849  
FXUS02 KWBC 281919  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
218 PM EST TUE DEC 28 2021  
 
VALID 12Z FRI DEC 31 2021 - 12Z TUE JAN 04 2022  
 
...BITTERLY COLD TEMPERATURES TO CONTINUE INTO NEW YEAR'S DAY  
ACROSS THE NORTHERN ROCKIES/PLAINS...  
 
...HEAVY NEW YEAR'S EVE TO 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 MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A  
COMPOSITE BLEND OF THE 06 UTC GEFS ENSEMBLE MEAN AND 00 UTC  
ECMWF/CANADIAN/ECMWF ENSEMBLE MEAN THAT OFFER A SIMILAR SYNOPTIC  
PATTERN EVOLUTION DAYS 3-7 IN A PATTERN WITH BETTER THAN NORMAL  
FORECAST SPREAD AND 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. THE LATEST FEW RUNS OF THE GFS HAVE SHOWN LESS  
STELLAR RUN TO RUN CONTINUITY.  
   
..WEATHER/HAZARDS HIGHLIGHTS
 
 
AN AMPLIFIED RIDGE BUILT OVER THE EAST-CENTRAL PACIFIC WILL ALLOW  
THE DIGGING OF A SERIES OF POTENT SHORTWAVE TROUGHS AND FRONTAL  
SYSTEMS INTO THE WEST FRIDAY INTO SATURDAY ALONG WITH COLD  
TEMPERATURES AND UNSETTLED WEATHER CONDITIONS HIGHLIGHTED BY  
SOUTH-CENTRAL GREAT BASIN/ROCKIES HEAVY SNOWS AS LOCALLY ENHANCED  
BY FAVORED TERRAIN. 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. HEAVY RAINS AND SOME LOCAL RUNOFF ISSUES MAY DEVELOP  
AND SPREAD NORTHEASTWARD ACROSS THE MID-SOUTH AND OH  
VALLEY/NORTHEAST TO RING IN THE NEW YEAR. SPC ALSO OFFERS SOME  
RISK OF SEVERE WEATHER OVER THE SOUTH FRIDAY INTO SATURDAY. ARCTIC  
AIR ON THE BACKSIDE WILL MEANWHILE SPILL THROUGH THE N-CENTRAL  
U.S. TO ALSO SPREAD A RISK OF HEAVY SNOW FROM THE CENTRAL PLAINS  
TO THE MIDWEST/GREAT LAKES. WAVY FRONTAL PROGRESSION SHOULD SHIFT  
ORGANIZED RAINS MORE INTO THE MID-ATLANTIC/SOUTHEAST INTO SUNDAY  
BEFORE WORKING OFFSHORE. POST-FRONTAL COLD AIR INTRUSION MAY THEN  
FAVOR LINGERING SUNDAY SNOW/ICE CHANCES FROM THE SOUTHERN  
APPALACHIANS AND VICINITY UP THROUGH THE NORTHEAST.  
 
SUNDAY-TUESDAY OF NEXT WEEK THEN LOOKS QUITE ACTIVE FOR THE  
NORTHWEST AND NORTH-CENTRAL CALIFORNIA 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. EXPECT AN INCREASINGLY  
WINDY MULTI-DAY HEAVY PRECIPITATION EPISODE WITH MODERATE TO HEAVY  
COASTAL RAINS AND HEAVY MOUNTAIN SNOWS INLAND FROM THE CASCADES TO  
THE SIERRA.  
 
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  
 
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  
 

 
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page