214  
FXUS02 KWBC 082023  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
323 PM EST MON NOV 08 2021  
 
VALID 12Z THU NOV 11 2021 - 12Z MON NOV 15 2021  
   
..ROBUST MIDWEST/GREAT LAKES LOW INTO LATER THIS WEEK
 
 
...MULTIPLE ROUNDS OF PRECIPITATION INTO THE PACIFIC NORTHWEST  
LATER THIS WEEK...  
 
   
..PATTERN OVERVIEW
 
 
UPPER RIDGING TO THE SOUTHWEST OF CALIFORNIA AS WELL AS OVER THE  
CANADIAN ARCHIPELAGO FAVORS AMPLIFIED TROUGHING OVER THE CENTRAL  
TO EASTERN CONUS LATER THIS WEEK INTO THE WEEKEND. THIS FAVORS A  
DEEPENING CENTRAL STATES CYCLONE THAT WILL LIFT NORTHEASTWARD  
THROUGH THE MIDWEST/GREAT LAKES INTO CANADA THU-SAT. MILDER AIR  
OVER MUCH OF THE LOWER 48 WILL TREND COOLER WITH TIME AS THE  
ATTENDANT COLD FRONT SWEEPS EASTWARD, FAVORING A WIDESPREAD SWATH  
OF MODEST TO LOCALLY HEAVY RAIN ACROSS MUCH OF THE EAST. WITHIN  
THE WESTERN HALF OF THE LOW PRESSURE AREA, WRAP-AROUND AND THEN  
LAKE EFFECT SNOW IS LIKELY OVER THE DAKOTAS/UPPER MIDWEST/GREAT  
LAKES LATE WEEK AND THEN THE CENTRAL/NORTHERN APPALACHIANS.  
 
UPSTREAM, THERE IS A GROWING GUIDANCE SIGNAL BRINGING A LONG FETCH  
PLUME OF PACIFIC MOISTURE INTO THE PACIFIC NORTHWEST, ESPECIALLY  
LATER THIS WEEK. FAVORABLE FLOW SHOULD FOCUS HEAVY RAINS AND  
ELEVATION SNOWS OVER THE OLYMPICS AND CASCADES.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
GUIDANCE CONTINUES TO ILLUSTRATE A REASONABLY SIMILAR LARGER SCALE  
PATTERN EVOLUTION AND FORECAST CLUSTERING HAS IMPROVED SLIGHTLY  
THU INTO FRI. A COMPOSITE BLEND OF THE GFS/ECMWF/CANADIAN/UKMET  
SEEMS REASONABLE, IS IN LINE WITH THE NBM AND GEFS/NAEFS/ECMWF  
ENSEMBLE MEANS AND MAINTAINS GOOD WPC CONTINUITY IN THIS TIME  
FRAME. HOWEVER, THE 00Z CANADIAN AND UKMET GUIDANCE BECOME FLATTER  
AND APPEAR TO RETROGRADE THE WESTERN RIDGE INTO THE PACIFIC, WHICH  
BY THE END OF THE PERIOD LEAVES THEM VERGING ON BEING COMPLETELY  
OUT OF PHASE WITH THE OTHER GUIDANCE. GIVEN UNCERTAINTY IN RECENT  
TRENDS, THE WPC PRODUCT SUITE WAS DERIVED FROM A COMPOSITE BLEND  
OF COMPATIBLE GUIDANCE FROM GFS/ECMWF/NAEFS/ECMWF  
ENSEMBLES/NATIONAL BLEND OF MODELS (WITH THE NBM REMOVED FROM QPF  
CONSIDERATION LATE IN THE PERIOD).  
 
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
AMPLIFYING UPPER PATTERN WILL SUPPORT SURFACE CYCLOGENESIS OVER  
THE UPPER MIDWEST INTO THU AS GULF MOISTURE STREAMS NORTHWARD  
ALONG AND AHEAD OF THE COLD FRONT, ENHANCING RAINFALL FROM THE  
SOUTHERN APPALACHIANS NORTHWARD INTO THE NORTHEAST. AS THE SYSTEM  
MOVES INTO CANADA, BACKSIDE COLD AIR FLOW BY NEXT FRIDAY WILL  
LIKELY SUPPORT SOME SNOW WITHIN THE SYSTEM'S COMMA HEAD OVER THE  
DAKOTAS/UPPER MIDWEST/GREAT LAKES AND SUBSEQUENTLY WITH COLD FLOW  
OFF THE LAKES AND INTO THE NORTHERN/CENTRAL APPALACHIANS. THIS  
COULD BE THE FIRST ACCUMULATING SNOW OF THE SEASON FOR SOME AREAS  
OF NORTHERN MINNESOTA INTO THE EASTERN DAKOTAS. TEMPERATURES WILL  
BE NEAR TO ABOVE NORMAL EARLY IN THE WEEK, WITH POSSIBLE RECORD  
HIGHS AHEAD OF THE FRONT ON FRIDAY IN THE MID-ATLANTIC, BUT  
TRENDING COOLER BY WEEK'S END ESPECIALLY INTO THE SOUTHEAST  
(RELATIVE TO TYPICAL MID-NOVEMBER VALUES THERE).  
 
UPSTREAM, THERE IS A GROWING GUIDANCE SIGNAL BRINGING SEVERAL  
ROUNDS OF RAIN AND MOUNTAIN SNOW TO THE PACIFIC NORTHWEST,  
ESPECIALLY LATER THIS WEEK. FAVORABLE FLOW SHOULD FOCUS HEAVY  
RAINS AND ELEVATION SNOWS OVER THE OLYMPICS AND WASHINGTON  
CASCADES.  
 
ROTH/SCHICHTEL  
 
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  
 
HAZARDS:  
- HEAVY RAIN ACROSS PORTIONS OF THE PACIFIC NORTHWEST, THU, NOV 11.  
- HEAVY SNOW ACROSS PORTIONS OF THE PACIFIC NORTHWEST AND THE  
NORTHERN GREAT BASIN, THU-FRI, NOV  
11-NOV 12.  
- HEAVY SNOW ACROSS PORTIONS OF THE PACIFIC NORTHWEST, THU, NOV 11.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHEAST.  
 
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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