671  
FXUS02 KWBC 292045  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
344 PM EST WED DEC 29 2021  
 
VALID 12Z SAT JAN 01 2022 - 12Z WED JAN 05 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 PRIMARILY DERIVED FROM A  
COMPOSITE OF BEST CLUSTERED GUIDANCE FROM THE 06 UTC GFS/GEFS, THE  
00 UTC ECWMF/ECMWF ENSEMBLE MEAN AND THE 13 UTC NATIONAL BLEND OF  
MODELS. THE SYNOPTIC PATTERN FOR THIS PERIOD STILL SHOWS ABOVE  
AVERAGE PREDICTABILITY WHILE THE BLEND TENDS TO MITIGATE LINGERING  
TIMING AND PHASING DIFFERENCES WITH EMBEDDED SYSTEMS THAT  
INCREASES LOCAL FOCUS UNCERTAINTY. WPC PRODUCT CONTINUITY IS WELL  
MAINTAINED.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
AN AMPLIFIED UPPER TROUGH OVER THE WEST WILL EJECT ACROSS A VERY  
SNOWY SOUTH-CENTRAL ROCKIES TO THE PLAINS SATURDAY. EJECTING  
ENERGIES IN TWO STREAMS WILL THEN GENERATE SYSTEMS TO ENHANCE AN  
EMERGING CENTRAL TO EASTERN U.S. PRECIPITATION FOCUS. DEEP  
MOISTURE STREAMING INTO A STRONG AND WAVY FRONTAL SYSTEM OFFERS  
POTENTIAL FOR HEAVY RAINFALL AND LOCALIZED RUNOFF ISSUES FROM THE  
MID-SOUTH AND OHIO VALLEY/NORTHEAST DOWN INTO THE MID-ATLANTIC AND  
SOUTH/SOUTHEAST THIS WEEKEND. SOME STORMS ACROSS THE SOUTH MAY  
ALSO BE SEVERE, PER SPC. EXPECT WIDESPREAD RECORD BREAKING WARMTH  
THIS WEEKEND IN ADVANCE OF THE STARKLY TEMPERATURE CONTRASTING  
FRONT OVER THE SOUTH AND EAST. COLD POST-FRONTAL AIR WORKING  
ACROSS THE CENTRAL TO EASTERN U.S. SHOULD MEANWHILE 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.  
 
WELL UPSTREAM, SUNDAY-WEDNESDAY WILL BECOME QUITE STORMY FOR THE  
NORTHWEST AND THE NORTH-CENTRAL CALIFORNIA AS 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. THIS WILL RESULT IN A MULTI-DAY  
HEAVY WIND/PRECIPITATION EVENT. HEAVY COASTAL RAINS AND HEAVY  
MOUNTAIN SNOWS WILL FOCUS FROM THE CASCADES TO THE SIERRA INLAND  
TO THE NORTH-CENTRAL GREAT BASIN/ROCKIES.  
 
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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