN GREENLAND LATER THIS WEEK AND  
SETTLE OVER NORTHERN QUEBEC, FAVORING BLOCKED TROUGHING OVER THE  
EASTERN THIRD OF THE LOWER 48. IN THE WEST, TROUGHING WILL PASS  
THROUGH LATE THIS WEEK AND BE REPLACED BY RIDGING SUNDAY-MONDAY  
AHEAD OF ANOTHER SYSTEM NEXT TUESDAY.  
 
   
..GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
THE LATEST GUIDANCE REMAINS IN FAIRLY GOOD AGREEMENT WITH THE  
OVERALL LARGE-SCALE PATTERN, KEEPING A TROUGH OVER MUCH OF THE  
EAST COAST AND WITH RIDGING REPLACING THE TROUGH OVER THE WEST.  
SPECIFICS WITH INDIVIDUAL SHORTWAVES WITHIN THE MEAN FLOW CONTINUE  
TO VARY IN REGARDS TO AMPLITUDE AND LOCATION. THE CURRENT GFS  
SOLUTION HAS TRENDED TOWARD THE 00Z ECWMF, ESPECIALLY WITH THE  
CYCLONE THAT WILL DEVELOP OVER THE CENTRAL U.S. AND LIFT AS A  
NOR'ESTER UP THE MID-ATLANTIC REGION. EVEN WITH THE DIFFERENCES,  
USING A DETERMINISTIC BLEND SERVED WELL FOR THE BEGINNING OF THE  
EXTENDED PERIOD- WITH HEAVIER WEIGHTING OF THE ECWMF AND GFS WITH  
LESSER WEIGHTING OF THE UKMET AND CMC. BY DAY 7 (MONDAY) THE RATIO  
WAS ABOUT 70% OF THE ABOVE BLEND AND 30% EC ENSEMBLE MEANS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
CONTINUED WET FOR THE WEST AS THE SECOND OF TWO SYSTEMS (THE FIRST  
IN THE SHORT RANGE) MOVES THROUGH ON FRIDAY/SATURDAY WITH PLENTY  
OF SNOW AT HIGHER ELEVATIONS. ADDITIONAL PRECIPITATION WILL BE  
LIKELY NEXT WEEK AHEAD OF THE NEXT PACIFIC SYSTEM, BUT FAVORED  
OVER COASTAL AREAS OF WA/OR BY THEN. IN THE EAST, LEAD SYSTEM ON  
FRIDAY WILL TAP THE GULF FOR MOISTURE AND EVEN AS THE NORTHERN  
FRONT WEAKENS INTO THE GREAT LAKES, PRECIPITATION WILL EXPAND  
EASTWARD AS THE GULF SURFACE LOW ORGANIZES. RAIN WILL SPREAD  
NORTHEASTWARD WITH SOME WINTRY WEATHER ON THE NORTH AND NORTHEAST  
SIDE AS THE COLD AIRMASS RETREATS (MODELS REALLY STRUGGLE WITH  
THIS EVOLUTION). HEAVIEST RAIN MAY BE ALONG THE I-81/I-95 CORRIDOR  
FROM SC UP TO THE MID-ATLANTIC TO THE NORTHWEST OF THE SURFACE LOW  
TRACK. WILL GET ONLY A BRIEF RESPITE AHEAD OF THE NEXT SYSTEM  
LIFTING INTO THE LAKES WHICH HAS THE POTENTIAL TO BE SLOWER AND  
STRONGER THAN THE PREVIOUS SYSTEM AS IT GETS BLOCKED FROM A  
TYPICAL EXIT THROUGH SOUTHEASTERN CANADA.  
 
THE BELOW/WELL-BELOW NORMAL TEMPERATURES ACROSS THE NORTHEAST  
PORTION OF THE COUNTRY WILL MODERATE BY THIS COMING WEEKEND. COLD  
CANADA AIR WILL FILTER INTO THE CENTRAL PORTION OF THE U.S.,  
RESULTING IN MAXIMUM TEMPERATURE NEGATIVE ANOMALIES (5-15F BELOW  
AVERAGE) FROM THE ROCKIES EASTWARD.  
 
CAMPBELL/FRACASSO  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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