801  
FXUS02 KWBC 302023  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
322 PM EST THU DEC 30 2021  
 
VALID 12Z SUN JAN 02 2022 - 12Z THU JAN 06 2022  
 
...HEAVY RAIN THREAT FOR THE SOUTHEAST/MID-ATLANTIC SUNDAY ALONG  
WITH SNOW/ICE POTENTIAL FROM THE SOUTHERN APPALACHIANS TO THE  
NORTHEAST...  
...COASTAL HEAVY RAIN AND MOUNTAIN FOCUSING HEAVY SNOW THREAT  
SUNDAY-THURSDAY FOR THE NORTHWEST/NORTHERN CALIFORNIA SPREADS TO  
THE NORTHERN GREAT BASIN/ROCKIES...  
...ANOTHER ARCTIC BLAST FOR THE NORTH-CENTRAL U.S.  
TUESDAY-THURSDAY WITH LEAD LOW SNOWS INTO THE GREAT LAKES AND  
INTERIOR NORTHEAST...  
 
...GUIDANCE/PREDICTABILITY ASSESSMENT AND WEATHER/HAZARDS  
HIGHLIGHTS...  
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM A  
COMPOSITE OF REASONABLY WELL CLUSTERED GUIDANCE FROM THE 06 UTC  
GFS AND 00 UTC ECMWF DAYS 3/4 (SUNDAY/MONDAY) ALONG WITH THE 13  
UTC NBM IN A PATTERN WITH OVERALL ABOVE NORMAL PREDICTABILITY.  
HOWEVER, THERE ARE LINGERING MODEL DIFFERENCES WITH THE  
TIMING/PHASING OF FRONTAL WAVES OVER THE SOUTHEAST/EAST AND  
SUBSEQUENT COASTAL LOW POTENTIAL IN THIS PERIOD. THIS COMPOSITE  
DEVELOPS A SURFACE SYSTEM SEEMINGLY MOST CONSISTENT WITH MEAN  
UPPER TROUGH EJECTION, ALBEIT WITH LESS STREAM SEPARATION ALOFT  
THAN THE 00 UTC CANADIAN/UKMET AND 12 UTC CANADIAN. WPC PROGS  
DEVELOP A BETTER DEFINED INLAND SYSTEM/COASTAL LOW THAN CONTINUITY  
THAT ACTS TO HOLD PRECIPITATION BACK INTO THE MID-ATLANTIC. A 12  
UTC GFS/ECMWF/UKMET COMPOSITE IS IN LINE WITH THAT SOLUTION.  
EXPECT RECORD BREAKING WARMTH TO LINGER INTO SUNDAY IN ADVANCE OF  
THE STARKLY TEMPERATURE CONTRASTING FRONT OVER THE SOUTHEAST/EAST.  
 
THE MAIN WEATHER FOCUS INTO NEXT WEEK TURNS TO ANOTHER ARCTIC  
OUTBREAK DOWN THROUGH THE NORTH-CENTRAL U.S. WITH LEAD LOW SNOWS  
AND MODEST TRAILING FRONT RAINS OVER THE EAST-CENTRAL STATES. THE  
PATTERN WILL ALSO FEATURE UPSTREAM A MULTI-DAY PRECIPITATION  
EPISODE FOR THE NORTHWEST AND CALIFORNIA WITH THE THREAT OF  
COASTAL HEAVY RAINS AND INLAND/MOUNTAIN SNOWS, WITH THE SNOW  
THREAT SPREADING INTO THE NORTHERN GREAT BASIN/ROCKIES WITH  
DYNAMIC/AMPLIFYING PACIFIC SYSTEM ENERGIES/HEIGHT FALLS AND MODEST  
MOISTURE INFLUX SURGES OVER THE PACIFIC. MODEL DIFFERENCES,  
ESPECIALLY AT THE SURFACE BECOME INCREASINGLY PROBLEMATIC  
TUESDAY-THURSDAY DESPITE A GENERALLY COMPATIBLE LARGER SCALE  
PATTERN EVOLUTION ALOFT. THE WPC MEDIUM RANGE PRODUCT SUITE IN  
THIS PERIOD WAS INSTEAD MAINLY DERIVED FROM A COMPOSITE OF  
REASONABLY WELL CLUSTERED GUIDANCE FROM THE 06 UTC GEFS MEAN AND  
00 UTC ECMWF ENSEMBLE MEAN THAT FORGED A SOLUTION NEAR THE MIDDLE  
OF THE FULL ENVELOPE OF MODEL SOLUTIONS. THE MAIN GUIDANCE TREND  
WAS TO LIMIT THE SOUTHWARD EXTENT OF HEIGHT FALLS AND HEAVY  
PRECIPITATION DOWN INTO CALIFORNIA COMPARED TO EARLIER RUNS AND  
THAT SEEMS REASONABLE CONSIDERING UPSTREAM OMEGA BLOCK ORIENTATION  
OVER THE NORTHEAST PACIFIC.  
 
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 PRECIPITATION ACROSS PORTIONS OF CALIFORNIA, THE GREAT  
BASIN, AND THE PACIFIC NORTHWEST,  
SUN-THU, JAN 2-JAN 6.  
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN/CENTRAL PLAINS, THE  
GREAT BASIN, THE NORTHERN/CENTRAL  
ROCKIES, AND THE PACIFIC NORTHWEST, MON-WED, JAN 3-JAN 5.  
- HEAVY SNOW ACROSS PORTIONS OF THE GREAT LAKES AND THE UPPER  
MISSISSIPPI VALLEY, WED, JAN 5.  
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHEAST, SUN, JAN 2.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL APPALACHIANS,  
THE OHIO VALLEY, AND THE TENNESSEE  
VALLEY.  
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE PLAINS,  
AND THE MISSISSIPPI VALLEY, SUN,  
JAN 2.  
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE  
NORTHERN/CENTRAL PLAINS, THE UPPER/MIDDLE  
MISSISSIPPI VALLEY, AND THE NORTHERN ROCKIES, WED-THU, JAN 5-JAN 6.  
- HEAVY PRECIPITATION ACROSS PORTIONS OF THE ALASKA PANHANDLE,  
SUN, JAN 2.  
 
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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