278  
FXUS02 KWBC 191919  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
219 PM EST FRI NOV 19 2021  
 
VALID 12Z MON NOV 22 2021 - 12Z FRI NOV 26 2021  
 
...DEPARTING EAST COAST SYSTEM TO PRODUCE HEAVY RAINFALL IN  
EASTERN MAINE MONDAY NIGHT AND ANOMALOUSLY COLD TEMPERATURES IN  
THE SOUTHEAST THROUGH EARLY NEXT WEEK...  
 
...INCREASING CONFIDENCE IN THANKSGIVING/BLACK FRIDAY HEAVY  
RAINFALL EVENT FOR PORTIONS OF THE SOUTHERN PLAINS AND LOWER  
MISSISSIPPI VALLEY...  
   
..OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
AN AMPLIFYING TROUGH IN THE EASTERN U.S. WILL SEE OUT A PAIR OF  
COASTAL SURFACE LOW PRESSURE SYSTEMS INTO THE CANADIAN MARITIME AT  
THE BEGINNING OF OUR MEDIUM RANGE PERIOD (MONDAY AND TUESDAY).  
UPPER-LEVEL RIDGING WILL SHIFT INTO THE CENTRAL U.S. BEFORE A  
NORTHERN PACIFIC TROUGH PHASES WITH A CUT-OFF LOW WEST OF THE  
CALIFORNIA COAST, AND AMPLIFIES OVER THE SOUTHWEST ON TUESDAY. THE  
NEW TROUGH MAY SPLIT BACK INTO SEPARATE STREAMS HEADING INTO  
MIDWEEK AS THE SOUTHERN ENERGY DIGS INTO MEXICO AND THE NORTHERN  
WAVE RIDES THE UPPER JET ACROSS THE NORTHERN/CENTRAL TIER OF THE  
COUNTRY.  
 
THE LATEST GUIDANCE IS IN AGREEMENT WITH THE TIMING OF A DEPARTING  
UPPER-LEVEL TROUGH IN THE EAST ON MONDAY-TUESDAY. SOME RUN-TO-RUN  
VARIABILITY EXISTS BETWEEN GFS MEMBERS AS THEY STRUGGLE WITH  
DECIDING WHETHER TO GENERATE A CLOSED UPPER-LOW OR NOT. THE 00Z  
CMC ATTEMPTS TO RETROGRADE A PAIR OF CLOSED UPPER-LOWS OVER THE  
NORTHEAST BY THANKSGIVING, WHICH IS OUT OF STEP WITH THE OTHER  
DETERMINISTICS. THE ENSEMBLE MEANS, SAVE FOR THE CANADIAN, HANDLE  
THE TIMING AND INTENSITY OF THE DEPARTING SYSTEM FAIRLY WELL.  
UNFORTUNATELY, THIS DOESN'T TRANSLATE WELL TO THE SURFACE FOR THE  
GFS AS ITS 06Z RUN ATTEMPTS TO DRAG THE SURFACE LOW BACK TOWARD  
THE NEW ENGLAND COAST BY THURSDAY WHILE THE 00Z RUN KEEPS IT OUT  
TO SEA WITH THE REST OF THE MODELS.  
 
MODELS HAVE TRENDED STRONGER WITH THE PACIFIC ENERGY APPROACHING  
THE WEST COAST ON MONDAY. WE BEGIN TO GET MORE PRONOUNCED SPREAD  
BY WEDNESDAY AS DETERMINISTICS LIKE THE 06Z GFS AND 00Z UKMET  
BEGIN TO DEVIATE FROM THE ENEMBLE MEANS BY SLOWING AND  
STRENGTHENING THE UPPER-LOW. ALL OF THE OPERATIONAL MODELS HAVE  
TRENDED TOWARD A DEEPENING CLOSED LOW FEATURE OVER NORTHERN MEXICO  
BY THANKSGIVING DAY. THAT BEING SAID, THE ENSEMBLE MEANS APPEAR TO  
BE OUR BEST BET FOR DETERMINING THE 500MB PATTERN OVER THE  
SOUTHWEST AND GREAT PLAINS TOWARD THE TAIL END OF THE MEDIUM RANGE  
PERIOD.  
 
MEDIUM RANGE PROGS USED A GENERAL DETERMINISTIC MODEL BLEND WITH  
HEAVIER WEIGHTING TOWARD THE 06Z GFS AND 00Z UKMET ON DAYS 3 AND  
4. BY DAY 5 THE 06Z GFS WEIGHTING WAS REDUCED IN FAVOR OF ITS 00Z  
PREDECESSOR DUE TO THE 06Z'S TROUBLE RESOLVING THE ATLANTIC LOW,  
AND ENSEMBLE MEANS WERE ADDED TO THE BLEND. THIS BLEND RATIO  
CONTINUES THROUGH DAYS 6 & 7.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
THE NORTHEAST LOW PRESSURE WILL BRING A COLD FRONT INTO AND  
THROUGH THE EAST ON MONDAY WITH MUCH OF THE HEAVIEST PRECIPITATION  
HEADING OFF THE EAST COAST. MODERATE TO HEAVY RAINFALL SHOULD  
CONTINUE INTO PARTS OF NEW ENGLAND THOUGH WITH THE HEAVIEST TOTALS  
(IN EXCESS OF AN INCH) ACROSS FAR EASTERN MAINE ON MONDAY AIDED BY  
STRONG ATLANTIC INFLOW. COLD AIR FILTERING IN BEHIND THE SYSTEM  
SHOULD SUPPORT AT LEAST LIGHT ACCUMULATING SNOW DOWNWIND OF THE  
LOWER GREAT LAKES AS WELL AS ALONG WESTWARD-FACING TERRAIN FROM  
THE CENTRAL APPALACHIANS AND NORTHEASTWARD. THERE IS STILL ENOUGH  
UNCERTAINTY IN SYSTEM EVOLUTION TO ALLOW FOR OTHER POSSIBILITIES  
REGARDING PRECIPITATION TYPE AND AMOUNTS, EVEN INTO PARTS OF FAR  
NORTHERN NEW ENGLAND. DEEPENING LOW PRESSURE SHOULD ALLOW FOR A  
PERIOD OF BREEZY/GUSTY WINDS ACROSS MUCH OF THE EAST MONDAY AND  
TUESDAY AND POSSIBLY INTO THE MIDDLE AND LATTER PARTS OF THE WEEK  
ACROSS THE NORTHEAST AS LOW PRESSURE LINGERS OFFSHORE. DAYTIME  
HIGHS AND MORNING LOWS MONDAY AND TUESDAY COULD BE 10-20 DEGREES  
BELOW NORMAL FROM PORTIONS OF THE OHIO VALLEY/MIDWEST INTO THE  
MID-ATLANTIC AND THE SOUTHEAST. NEAR TO BELOW FREEZING MORNING  
LOWS COULD EXTEND RATHER FAR INTO PARTS OF THE SOUTH WHICH MAY  
IMPACT SENSITIVE SOILS. FOR NORTHERN LOCATIONS, THIS COMBINATION  
OF COLD TEMPERATURES AND GUSTY WINDS COULD MAKE FOR SOME  
UNPLEASANT WIND CHILLS DURING THE UPCOMING HOLIDAY WEEK.  
 
THE PACIFIC NORTHWEST INTO NORTHERN ROCKIES SHOULD SEE MOSTLY  
LIGHT TO PERHAPS LOCALLY MODERATE PRECIPITATION DURING THE FIRST  
HALF OF NEXT WEEK WITH A SHORTWAVE/COLD FRONT ARRIVING FROM THE  
PACIFIC. THE COMBINATION OF THIS ENERGY ALOFT AND THE  
OPENING/PROGRESSION OF THE UPPER LOW SOUTHWEST OF CALIFORNIA MAY  
SPREAD SOME MOISTURE INTO OTHER PARTS OF THE WEST BY  
TUESDAY/WEDNESDAY, BUT STILL WITH MODEST CONFIDENCE FOR  
PRECIPITATION COVERAGE/AMOUNTS. BY MID WEEK, THE WESTERN FRONT  
SHOULD REACH FAR ENOUGH INTO THE PLAINS TO BEGIN INTERACTING WITH  
GULF MOISTURE TO PRODUCE AN EXPANDING AREA OF MODERATE TO POSSIBLY  
HEAVY RAINFALL FROM EASTERN TEXAS INTO PARTS OF THE LOWER  
MISSISSIPPI VALLEY FOR WEDNESDAY AND ESPECIALLY INTO THANKSGIVING  
DAY, BEFORE SHIFTING FOCUS TO THE CENTRAL GULF COAST.  
 
ABOVE NORMAL TEMPERATURES AHEAD OF THE WESTERN FRONT WILL MARCH  
FROM THE ROCKIES TO THE PLAINS MONDAY-WEDNESDAY WITH ANOMALIES +10  
TO +15F POSSIBLE. MODESTLY ABOVE NORMAL TEMPERATURES ARE POSSIBLE  
INTO THE SOUTHERN PLAINS AND MIDWEST ON THURSDAY, WITH  
TEMPERATURES GENERALLY NEAR OR SLIGHTLY ABOVE AVERAGE ACROSS THE  
WEST UPPER LEVEL RIDGING ATTEMPS TO BUILD OVER THE REGION.  
TEMPERATURES WILL DROP AGAIN FOR THIS REGION BY FRIDAY AS THE COLD  
FRONT ASSOCIATED WITH THE LOW PRESSURE SYSTEM PROPAGATES THROUGH.  
 
KEBEDE/SANTORELLI  
 
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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