634  
FXUS02 KWBC 290626  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
126 AM EST WED DEC 29 2021  
 
VALID 12Z SAT JAN 01 2022 - 12Z WED JAN 05 2022  
 
...BITTERLY COLD TEMPERATURES TO CONTINUE INTO NEW YEAR'S DAY  
ACROSS THE NORTHERN ROCKIES/PLAINS...  
 
...HEAVY NEW YEAR'S DAY HEAVY SNOWS THREAT FOR THE SOUTH-CENTRAL  
GREAT BASIN/ROCKIES...  
 
...HEAVY RAIN/CONVECTION THREAT FROM THE MID-SOUTH/OHIO VALLEY TO  
THE MID-ATLANTIC/SOUTHEAST NEW YEAR'S EVE INTO NEW YEAR'S DAY...  
...BACKSIDE HEAVY SNOW THREAT MEANWHILE SHIFTS FROM THE CENTRAL  
PLAINS AND MIDWEST/GREAT LAKES/NORTHEAST DOWN THROUGH THE SOUTHERN  
APPALACHIANS...  
 
...MULTI-DAY HEAVY RAIN AND TERRAIN SNOW THREAT SUNDAY-TUESDAY  
FROM THE NORTHWEST TO NORTH-CENTRAL CALIFORNIA...  
 
   
..GUIDANCE AND PREDICTABILITY ASSESSMENT
 
 
THE WPC MODEL BLEND WAS COMPRISED OF EQUAL PARTS OF THE 12Z  
ECWMF/EC ENSEMBLE MEAN/CMC/GEFS MEAN AS THEY CONTINUED TO HAVE  
SIMILAR PATTERN EVOLUTION AND MAINTAINED CONTINUITY WITH THE  
PREVIOUS FORECAST.  
THE SYNOPTIC PATTERN FOR THE EXTENDED PERIOD ARE STILL SHOWING  
ABOVE AVERAGE PREDICTABILITY. THE COMPOSITE BLEND TENDS TO  
MITIGATE SMALL-MODERATE SCALES TIMING AND PHASING DIFFERENCES WITH  
EMBEDDED SYSTEMS THAT REMAINS AN ISSUE THAT INCREASES LOCAL FOCUS  
UNCERTAINTY.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
A SERIES OF SHORTWAVES WILL DIG THROUGH THE AMPLIFIED RIDGE OVER  
THE EAST-CENTRAL PACIFIC OCEAN; WHICH WILL SEND FRONTAL SYSTEMS  
INTO THE WEST FRIDAY INTO SATURDAY IN ADDITION TO COLD  
TEMPERATURES ACROSS THE SOUTH-CENTRAL GREAT BASIN AND ROCKIES WITH  
LOCALLY ENHANCED SNOWFALL. EJECTING UPPER TROUGH ENERGIES IN TWO  
STREAMS OUT FROM THE WEST WILL GENERATE SYSTEMS AND ENHANCE AN  
EMERGING EAST-CENTRAL U.S. PRECIPITATION FOCUS WITH PROGRESSION  
OUT ACROSS THE CENTRAL AND EASTERN U.S. AS AN UPPER RIDGE ERODES  
OVER THE SOUTHEAST. DEEP MOISTURE STREAMING INTO THE FRONTAL  
SYSTEM OVER THE CENTRAL/SOUTH-CENTRAL PORTION OF THE COUNTRY WILL  
LEAD TO HEAVY RAINFALL AND LOCALIZED RUNOFF. FLOODING CONCERNS MAY  
BE ELEVATED ESPECIALLY ACROSS THE MID-SOUTH AND OHIO  
VALLEY/NORTHEAST TO RING IN THE NEW YEAR. SOME OF THESE STORMS  
ACROSS THIS REGION MAY ALSO BE SEVERE, PER SPC.  
 
COLDER AIR WILL FILTER INTO THE CENTRAL U.S. CAUSING TEMPERATURES  
TO SIGNIFICANTLY DROP AND WILL ALSO SPREAD THE RISK FOR HEAVY SNOW  
FROM THE CENTRAL PLAINS TO THE GREAT LAKES REGION. WAVY FRONTAL  
PROGRESSION SHOULD SHIFT ORGANIZED RAINS MORE INTO THE  
MID-ATLANTIC/SOUTHEAST INTO SUNDAY BEFORE WORKING OFFSHORE. WITH  
THE COLDER AIR MAKING ITS WAY TOWARD THE APPALACHIANS, LINGERING  
SUNDAY SNOW/ICE CHANCES FROM THE SOUTHERN APPALACHIANS AND  
VICINITY UP THROUGH THE NORTHEAST MAY BE POSSIBLE.  
 
SUNDAY-TUESDAY OF NEXT WEEK WILL BE ACTIVE FOR A MAJORITY OF THE  
PACIFIC NORTHWEST AND THE NORTH-CENTRAL PARTS OF CALIFORNIA AS THE  
UPPER LEVEL PATTERN 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 WINDY AND  
HEAVY PRECIPITATION COUPLE OF DAYS. MODERATE TO HEAVY COASTAL  
RAINS AND HEAVY MOUNTAIN SNOWS INLAND FROM THE CASCADES TO THE  
SIERRA CAN BE EXPECTED.  
 
CAMPBELL  
 
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-TUE, JAN 2-JAN 4.  
- HEAVY PRECIPITATION ACROSS PORTIONS OF THE NORTHEAST AND THE  
GREAT LAKES, SAT, JAN 1.  
- HEAVY PRECIPITATION ACROSS PORTIONS OF THE SOUTHWEST, FRI, DEC  
31.  
- HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL/SOUTHERN APPALACHIANS,  
THE TENNESSEE VALLEY, THE MID-ATLANTIC, THE SOUTHEAST, AND THE  
OHIO VALLEY, SAT-SUN, JAN 1-JAN 2.  
- HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL/SOUTHERN ROCKIES, THE  
CENTRAL GREAT BASIN, THE CENTRAL PLAINS, AND THE SOUTHWEST, FRI,  
DEC 31.  
- HEAVY SNOW ACROSS PORTIONS OF THE GREAT LAKES AND THE UPPER  
MISSISSIPPI VALLEY, SAT, JAN 1.  
- SEVERE WEATHER ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY,  
THE LOWER MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE  
TENNESSEE VALLEY, FRI, DEC 31.  
- SEVERE WEATHER ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY,  
THE TENNESSEE VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE SOUTHERN  
APPALACHIANS, THE SOUTHEAST, AND THE OHIO VALLEY, SAT, JAN 1.  
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE UPPER  
MISSISSIPPI VALLEY, THE PACIFIC NORTHWEST, THE NORTHERN ROCKIES,  
THE NORTHERN GREAT BASIN, AND THE NORTHERN PLAINS, FRI-SAT, DEC  
31-JAN 1.  
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE  
NORTHERN/CENTRAL PLAINS, THE MIDDLE MISSISSIPPI VALLEY, THE GREAT  
LAKES, AND THE UPPER MISSISSIPPI VALLEY, SAT-SUN, JAN 1-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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