347  
FXUS02 KWBC 220651  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
151 AM EST THU NOV 22 2018  
 
VALID 12Z SUN NOV 25 2018 - 12Z THU NOV 29 2018  
   
..OVERVIEW
 
 
ACTIVE PATTERN FOR THE NORTHERN CORNERS OF THE LOWER 48 NEXT WEEK  
AS TROUGHING SETTLES INTO THE EASTERN GREAT LAKES AND ANOTHER  
PACIFIC SYSTEM OR TWO PUSHES INTO WA/OR AND EVENTUALLY NORTHERN  
CALIFORNIA. COLDER THAN AVERAGE TEMPERATURES ARE LIKELY FOR THE  
CENTRAL STATES EASTWARD BUT CLOSER TO AVERAGE IN THE WEST. LEAD  
SYSTEM AT THE START OF THE MEDIUM RANGE ON SUNDAY WILL PROVIDE  
SOME WINTRY WEATHER ON ITS NORTH SIDE FROM IOWA INTO WISCONSIN  
THAT WILL LIFT INTO THE NORTHEAST EARLY NEXT WEEK.  
 
   
..GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
THE 18Z GFS/GEFS AND 12Z ECMWF/ECMWF ENSEMBLE MEAN AND FV3-GFS  
PROVIDED A GOOD STARTING POINT TO THE FORECAST FOR THE SUN-TUE  
PERIOD, BUT WITH LINGERING DIFFERENCES IN THE EAST. THE GFS/GEFS  
WERE GENERALLY A BIT QUICKER THAN THE ECMWF/ECMWF ENSEMBLE MEAN  
(AND 12Z UKMET/CANADIAN) WITH THE UPPER TROUGH AND SURFACE  
LOW/FRONT MOVING OUT OF THE MID-MISSISSIPPI VALLEY SUNDAY BUT  
MULTI-DAY TRENDS STILL SUPPORT A MIDDLE SOLUTION OR JUST SLOWER  
THAN DOWN THE MIDDLE GIVEN THE PROGRESSIVE PATTERN STILL IN PLACE.  
THAT CHANGES AFTER SUNDAY AS STRONG UPPER RIDGING ASSERTS ITSELF  
OVER NORTHEASTERN CANADA TO BLOCK THE FLOW OUT TO THE NORTHEAST.  
IN ADDITION, ANOTHER 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.  
 
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, TROUGHING WILL ATTEMPT TO PUSH INTO THE BRIEFLY  
RE-ESTABLISHED RIDGE ON SUNDAY INTO MONDAY BUT MAY TAKE ANOTHER  
PUSH OF UPPER TROUGHING TO FINALLY KNOCK IT DOWN BY WEDNESDAY AND  
THURSDAY PER THE ENSEMBLES. THE 12Z ECMWF SEEMED TOO AGGRESSIVE TO  
LOWER HEIGHTS WHILE ITS ENSEMBLE MEAN SEEMED MORE REASONABLE,  
THOUGH QUICKER THAN THE GEFS MEAN. SPLIT THE DIFFERENCE SINCE  
ALTHOUGH THE TREND HAS BEEN TO WEAKEN THE RIDGE A BIT QUICKER THEY  
SOMETIMES FIND A WAY TO REMAIN LONGER THAN ORIGINALLY FORECAST.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
SUNDAY WILL SEE ONE SYSTEM OFF THE NY BIGHT WITH A POTENTIALLY  
SHORT-LIVED BUT IMPACTFUL PRECIPITATION EVENT - COASTAL RAIN BUT  
ELEVATION/INLAND SNOW FOR SOUTHERN/SOUTHEASTERN NEW ENGLAND INTO  
MAINE. OVER MISSOURI, ORGANIZING LOW PRESSURE WILL LIFT TOWARD  
LAKE ERIE BY MONDAY WITH RAIN ALONG/AHEAD OF THE FRONT BUT SNOW TO  
ITS NORTH -- PERHAPS SEVERAL INCHES FROM IOWA EAST-NORTHEASTWARD.  
TRIPLE POINT LOW SHOULD WRAP ACROSS SOUTHEASTERN NEW ENGLAND AND  
INTO THE GULF OF MAINE BY TUESDAY BEFORE SLOWLY HEADING EASTWARD.  
NEXT TUE-THU WILL BE ACTIVE IN THE PAC NW WITH LOW ELEVATION RAIN  
AND HIGHER ELEVATION SNOW AS A LEAD AND SECONDARY SYSTEM COME  
ASHORE. PRECIPITATION WILL WORK ITS WAY SOUTHWARD THROUGH NORTHERN  
CALIFORNIA BY NEXT THURSDAY.  
 
TEMPERATURES WILL GENERALLY BE BELOW AVERAGE OVER MOST OF THE  
LOWER 48 BY ABOUT 5-10F. A COUPLE BRIEF EXCEPTIONS WOULD BE JUST  
EAST OF THE MISSISSIPPI ON SUNDAY AHEAD OF THE COLD FRONT AND ALSO  
SOUTHERN FLORIDA UNTIL ABOUT TUESDAY WHEN A COLD FRONT SHOULD  
SETTLE INTO THE FLORIDA STRAITS.  
 
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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