443  
FXUS02 KWBC 310658  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
157 AM EST FRI DEC 31 2021  
 
VALID 12Z MON JAN 3 2022 - 12Z FRI JAN 7 2022  
 
...COASTAL HEAVY RAIN AND MOUNTAIN FOCUSING HEAVY SNOW THREAT FROM  
NORTHERN CALIFORNIA TO WASHINGTON...  
...ANOTHER ARCTIC BLAST FOR THE NORTH-CENTRAL U.S.  
TUESDAY-THURSDAY WITH SNOW LIKELY FOR THE GREAT LAKES AND INTERIOR  
NORTHEAST...  
 
   
..WEATHER PATTERN OVERVIEW
 
 
A COLD CANADIAN SURFACE HIGH WILL SETTLE SOUTHWARD ACROSS MUCH OF  
THE CENTRAL/EASTERN U.S. IN THE WAKE OF THE STRONG COLD FRONT THAT  
WILL BE EXITING THE EAST COAST FOR THE BEGINNING OF THE WEEK.  
SURFACE CYCLOGENESIS ENSUES OVER THE NORTHERN PLAINS BY TUESDAY IN  
RESPONSE TO AN AMPLIFYING UPPER TROUGH, AND ANOTHER SURGE OF  
ARCTIC AIR BEHIND IT. ANOTHER LOW PRESSURE SYSTEM IS ON THE  
HORIZON TO CLOSE OUT THE WEEK ACROSS THE EAST COAST, AND A  
DISTURBANCE ALSO TAKES AIM AT THE PACIFIC NORTHWEST AROUND THIS  
SAME TIME.  
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE 00Z MODEL GUIDANCE SUITE APPEARS TO BE IN ABOVE AVERAGE  
AGREEMENT ON THE SYNOPTIC SCALE WITH MORE DIFFERENCES NOTED IN  
MESOSCALE FEATURES REGARDING THE LOW PRESSURE SYSTEMS EXPECTED TO  
AFFECT THE CONTINENTAL U.S. TIMING DIFFERENCES ARE MORE APPARENT  
BY WEDNESDAY ACROSS THE MIDWEST AND GREAT LAKES REGION, WITH THE  
GFS SLOWER AND A BIT MORE AMPLIFIED WITH THE TROUGH, AND THE  
CMC/UKMET SLIGHTLY STRONGER WITH THE SOUTHERN STREAM SHORTWAVE  
CROSSING TEXAS, ALTHOUGH THESE DIFFERENCES ARE WELL WITHIN THE  
ENSEMBLE SPREAD. BY THE END OF THE WEEK, THE GFS IS NOT AS  
AMPLIFIED WITH THE SYSTEM NEAR THE EAST COAST COMPARED TO THE  
CMC/ECMWF, ALTHOUGH THEIR OVERALL PLACEMENT IS SIMILAR WITH THE  
SURFACE LOW. THERE IS STILL VERY GOOD AGREEMENT ON ANOTHER COLD  
SURFACE HIGH SETTLING SOUTHWARD ACROSS THE PLAINS BY FRIDAY.  
 
TAKING THESE FACTORS INTO ACCOUNT, THE WPC FORECAST WAS PRIMARILY  
BASED ON A MULTI-DETERMINISTIC MODEL BLEND THROUGH EARLY  
WEDNESDAY, AND THEN ECMWF/GFS/SOME CMC WITH GRADUALLY INCREASING  
USE OF THE GEFS/ECENS FOR THURSDAY AND FRIDAY.  
   
..SENSIBLE WEATHER AND HAZARDS
 
 
HEAVY COASTAL RAIN AND HEAVY MOUNTAIN SNOW IS EXPECTED FROM  
NORTHERN CALIFORNIA TO WESTERN WASHINGTON FOR EARLY TO MIDDLE PART  
OF THE WEEK AS A STORM SYSTEM MOVES INLAND ACROSS THE PACIFIC  
NORTHWEST. UNLIKE RECENT EVENTS, THIS STORM IS NOT CURRENTLY  
EXPECTED TO PRODUCE HEAVY PRECIPITATION FOR CENTRAL/SOUTHERN  
CALIFORNIA. THE SURFACE LOW OVER THE NORTH-CENTRAL U.S. FOR  
TUESDAY-WEDNESDAY WILL LIKELY HAVE A SWATH OF LIGHT TO MODERATE  
SNOW, WITH SOME BLOWING/DRIFTING SNOW AS WINDS INCREASE WITH THE  
ARCTIC AIRMASS MOVING INTO THE REGION. DEPENDING ON WHAT HAPPENS  
ALONG THE EAST COAST LATE IN THE WEEK, MODERATE TO LOCALLY HEAVY  
RAIN AND SNOW FOR THE APPALACHIANS MAY BE SOMETHING WORTH  
MONITORING.  
 
IN THE TEMPERATURE DEPARTMENT, THERE WILL BE A RETURN TO  
SEASONABLY COLD CONDITIONS ACROSS MUCH OF THE DEEP SOUTH AND THE  
EAST COAST AFTER DAYS OF WELL ABOVE AVERAGE TEMPERATURES AND  
HUMIDITY LEVELS. THERE IS LIKELY A BRIEF MODERATION ACROSS THE  
PLAINS AND MIDWEST STATES ON TUESDAY AHEAD OF THE NEXT ARCTIC  
FRONT, WHICH WILL HERALD A RETURN TO FRIGID CONDITIONS ACROSS THE  
NORTHERN PLAINS AND UPPER MIDWEST BY WEDNESDAY AND BEYOND, WITH  
HIGHS RUNNING A GOOD 15-30 DEGREES BELOW SEASONAL AVERAGES IN MANY  
CASES. THIS WILL EQUATE TO SUBZERO HIGH TEMPERATURES ONCE AGAIN  
ACROSS PORTIONS OF NORTHERN MONTANA, NORTH DAKOTA, AND NORTHERN  
MINNESOTA. WIND CHILLS WILL ALSO REACH HAZARDOUS LEVELS FOR THESE  
SAME AREAS. OUT WEST, READINGS ARE LIKELY TO BE WITHIN 10 DEGREES  
EITHER SIDE OF AVERAGE FOR MOST AREAS NEXT WEEK WEST OF THE  
CONTINENTAL DIVIDE.  
 
HAMRICK  
 
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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