667  
FXUS02 KWBC 151842  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
142 PM EST MON NOV 15 2021  
 
VALID 12Z THU NOV 18 2021 - 12Z MON NOV 22 2021  
   
..OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
GUIDANCE GENERALLY AGREES THAT PROGRESSIVE MEAN FLOW LATE THIS  
WEEK SHOULD EVENTUALLY TRANSITION TOWARD AN AMPLIFYING MEAN TROUGH  
OVER THE CENTRAL-EASTERN U.S. AS A RIDGE BUILDING OVER THE EASTERN  
PACIFIC DURING THE WEEKEND BEGINS TO MOVE INTO THE WEST EARLY NEXT  
WEEK. THIS EVOLUTION SHOULD PROMOTE A COUPLE SURGES OF CHILLY AIR  
OVER THE CENTRAL/EASTERN STATES WHILE TEMPERATURES OVER THE WEST  
REMAIN NEAR TO ABOVE NORMAL.  
 
THE MODELS AND GUIDANCE SHOW FAIRLY GOOD AGREEMENT ON THE LARGE  
SCALE EVOLUTION DURING THE MEDIUM RANGE PERIOD, BUT CONTINUE TO  
OFFER PLENTY OF VARIABILITY IN THE DETAILS. MODELS HAVE TRENDED A  
LITTLE WEAKER WITH A STORM EXPECTED TO TRACK TOWARDS THE PACIFIC  
NORTHWEST LATE THIS WEEK, WITH THE UKMET THE WEAKEST AND QUICKEST  
TO EJECT THAT ENERGY INTO SOUTHWEST CANADA/FAR NORTHERN U.S..  
AFTER DAY 4, UNCERTANITY IN THE EVOLUTION OF THE SHORTWAVE AS IT  
CROSSES INTO THE CENTRAL U.S. THIS WEEKEND AND EVENTUALLY  
AMPLIFIES OVER THE EAST EARLY NEXT WEEK IS HIGH AS SEVERAL PIECES  
OF ENERGY ROTATE THROUGH THE TROUGH TO HELP AMPLIFY AND REINFORCE  
THE TROUGHING AS IT ENTERS THE EAST NEXT MONDAY. THIS TEMPERS  
CONFIDENCE IN THE DETAILS OF THE GENERAL AREA OF LOWER PRESSURE  
AND ONE OR MORE FRONTS CROSSING THE CENTRAL INTO EASTERN U.S. THIS  
WEEKEND. THERE IS ENOUGH ENSEMBLE SUPPORT TO MENTION POTENTIAL  
DEVELOPMENT OF A DEEP CYCLONE TO IMPACT PARTS OF THE NORTHEAST OR  
NEW ENGLAND EARLY NEXT WEEK/JUST BEYOND THE MEDIUM RANGE PERIOD.  
HOWEVER, THE MODEL SPREAD FOR TIMING AND INTENSITY OF THIS FEATURE  
REMAINS TOO HIGH TO BE ABLE TO TALK ABOUT SPECIFIC IMPACTS THIS  
MAY (OR MAY NOT) HAVE ON THE BUSY THANKSGIVING HOLIDAY TRAVEL  
WEEK.  
 
THE WPC FORECAST USED A GENERAL MODEL BLEND OF THE 06Z GFS WITH  
THE 00Z ECMWF AND CMC AS THE BASIS FOR THE FORECAST DAYS 3-4.  
AFTER THIS, ADDED AND GRADUALLY INCREASED CONTRIBUTIONS FROM THE  
ENSEMBLE MEANS TO HELP MITIGATE SOME OF THE HARDER TO RESOLVE  
DETAIL DIFFERENCES. THIS ALSO MAINTAINS DECENT CONTINUITY WITH THE  
PREVIOUS WPC FORECAST.  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
STRONG LOW PRESSURE TRACKING OVER EASTERN CANADA SHOULD BRING  
BRISK WINDS TO AREAS FROM THE UPPER MIDWEST INTO THE NORTHEAST  
THURSDAY-FRIDAY WHILE LIGHT TO MODERATE PRECIPITATION (MOSTLY  
RAIN) WILL ACCOMPANY THE TRAILING FRONT CROSSING THE EASTERN U.S..  
NORTHERN AND EASTERN PORTIONS OF THE GREAT LAKES SHOULD SEE A  
PERIOD OF LAKE EFFECT PRECIPITATION AFTER THE FRONTAL PASSAGE.  
MEANWHILE THE SOUTHERN FLORIDA PENINSULA MAY EXPERIENCE LOCALLY  
MODERATE TO HEAVY RAINFALL AROUND THURSDAY AS MOISTURE INTERACTS  
WITH A STALLED FRONT TO THE SOUTH AND ANOTHER FRONT APPROACHING  
FROM THE NORTHWEST. CONTINUED SPREAD AND VARIABILITY IN GUIDANCE  
FOR THE SYSTEM APPROACHING THE WEST COAST LATE THIS WEEK KEEP  
CONFIDENCE LOWER THAN DESIRED FOR THE SPECIFICS OF RAIN AND HIGHER  
ELEVATION SNOW THAT SHOULD SPREAD ACROSS THE CENTRAL/NORTHERN WEST  
COAST INTO THE NORTHERN ROCKIES. UPSTREAM MOISTURE MAY KEEP SOME  
PRECIPITATION OVER THE NORTHERN PACIFIC NORTHWEST THROUGH THE  
WEEKEND. AS SHORTWAVE ENERGY CONTINUES EASTWARD, EXPECT ANOTHER  
AREA OF RAIN TO DEVELOP FROM THE SOUTHERN PLAINS  
EASTWARD/NORTHEASTWARD FROM THE WEEKEND INTO EARLY NEXT WEEK AHEAD  
OF ONE OR MORE COLD FRONTS BUT AGAIN WITH LOW CONFIDENCE FOR  
COVERAGE AND AMOUNTS AT THIS TIME. PRECIPITATION COULD CHANGE TO  
SNOW OVER THE FARTHEST NORTH LATITUDES WITH REINFORCING COLD AIR.  
 
AREAS NEAR THE EAST COAST WILL SEE TEMPERATURES UP TO 10-15F ABOVE  
NORMAL ON THURSDAY AHEAD OF AN ADVANCING COLD FRONT. THE COOLING  
TREND BEHIND THIS FRONT WILL BRING GENERALLY 5-12F BELOW NORMAL  
READINGS FROM THE PLAINS INTO THE EAST THURSDAY-SATURDAY. UPSTREAM  
SYSTEM PROGRESSION MAY BRING A BRIEF EPISODE OF WARMTH FROM THE  
WEST INTO THE HIGH PLAINS LATE THIS WEEK, PEAKING WITH SOME HIGHS  
10-15F ABOVE NORMAL OVER THE CENTRAL HIGH PLAINS ON FRIDAY.  
ANOTHER PUSH OF COLD AIR SHOULD EXTEND SOUTHEASTWARD FROM THE  
NORTHERN PLAINS SUNDAY-MONDAY WITH HIGHS 5-10F BELOW NORMAL.  
 
SANTORELLI/RAUSCH  
 
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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