384  
FXUS02 KWBC 221601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST THU NOV 22 2018  
 
VALID 12Z SUN NOV 25 2018 - 12Z THU NOV 29 2018  
 
...MIDWEST TO GREAT LAKES/NORTHERN NEW ENGLAND WINTER WEATHER  
THREAT...   
..MORE WET WEATHER FROM THE NORTHWEST INTO CALIFORNIA
 
 
   
..OVERVIEW
 
 
MODELS AND ENSEMBLES OVERALL AGREE TO SHOW AN ACTIVE PATTERN NEXT  
WEEK FOR THE NORTHERN CORNERS OF THE LOWER 48 NEXT WEEK AS  
TROUGHING ALOFT SETTLES INTO THE MIDWEST/GREAT LAKES AND PACIFIC  
SYSTEMS PUSH INTO WA/OR AND THROUGH NORTHERN CA. A LEAD SYSTEM  
PROVIDES A SIGNIFICANT WINTER WEATHER THREAT ON ITS NORTH SIDE  
FROM THE MID-MS VALLEY NORTHEASTWARD OVER THE GREAT LAKES AND  
NORTHERN NEW ENGLAND SUNDAY INTO MIDWEEK. PERIODS OF ENHANCED  
RAINS/ELEVATION SNOWS WILL ALSO BE ON THE INCREASE FOR THE  
NORTHWEST AND INTO CA NEXT WEEK.  
 
...GUIDANCE/UNCERTAINTY ASSESSMENT AND WEATHER  
HIGHLIGHTS/THREATS...  
...  
 
LATEST GEFS AND ECMWF ENSEMBLE MEANS PROVIDE A GOOD STARTING POINT  
TO THE FORECAST FOR THE SUN-TUE PERIOD, WITH LINGERING  
TIMING/AMPLITUDE DIFFERENCES ESPECIALLY OVER THE EASTERN THIRD OF  
THE NATION STILL MORE RAMPANT IN THE DETERMINISTIC MODELS.  
 
A LEAD SYSTEM HAS HAD QUITE POOR CONSISTENCY IN THE GUIDANCE NEAR  
SOUTHERN NEW ENGLAND ON SUNDAY AS AN INITIAL TROUGH EXITS THE  
COAST WITH A SOUTHERN SYSTEM EXITING THROUGH BERMUDA. AGAIN TRIED  
TO STAY NEAR THE ENSEMBLE MEAN CONSENSUS, BUT THE DETERMINISTIC  
MODELS HAVE NOT SETTLED ONTO A COMMON SOLUTION. THIS WOULD SUPPORT  
SOME HEAVIER COASTAL RAINS AND INTERIOR/NORTHERN NEW ENGLAND SNOWS  
TO END THE EXTENDED HOLIDAY WEEKEND.  
 
UPSTREAM, RECENT GFS RUNS HAVE BEEN GENERALLY MORE PROGRESSIVE  
THAN THE ECMWF AND UKMET/CANADIAN WITH THE UPPER TROUGH AND  
SURFACE LOW/FRONT MOVING OUT OF THE MID-MISSISSIPPI VALLEY SUNDAY.  
MULTI-DAY TRENDS SUPPORT SLIGHTLY SLOWER THAN COMPOSITE SOLUTION,  
ESPECIALLY WITH TIME. FLOW PROGRESSION SHOULD SLOW NEXT WEEK AS  
STRONG UPPER RIDGING ASSERTS ITSELF OVER NORTHEASTERN CANADA TO  
BLOCK THE FLOW OUT TO THE NORTHEAST. BY NEXT WED-THU, THE EASTERN  
SYSTEM WILL SLOWLY EXIT TO THE EAST AS THE UPPER LOW GETS TRAPPED  
OVER ONTARIO AND THEN REINFORCED FROM CENTRAL CANADA. THIS COULD  
PRODUCE SOME HIGHER ELEVATION SNOW AND PERHAPS A SOMEWHAT  
LOCALIZED HEAVY RAIN EVENT FOR SOUTHERN MAINE.  
 
IN THE WEST, RENEWED TROUGHING WILL ATTEMPT TO PUSH INLAND INTO  
THE BRIEFLY RE-ESTABLISHED RIDGE EARLY NEXT WEEK, BUT MAY TAKE  
ANOTHER PUSH OF UPPER TROUGHING TO FINALLY KNOCK IT DOWN BY  
WEDNESDAY AND THURSDAY PER THE ENSEMBLES. THE ECMWF STILL SEEMS  
TOO AGGRESSIVE TO LOWER HEIGHTS WHILE ITS ENSEMBLE MEAN SEEMED  
MORE REASONABLE, THOUGH CERTAINLY QUICKER THAN THE GFS/GEFS MEAN  
THAT HAS BEEN MORE INCONSISTENT WITH UPSTREAM PACIFIC SYSTEM  
DEVELOPMENTS OVER THE PAST FEW DAYS. PREFER A COMPOSITE THAT WOULD  
NOW DELAY RIDGE WEAKENING A BIT MORE THAN WPC CONTINUITY. THERE IS  
STILL QUITE A BIT OF FORECAST SPREAD, BUT RIDGES OFTEN FIND A WAY  
TO REMAIN LONGER THAN ORIGINALLY FORECAST.  
 
SCHICHTEL  
 
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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