290  
FXUS02 KWBC 261202  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
701 AM EST FRI NOV 26 2021  
 
VALID 12Z MON NOV 29 2021 - 12Z FRI DEC 03 2021  
   
..OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MULTIPLE SHORTWAVES WILL TRACK ACROSS THE CONUS DURING THE  
EXTENDED PERIOD; WHICH WILL REINFORCE THE MEAN TROUGH OVER THE  
EASTERN U.S. OVER THE WEST, AN AMPLIFIED RIDGE WILL BEGIN TO  
WEAKEN AS A COUPLE OF SHORTWAVES MOVE THROUGH AND INTO THE CENTRAL  
U.S., WHICH MAY ALSO HELP TO FLATTEN THE OVERALL UPPER PATTERN  
SOME BY MID TO LATER NEXT WEEK.  
 
GENERALLY SPEAKING, THE GLOBAL GUIDANCE AND THE ENSEMBLE MEANS  
HAVE A FAIR HANDLE ON THE EVOLUTION OF THIS PATTERN ALBEIT WITH  
UNCERTAINTY IN THE SPECIFIC DETAILS. THE IMPULSES MOVING ACROSS  
THE NORTHERN U.S. AND GREAT LAKES REGIONS POSE TIMING AND  
MAGNITUDE DIFFERENCES THAT ESSENTIALLY WOULD AFFECT A SURFACE LOW  
DEEPENING OFF THE NORTHEAST COAST. THE GUIDANCE IS FAVORING AN  
EASTERN SHIFT AS THE SURFACE LOW SKIRTS NEAR THE NEW ENGLAND  
COAST. ONCE AGAIN THE UKMET IS POSITIONED NOTABLY SOUTH OF THE  
REST OF THE CLUSTERED GUIDANCE AND WAS ALSO AS MUCH AS 10 MB  
DEEPER WITH THE LOW TRACKING ACROSS THE CANADIAN PRAIRIES/NORTHERN  
TIER U.S. THEREFORE WAS CONSIDERED AN OUTLIER FOR THIS ISSUANCE.  
AS NOTED IN THE PREVIOUS FORECAST, THE CMC WHICH SHOWED A STRONG  
SHORTWAVE MOVING INTO THE WEST DIVING SOUTH TO MEET UP WITH ENERGY  
OVER NORTHERN MEXICO TO CREATE A CLOSED LOW DIFFERENTLY THAN  
CONSENSUS. THE CMC WAS USABLE IN THE INITIAL PERIODS.  
 
THE WPC BLEND UTILIZED A COMBINATION OF THE 12/18Z GFS, ECWMF AND  
CMC AS A STARTING POINT THEN GRADUALLY CEASING USE OF THE CMC  
WHILE INCREASING THE INCLUSION OF THE GEFS AND ECWMF MEANS. THIS  
APPROACH HELPED MAINTAIN A DEGREE OF CONTINUITY AS WELL AS  
MINIMIZING INDIVIDUAL MODEL DIFFERENCES.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
REMNANT MOISTURE FROM THE WEAKENING ATMOSPHERIC RIVER WILL KEEP  
LINGERING MODERATE TO LOCALLY HEAVY RAINFALL POSSIBLE FOR THE  
OLYMPIC PENINSULA, FAR NORTHERN CASCADES AND THE SURROUNDING  
AREAS. RELATIVELY LIGHT PRECIPITATION IS LIKELY TO CONTINUE FOR  
THIS REGION THROUGH MONDAY BEFORE ANOTHER INCREASE IN MOISTURE  
BRINGS ANOTHER ROUND OF MODERATE TO LOCALLY HEAVY PRECIPITATION TO  
WESTERN WASHINGTON AROUND TUESDAY-WEDNESDAY, WHICH MAY BE MOSTLY  
RAIN BUT WITH SOME UNCERTAINTY IN SNOW LEVELS AT THIS POINT.  
PORTIONS OF THE NORTHERN ROCKIES IS ALSO EXPECTED TO HAVE LIGHT  
PRECIPITATION WITH THIS FLOW.  
 
PERIODIC LAKE EFFECT SNOW/ENHANCED SNOWFALL IS EXPECTED FOR THE  
GREAT LAKES REGIONS THROUGH THE EXTENDED PERIOD AS NORTHWESTERLY  
FLOW PASSES ACROSS THE OPEN LAKES. A FAVORED LOCATIONS DOWNWIND OF  
LAKE ERIE WILL LIKELY OBSERVE ENHANCEMENTS THROUGH MONDAY WHILE  
AREAS DOWNWIND OF LAKE ONTARIO ARE ANTICIPATED LATER IN THE WEEK.  
IN ADDITION TO THE LAKE EFFECT SNOWS, PARTS OF THE MIDWEST AND THE  
NORTHEAST WILL HAVE LIGHT PRECIPITATION AS ENERGY PASSES ALOFT.  
MODELS HAVE BEEN TRENDING DOWN FOR THE QPF AMOUNTS OVER NEW  
ENGLAND THAT PAST FEW RUNS. ALTHOUGH THERE ARE DIFFERENCES IN THE  
LOCATION OF THE ATLANTIC LOW, THE POSSIBILITY OF FLOW WRAPPING  
INTO THE LOW ONSHORE COULD YIELD LIGHT RAIN OR SNOWFALL. OTHER  
THAN THE TWO HIGHLIGHTED REGIONS, A MAJORITY OF THE COUNTRY WILL  
BE GENERALLY DRY OTHER THAN SOME EARLY WEEK SHOWERS FOR FLORIDA  
AND INCREASING MOISTURE FOR TEXAS MIDWEEK ONWARD.  
 
TEMPERATURES WILL GENERALLY BE SLIGHTLY BELOW NORMAL ACROSS THE  
EASTERN U.S. AS THE MEAN TROUGH BECOMES REINFORCED, WITH SOME  
MODERATION BACK TOWARDS NORMAL WEDNESDAY AND THURSDAY. MUCH OF THE  
WEST AND CENTRAL STATES WILL MAINTAIN WARMTH THROUGH THE EXTENDED  
FORECAST THANKS TO THE RIDGING OVER THE REGION. A FEW LOCATIONS  
MAY REACH OR EXCEED DAILY MAXIMUM AND MINIMUM TEMPERATURE RECORDS,  
WHERE SOME PLACES COULD REGISTER 20 TO 30 DEGREES ABOVE SEASONAL  
AVERAGE. AS THE FLOW FLATTENS DURING THE LATE PERIOD, ABOVE NORMAL  
TEMPERATURES SHOULD ALSO BEGIN EXPANDING INTO THE MIDWEST AND  
SOUTH.  
 
CAMPBELL  
 
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDICES ARE 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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