282  
FXUS02 KWBC 240651  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
150 AM EST MON DEC 24 2018  
 
VALID 12Z THU DEC 27 2018 - 12Z MON DEC 31 2018  
 
...SIGNIFICANT WINTER STORM TO MOVE INTO THE UPPER MIDWEST  
THURSDAY AND GREAT LAKES ON FRIDAY...  
   
..OVERVIEW
 
 
A POWERFUL AND IMPACTFUL WINTER STORM WILL EXIT THE PLAINS  
WEDNESDAY AND PUSH THROUGH THE UPPER MIDWEST THURSDAY BRINGING  
HEAVY WIND-DRIVEN SNOW AND LOCALLY HEAVY WARM SECTOR CONVECTIVE  
RAINS THROUGH THE SOUTH. THE SYSTEM WILL MOVE OFF THE  
NORTHEAST/MID-ATLANTIC COAST SATURDAY AS THE FRONT SETTLES INTO  
THE GULF OF MEXICO. ANOTHER STORM WILL DIG THROUGH THE  
WEST/SOUTHWEST IN THE WAKE OF THE FIRST STORM TO SPREAD  
PRECIPITATION (MOSTLY SNOW) THROUGH THE GREAT BASIN/SOUTHWEST AND  
CENTRAL/SOUTHERN ROCKIES.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
A DETERMINISTIC BLEND OF THE 12Z FV3-GFS AND ECMWF/UKMET/CANADIAN  
SERVED AS A GOOD STARTING POINT FOR THE MAJOR SYSTEM THROUGH THE  
NORTHERN TIER THU-FRI AS THE GFS RUNS HAVE BEEN A BIT TOO QUICK  
BUT THE ECMWF RUNS A BIT TOO SLOW. FOR SATURDAY THROUGH MONDAY,  
THE FLOW FROM THE PACIFIC INTO/THROUGH THE WEST BECOMES  
INCREASINGLY UNCERTAIN WITH DIVERGENCE IN THE ENSEMBLES IN THE  
EVOLUTION OF UPPER TROUGHING. THE GFS/GEFS HAVE BEEN MORE BULLISH  
ON A CLOSED/CUTOFF UPPER LOW OVER NW MEXICO THIS WEEKEND WHILE THE  
ECMWF RUNS HAVE GENERALLY FAVORED A WEAKER POSITIVELY-TILTED  
TROUGH FARTHER EAST. ENSEMBLES HAVE NOT SHOWN MUCH, IF ANY,  
CONTRACTION EITHER OVER THE CONUS OR UPSTREAM SO DID NOT LEAN ON  
ANY ONE/GROUP OF DETERMINISTIC MODELS. A BLEND BETWEEN THE GEFS  
MEAN AND ECMWF ENSEMBLE MEAN SUFFICED FOR NOW WHICH WAS  
QUICKER/WEAKER/FARTHER EAST THAN THE GFS AND  
SLOWER/STRONGER/FARTHER WEST THAN THE ECMWF. TELECONNECTIONS STILL  
SUPPORT SUCH AN IDEA THAT WOULD ALLOW SOME RIDGING INTO CALIFORNIA  
SUNDAY. IN THE EAST, NORTHERN STREAM WOULD TAKE THE TROUGH QUICKLY  
OUT OF THE CENTRAL ROCKIES BETWEEN AN UPPER LOW OVER HUDSON BAY  
AND SUBTROPICAL RIDGING OVER THE BAHAMAS, LEAVING A WAVY FRONT  
ACROSS THE GULF AND SOUTHEAST (WITH POSSIBLE WAVES ALONG IT).  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
PRECIPITATION IN ASSOCIATION WITH THE MAJOR PLAINS/MIDWEST SYSTEM  
WILL PUSH EASTWARD THURSDAY WITH SNOW (HEAVY AT TIMES WITH  
INCREASING WIND AND POSSIBLE BLIZZARD CONDITIONS) MAKING TRAVEL  
DIFFICULT IF NOT IMPOSSIBLE. SEVERAL INCHES OF SNOW ARE LIKELY  
OVER A LARGE AREA WITH OVER A FOOT QUITE POSSIBLE FOR SOME AREAS,  
ESPECIALLY THROUGH PARTS OF EASTERN SD/NORTHEASTERN KS TO  
MINNESOTA/WISCONSIN/U.P. OF MICHIGAN AS THE SURFACE LOW TRACKS  
TOWARD LAKE MICHIGAN. PLEASE CONSULT THE LATEST WPC WINTER WEATHER  
OUTLOOK PROBABILITIES FOR A DAILY GRAPHICAL DEPICTION OF THE BEST  
CHANCE OF SNOW. IN THE WARM SECTOR, RAINFALL COULD BECOME LOCALLY  
HEAVY IN THE SOUTH AS THE SYSTEM INFUSES GULF MOISTURE NORTHWARD  
UP AND OVER THE WARM FRONT. SEVERAL INCHES OF RAIN ARE POSSIBLE IN  
SOME AREAS WITH A MORE WIDESPREAD 1-2+" LIKELY. THE MAIN LOW  
SHOULD EXIT THROUGH SOUTHERN ONTARIO AND NORTHERN NEW ENGLAND  
WHERE SOME ONSET FROZEN PRECIPITATION (PERHAPS APPRECIABLE  
FREEZING RAIN AS WARM AIR ADVANCES OVER IN SITU LOWER-LEVEL COLD  
AIR) IS LIKELY. NEXT SYSTEM INTO THE WEST ON THE HEELS OF THE LEAD  
STORM WILL BRING MORE DYNAMICALLY DRIVEN SNOW AND SOME LOWER  
ELEVATION RAIN FROM THE NORTHWEST AND GREAT BASIN INTO THE FOUR  
CORNERS REGION. ANOTHER COLD FRONT WILL ENTER THE PACIFIC  
NORTHWEST WITH LIMITED MOISTURE EAST OF THE CASCADES. STATIONARY  
FRONT IN THE SOUTHEAST COULD SUPPORT A SURFACE WAVE RIDING ALONG  
IT THAT MAY SPREAD SOME RAIN/SNOW THROUGH THE  
SOUTHEAST/MID-ATLANTIC EARLY NEXT WEEK.  
 
TEMPERATURES WILL BE COOLER THAN AVERAGE IN THE WEST BEHIND THE  
FRONT BUT WILL BE WELL ABOVE AVERAGE OVER THE MISSISSIPPI VALLEY  
EASTWARD (10-30 DEG F ANOMALIES ESPECIALLY OVERNIGHT) UNTIL THE  
COLD FRONT MOVES THROUGH. WITH REINFORCING TROUGHING INTO THE WEST  
LATER IN THE WEEK, TEMPERATURES WILL STAY BELOW AVERAGE FROM THE  
GREAT BASIN/ROCKIES INTO THE PLAINS, ESPECIALLY OVER NEWLY  
SNOW-COVERED AREAS. COOLER AIR WILL FILTER INTO THE EAST NEXT  
WEEKEND AS THE FRONT SINKS INTO THE GULF AND NORTHERN FLORIDA.  
CENTRAL/SOUTHERN FLORIDA WILL STAY UNDER THE INFLUENCE OF  
SUBTROPICAL RIDGING AND ABOVE AVERAGE TEMPERATURES.  
 
FRACASSO  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND 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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