055  
FXUS02 KWBC 280708  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
208 AM EST TUE DEC 28 2021  
 
VALID 12Z FRI DEC 31 2021 - 12Z TUE JAN 04 2022  
 
...BITTERLY COLD TEMPERATURES TO CONTINUE THURSDAY-SATURDAY ACROSS  
PORTIONS OF THE NORTHERN PLAINS...  
 
...HEAVY RAIN ACROSS ACROSS PARTS OF THE TENNESSEE/OHIO VALLEY NEW  
YEAR'S EVE/NEW YEAR'S DAY...  
 
   
..OVERVIEW AND GUIDANCE
 
 
AN AMPLIFIED RIDGE WILL BE ANCHORED OVER THE NORTHERN PACIFIC  
OCEAN THROUGH THIS PERIOD, WHICH WILL CONTINUE TO SUPPORT AN UPPER  
TROUGH OVER THE WESTERN U.S.; THIS PATTERN WILL FAVOR VERY BRISK  
TEMPERATURES. A SEPARATE PIECE OF ENERGY WITHIN THE LARGER SCALE  
TROUGH SHOULD TRACK A LITTLE OFFSHORE SOUTHERN CALIFORNIA  
THURSDAY-FRIDAY. THE OVERALL PATTERN WILL BEGIN TO TRANSITION BY  
THE WEEKEND AS A NEW RIDGE BUILDS FARTHER WEST, LEADING TO A  
DEEPENING TROUGH OVER THE NORTHEAST PACIFIC AND RENEWED MOISTURE  
FEED INTO THE NORTHWEST U.S. THE TROUGH AND ASSOCIATED MOISTURE  
WILL TRACK INTO THE CENTRAL AND EASTERN PART OF THE COUNTRY. A  
MUCH WEAKER WAVY FRONTAL SYSTEM WILL DEPART FROM THE EAST LATE  
THIS WEEK.  
 
THE LATEST MODEL GUIDANCE CONTINUES TO HAVE SIMILAR PATTERNS AND  
EVOLUTION THROUGH THE EXTENDED THEREFORE CHOOSE TO TAKE A  
MULTI-MODEL APPROACH; THIS ALSO HELPS MAINTAIN CONTINUITY FROM THE  
PREVIOUS FORECAST. THE WPC BLEND USED THE 12Z ECWMF/CMC/UKMET,  
12/18Z GFS INITIALLY AND GRADUALLY INCREASED THE USE OF THE EC  
ENSEMBLE MEANS AND THE GEFS MEANS TROUGH THE MIDDLE AND LATER  
PERIODS.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
LINGERING SHOWERS ARE EXPECTED ACROSS PARTS OF THE SOUTHEAST NEAR  
A WAVY COLD FRONT ALONG WITH SNOW OVER THE NORTHEAST NEAR THE  
PARENT LOW PRESSURE. SCATTERED TO WIDESPREAD SHOWERS AND  
THUNDERSTORMS WILL MOVE ACROSS THE PLAINS TOWARDS THE EASTERN U.S.  
AS A LOW PRESSURE SYSTEM AND ASSOCIATED FRONTS DEVELOPS. A PLUME  
OF DEEP MOISTURE WILL ACCOMPANY THIS SYSTEM AND INTENSIFY OVER THE  
TENNESSEE VALLEY; WHERE CONDITIONS WILL BE VERY FAVORABLE FOR  
MODERATE TO HEAVY RAINFALL TO OCCUR. THERE WILL BE AN ELEVATED  
RISK FOR LOCAL FLOODING CONCERNS AS THIS REGION HAS HAD RECENT  
SOAKING RAINS TO LOWER LOCAL FLASH FLOOD GUIDANCE. EXPECT SOME  
WINTRY WEATHER IN THE NORTHERN SIDE OF THE PRECIPITATION  
SHIELD--FROM PARTS OF THE NORTHERN/CENTRAL PLAINS THROUGH THE  
MIDWEST, GREAT LAKES, AND NORTHEAST. THE INTENSITY AND STORM  
TRACK, ALONG WITH ANY WAVES ALONG THE BOUNDARY, WILL DETERMINE THE  
THE LOCATION AND AMOUNTS.  
 
HEAVY MOUNTAIN SNOW WILL SPREAD ACROSS THE PACIFIC NORTHWEST AND  
NORTHERN ROCKIES THURSDAY AHEAD OF AN APPROACHING SHORTWAVE.  
ABUNDANT MOISTURE WILL BE DIRECTED ONSHORE SOUTHERN CALIFORNIA  
WITH THE UPPER TROUGH/POSSIBLE CLOSED LOW POSITIONED OFFSHORE.  
MODERATE TO LOCALLY HEAVY RAINFALL MAY BE POSSIBLE IN THE LOWER  
ELEVATIONS; WITH SNOW SPREADING ACROSS THE HIGHER TERRAIN  
ESPECIALLY OVER THE COLORADO ROCKIES WITH THE MERGING OF NORTHERN  
AND SOUTHERN STREAM UPPER SYSTEMS. A THIRD SYSTEM NEARING THE  
PACIFIC NORTHWEST WILL USHER IN AN ADDITIONAL ROUND OF HEAVY  
MOUNTAIN SNOW BY THE WEEKEND. LOWER ELEVATION RAIN COULD BECOME  
MODERATE TO HEAVY FROM THE PACIFIC NORTHWEST INTO NORTHWESTERN  
CALIFORNIA BY EARLY NEXT WEEK.  
 
THE FRIGID AIRMASS OVER THE NORTHERN TIER SHOULD PERSIST THROUGH  
AT LEAST SATURDAY WITH THE DAILY READINGS AVERAGING 20 TO 35  
DEGREES BELOW AVERAGE FOR THE END OF THE YEAR. A FEW LOCATIONS IN  
FAR NORTHERN NORTH DAKOTA AND MONTANA MAY STAY BELOW 0 F EVEN INTO  
NEXT WEEKEND, DESPITE TEMPERATURES MODERATING SLIGHTLY AS THE WEEK  
PROGRESSES. GUSTY WINDS WILL CREATE SOME DANGEROUS WIND CHILL  
VALUES OF BELOW 0 F. TEMPERATURES ARE ALSO LIKELY TO BE BELOW  
NORMAL BY ABOUT 5-15 DEGREES ACROSS THE REST OF THE WESTERN U.S.  
THROUGH SUNDAY. WARM AND MILD WEATHER IS EXPECTED ACROSS THE  
SOUTHEAST AND MID-ATLANTIC INTO SUNDAY, WITH DAILY TEMPERATURE  
READINGS OF 15 TO 25 DEGREES WARMER THAN NORMAL FROM THE SOUTHERN  
PLAINS TO THE OHIO VALLEY AND EAST INTO THE MID-ATLANTIC REGION.  
 
CAMPBELL/RAUSCH  
 
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 CENTRAL  
GREAT BASIN, THE PACIFIC NORTHWEST, AND THE NORTHERN GREAT BASIN,  
SUN-MON, JAN 2-JAN 3.  
- HEAVY PRECIPITATION ACROSS PORTIONS OF THE SOUTHWEST, THU-FRI,  
DEC 30-DEC 31.  
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE  
CENTRAL APPALACHIANS, THE TENNESSEE VALLEY, THE MIDDLE MISSISSIPPI  
VALLEY, THE MID-ATLANTIC, THE SOUTHERN APPALACHIANS, THE  
SOUTHEAST, AND THE OHIO VALLEY, SAT-SUN, JAN 1-JAN 2.  
- HEAVY SNOW ACROSS PORTIONS OF THE PACIFIC NORTHWEST AND THE  
NORTHERN GREAT BASIN, THU, DEC 30.  
- HEAVY SNOW ACROSS PORTIONS OF THE GREAT LAKES AND THE UPPER  
MISSISSIPPI VALLEY, SAT, JAN 1.  
- SEVERE WEATHER ACROSS PORTIONS OF THE SOUTHEAST, THE MIDDLE  
MISSISSIPPI VALLEY, THE LOWER MISSISSIPPI VALLEY, THE OHIO VALLEY,  
AND THE TENNESSEE VALLEY, SAT, JAN 1.  
- HIGH WINDS ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE CENTRAL  
PLAINS, THE NORTHERN PLAINS, AND THE NORTHERN ROCKIES, THU, DEC 30.  
- 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, THU-SAT, DEC  
30-JAN 1.  
- MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE CENTRAL  
PLAINS, THE MIDDLE MISSISSIPPI VALLEY, THE GREAT LAKES, THE UPPER  
MISSISSIPPI VALLEY, AND THE NORTHERN PLAINS, 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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