202  
FXUS02 KWBC 311900  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
159 PM EST FRI DEC 31 2021  
 
VALID 12Z MON JAN 03 2022 - 12Z FRI JAN 07 2022  
 
...MULTI-DAY COASTAL HEAVY RAIN AND MOUNTAIN FOCUSING HEAVY SNOW  
THREAT FOR THE PACIFIC NORTHWEST AND NORTHERN CALIFORNIA TO THE  
NORTHERN GREAT BASIN/ROCKIES NEXT WEEK...  
...ARCTIC BLAST TO FOCUS OVER THE NORTH-CENTRAL U.S.  
TUESDAY-FRIDAY WITH SNOW LIKELY FOR THE CHILLED GREAT LAKES STATES  
THROUGH THE INTERIOR NORTHEAST...  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS MAINLY DERIVED FROM A  
COMPOSITE OF BEST CLUSTERED GUIDANCE FROM THE 00 UTC  
ECMWF/UKMET/CANADIAN DAYS 3/4 (MONDAY-TUESDAY) ALONG WITH THE 13  
UTC NBM IN A PATTERN WITH OVERALL ABOVE NORMAL PREDICTABILITY.  
MODEL DIFFERENCES NEAR THE SURFACE BECOME INCREASINGLY PROBLEMATIC  
WEDNESDAY-FRIDAY DESPITE A GENERALLY COMPATIBLE LARGER SCALE  
PATTERN EVOLUTION ALOFT. THIS IS NOT UNUSUAL DURING THE COLD  
SEASON IN PERIODS WITH STARK BAROCLINIC ZONES AND PHASING  
UNCERTAINTIES. THE WPC MEDIUM RANGE PRODUCT SUITE IN THIS PERIOD  
WAS ACCORDINGLY DERIVED FROM A COMPOSITE OF BETTER CLUSTERED  
GUIDANCE FROM THE 06 UTC GEFS MEAN AND 00 UTC NAEFS MEAN THAT HAVE  
A COOLER ARCTIC AIRMASS OVER TIME THAN THE 00 UTC ECMWF ENSEMBLE  
MEAN. SOME ADDED INPUT FROM THE BEST SYSTEM COMPATIBLE 00 UTC  
ECMWF AND ADDITIONAL MANUAL ADJUSTMENTS ADDED SOME DETAIL  
CONSISTENT WITH THE UPPER FLOW, PATTERN RECOGNITION AND CONTINUITY.  
 
...WEATHER PATTERN AND WEATHER/HAZARDS HIGHLIGHTS..  
 
A COLD CANADIAN SURFACE HIGH WILL SETTLE FAR SOUTH ACROSS MUCH OF  
THE CENTRAL/EASTERN U.S. IN THE WAKE OF THE STRONG COLD FRONT TO  
EXIT THE EAST COAST BY MONDAY WHOSE COASTAL LOW LIFTS OFFSHORE THE  
MID-ATLANTIC. SURFACE CYCLOGENESIS ENSUES OVER THE NORTH-CENTRAL  
U.S. TUESDAY/WEDNESDAY IN RESPONSE TO AN AMPLIFYING UPPER TROUGH,  
WITH YET ANOTHER SURGE OF FRIGID AIR IN IT'S WAKE. TRAILING  
FRONTAL LOW GENESIS OFFERS SOME MODERATE TRAILING FRONTAL FOCUSING  
RAIN POTENTIAL ALONG WITH A HEAVY SNOW THREAT SPREADING MAINLY  
FROM THE GREAT LAKE STATES TO INTERIOR NEW ENGLAND NEXT  
THURSDAY/FRIDAY WITH WINDY/WRAPPED FLOW AND COLD AIR OVER THE  
LAKES ENHANCEMENT.  
 
PROTRACTED PERIODS OF HEAVY COASTAL RAINS AND HEAVY MOUNTAIN  
FOCUSING SNOWS WILL DEVELOP FROM THE NORTHWEST AND NORTHERN  
CALIFORNIA INTO THE NORTHERN GREAT BASIN THROUGH EARLY TO LATER  
NEXT WEEK AS ENERGIES FROM A MULTI-DAY PACIFIC STORM SYSTEM PRESS  
INLAND. UNLIKE RECENT EVENTS, LATEST GUIDANCE TRENDS SUGGEST THIS  
STORM EPISODE IS NOT EXPECTED TO PRODUCE HEAVY PRECIPITATION FOR  
CENTRAL/SOUTHERN CALIFORNIA. A MULTI-DAY HEAVY SNOW THREAT IS ALSO  
LIKELY FOR THE NORTH-CENTRAL ROCKIES/HIGH PLAINS AS FURTHER  
ENHANCED BY A FAVORABLE POST-FRONTAL UPSLOPE ARCTIC AIRMASS FETCH  
WITH TEMPERATURES AS COLD AS 20-40 DEGREES BELOW NORMAL OVER THE  
NORTHERN PLAINS ALONG WITH DANGEROUS WIND CHILLS.  
 
HAMRICK/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  
 

 
 

 
 
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