404  
FXUS02 KWBC 190659  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
158 AM EST FRI NOV 19 2021  
 
VALID 12Z MON NOV 22 2021 - 12Z FRI NOV 26 2021  
 
...POTENTIAL CONTINUES FOR A SIGNIFICANT STORM TO AFFECT THE EAST  
NEXT WEEK WITH POSSIBLE MODERATE TO HEAVY RAINFALL ACROSS PORTIONS  
OF THE SOUTHERN PLAINS/LOWER MISSISSIPPI VALLEY AROUND OR ON  
THANKSGIVING DAY...  
   
..OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
AMPLIFICATION OF AN EASTERN U.S. UPPER TROUGH WILL BE UNDERWAY AS  
THE MEDIUM RANGE PERIOD STARTS MONDAY, PUSHING A COLD FRONT OFF  
THE EAST COAST BY TUESDAY AS LOW PRESSURE THEN LINGERS NEAR/OFF  
THE CANADIAN MARITIMES THE REMAINDER OF THE WEEK. OUT WEST, A  
SOUTHERN STREAM UPPER LOW INITIALLY SOUTHWEST OF CALIFORNIA SHOULD  
COMBINE WITH A PACIFIC SHORTWAVE TO YIELD AMPLIFIED TROUGHING, AND  
POTENTIALLY EMBEDDED COMPACT CLOSED LOW, TO DROP SOUTHWARD ALONG  
THE CALIFORNIA COAST AND INTO NORTHERN MEXICO BY THE END OF THE  
WEEK. NORTHERN STREAM ENERGY MAY DEEPEN AS IT TRACKS NEAR THE  
U.S./CANADIAN BORDER AND INTO THE GREAT LAKES BY FRIDAY.  
 
MODELS AND ENSEMBLES SHOW REASONABLE AGREEMENT ON THE EVOLUTION OF  
THE EAST COAST TROUGH/CLOSED LOW BUT CONTINUE TO EXHIBIT SOME  
SMALLER SCALE DIFFERENCES IN INTENSITY AND LOCATION OF SURFACE LOW  
PRESSURE LINGERING NEAR THE CANADIAN MARITIMES LATER IN THE WEEK.  
12Z (YESTERDAY) CMC IS DISPLACED A BIT WEST OF THE LATEST ECMWF  
AND GFS RUNS, WHICH ALSO HAVE SUPPORT FROM THE ENSEMBLE MEANS.  
 
OUT WEST, THE LATEST GUIDANCE HAS TRENDED DEEPER/STRONGER WITH  
PACIFIC NORTHWEST ENERGY WHICH MAY FORM A CLOSED LOW DROPPING  
SOUTHWARD ALONG THE CALIFORNIA COAST AND INTO THE NORTHERN MEXICO  
DURING THE EARLY TO MIDDLE PART OF NEXT WEEK. BY THURSDAY THOUGH,  
RUN TO RUN VARIABILITY INCREASES SIGNIFICANTLY REGARDING THE  
EVOLUTION AND OF THIS SOUTHERN STREAM ENERGY ACROSS NORTHERN  
MEXICO AND POTENTIALLY INTO PARTS OF THE HIGH PLAINS. THE LATEST  
RUN OF THE ECMWF IS THE DEEPEST/SLOWEST PIECE OF GUIDANCE, WHILE  
THE GFS IS WEAKER AND A LITTLE MORE PROGRESSIVE. ENSEMBLE  
SOLUTIONS VARY WIDELY BUT SUGGEST THAT BOTH THE ECMWF AND GFS ARE  
WITHIN THE REALM OF POSSIBILITIES. THE ENSEMBLE MEANS RIGHT NOW  
SEEM TO BE THE BEST STARTING POINT, WITH A MORE MIDDLE GROUND  
SOLUTION.  
 
THE OVERNIGHT MEDIUM RANGE PROGS USED A DETERMINISTIC MODEL BLEND  
FOR DAYS 3-5 (WITH SLIGHTLY MORE WEIGHTING TOWARDS THE ECMWF AND  
GFS). AFTER THIS, THE FORECAST TRENDED QUICKLY TOWARDS THE  
ENSEMBLE MEANS, WITH SOME MODEST CONTRIBUTIONS STILL FROM THE  
DETERMINISTIC SOLUTIONS FOR ADDED SYSTEM DEFINITION. OVERALL, THIS  
LEFT A REASONABLY CONSISTENT STARTING POINT WITH THE PREVIOUS WPC  
FORECAST.  
 
   
..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 NORTHEAST 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 1O-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. ESPECIALLY  
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.  
 
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 LATE WEEK, WITH TEMPERATURES  
GENERALLY NEAR OR SLIGHTLY ABOVE AVERAGE ACROSS THE WEST UPPER  
LEVEL RIDGING ATTEMPS TO BUILD OVER THE REGION.  
 
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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