853  
FXUS02 KWBC 300647  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
146 AM EST THU DEC 30 2021  
 
VALID 12Z SUN JAN 02 2022 - 12Z THU JAN 06 2022  
 
...NEW YEAR'S WEEKEND HEAVY RAIN/THUNDERSTORM THREAT FOR THE  
SOUTH/SOUTHEAST/MID-ATLANTIC AS A HEAVY SNOW THREAT SHIFTS FROM  
THE MIDWEST/GREAT LAKES/NORTHEAST DOWN THROUGH THE APPALACHIANS...  
 
...COASTAL HEAVY RAIN AND MOUNTAIN FOCUSING HEAVY SNOW THREAT  
SUNDAY-WEDNESDAY FROM THE NORTHWEST TO NORTH-CENTRAL CALIFORNIA...  
 
   
..GUIDANCE AND PREDICTABILITY ASSESSMENT
 
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS BASED OFF A COMPROMISE OF  
THE 12Z ECWMF/CMC/EC ENSEMBLE AND GEFS MEANS WITH INCLUSION OF THE  
NBM. THE CMC AND ECWMF HAVE BEEN CONSISTENT WITH THE OVERALL  
PATTERN CLUSTERING AND EVOLUTION THE PAST FEW DAYS WHILE THE GFS  
CONTINUES TO STRUGGLE. THE INCLUSION OF THE MEANS HELP TO REDUCE  
TIMING AND PHASING DIFFERENCES FOR THE MULTIPLE FEATURES DURING  
THE EXTENDED PERIOD. THIS MODEL BLEND HELPS TO MAINTAIN CONTINUITY.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
COASTAL RAINS AND MOUNTAIN SNOW IS EXPECTED ACROSS PARTS OF THE  
NORTHWEST AND CALIFORNIA AS AN AMPLIFIED UPPER TROUGH MOVES  
THROUGH THE WEST, THEN CROSSES THE ROCKIES SPREADING SNOW BEFORE  
ENTERING THE PLAINS. ONCE IN THE PLAINS THE EJECTED ENERGIES WILL  
HELP SPAWN SYSTEMS TO ENHANCE AN EMERGING CENTRAL TO EASTERN U.S.  
PRECIPITATION FOCUS. THERE WILL BE A WAVY FRONTAL SYSTEM ACROSS  
THE CENTRAL U.S. WITH DEEP MOISTURE STREAMING OVER IT, PROVIDING A  
FOCUS FOR HEAVY RAINFALL FROM THE MID-SOUTH EASTWARD TO THE  
MID-ATLANTIC AND NORTHEAST. THERE IS A POTENTIAL FOR LOCALIZED  
RUNOFF ISSUES FROM THE MID-SOUTH AND OHIO VALLEY/NORTHEAST DOWN  
INTO THE MID-ATLANTIC AND SOUTH/SOUTHEAST THIS WEEKEND.  
 
EXPECT WIDESPREAD RECORD BREAKING WARMTH THIS WEEKEND IN ADVANCE  
OF THE STARKLY TEMPERATURE CONTRASTING FRONT OVER THE SOUTH AND  
EAST. COLD CANADIAN AIR SURGING IN BEHIND THE FRONT ACROSS THE  
CENTRAL AND EASTERN STATES WILL SPREAD A HEAVY SNOW/ICE THREAT  
FROM THE MIDWEST/GREAT LAKES/NORTHEAST DOWN THROUGH THE SOUTHERN  
APPALACHIANS. GUIDANCE REMAINS QUITE VARIED WITH DETAILS, BUT  
SHOWS SOME SIGNAL THAT FRONTAL WAVE GENESIS COULD TRANSLATE TO AN  
ORGANIZED COASTAL LOW OVER THE WESTERN ATLANTIC SUNDAY INTO MONDAY  
THAT COULD OFFER SOME THREAT TO COASTAL AREAS AND MARINE INTERESTS.  
 
ANOTHER MULTI-DAY ROUND OF PRECIPITATION WILL MOVE THROUGH THE  
PACIFIC NORTHWEST AND NORTHERN/CENTRAL CALIFORNIA SUNDAY THROUGH  
MIDWEEK. STRONG GUST WINDS WILL ALSO ACCOMPANY THE HEAVY  
PRECIPITATION. DURING THIS TIME THE UPPER LEVEL PATTERN SLOWLY  
TRANSITIONS AS PART OF A DEVELOPING OMEGA BLOCK OVER THE NORTHEAST  
PACIFIC IN THE FORM OF A DEEPLY AMPLIFIED CLOSED UPPER LOW/TROUGH  
DIGS SLOWLY SOUTHWARD FROM THE GULF OF ALASKA TO OFFSHORE THE  
NORTHWEST. HEAVY COASTAL RAINS AND HEAVY MOUNTAIN SNOWS WILL FOCUS  
FROM THE CASCADES TO THE SIERRA INLAND TO THE NORTH-CENTRAL GREAT  
BASIN/ROCKIES.  
 
CAMPBELL/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, THE PACIFIC NORTHWEST, AND THE SOUTHWEST, SUN-TUE, JAN  
2-JAN 4.  
- HEAVY RAIN ACROSS PORTIONS OF THE SOUTHEAST, THE MID-ATLANTIC,  
THE SOUTHERN APPALACHIANS, THE OHIO VALLEY, AND THE TENNESSEE  
VALLEY, SAT-SAT, JAN 1-JAN 2.  
- HEAVY SNOW ACROSS PORTIONS OF THE GREAT BASIN, THE  
NORTHERN/CENTRAL ROCKIES, AND THE PACIFIC NORTHWEST, MON-TUE, JAN  
3-JAN 4.  
- HEAVY SNOW ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY, THE  
GREAT LAKES, AND THE UPPER MISSISSIPPI VALLEY, SAT, JAN 1.  
- SEVERE WEATHER ACROSS PORTIONS OF THE MIDDLE/LOWER MISSISSIPPI  
VALLEY, THE TENNESSEE VALLEY, THE MID-ATLANTIC, THE SOUTHERN  
APPALACHIANS, THE SOUTHEAST, AND THE OHIO VALLEY, SAT, JAN 1.  
- HIGH WINDS ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE SOUTHERN  
PLAINS, AND THE SOUTHWEST, SAT, JAN 1.  
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE PLAINS,  
THE ROCKIES, THE GREAT BASIN, AND THE UPPER/MIDDLE MISSISSIPPI  
VALLEY, SAT, JAN 1.  
 
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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