208  
FXUS02 KWBC 231601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST SUN DEC 23 2018  
 
VALID 12Z WED DEC 26 2018 - 12Z SUN DEC 30 2018  
 
...SIGNIFICANT SOUTHERN ROCKIES/PLAINS/MIDWEST/GREAT LAKES WINTER  
STORM WED-FRI...  
   
..OVERVIEW
 
 
A POWERFUL AND IMPACTFUL WINTER STORM WILL LIFT FROM THE SOUTHERN  
ROCKIES UP THROUGH THE PLAINS TO THE MIDWEST WED-THU BRINGING  
HEAVY WIND-DRIVEN COLD SECTOR SNOWS OVER THE N-CENTRAL U.S. AND  
LOCALLY HEAVY WARM SECTOR CONVECTIVE RAINS INTO THE SOUTH. THE  
SYSTEM WILL MOVE INTO THE GREAT LAKES ON FRIDAY AND THEN 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 SNOWS) THROUGH THE GREAT BASIN/SOUTHWEST AND  
S-CENTRAL ROCKIES.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THE WPC MEDIUM RANGE PRODUCT SUITE WAS PRIMARILY DERIVED FROM A  
COMPOSITE BLEND OF THE 00 UTC GFS/ECMWF AND GEFS/NAEFS?ECMWF  
ENSEMBLE MEANS DAYS 4-7. APPLIED INCREASINGLY MORE WEIGHT TO  
ENSEMBLE GUIDANCE OVER TIME AMID GROWING EMBEDDED SYSTEM  
TIMING/STRENGTH DIFFERENCES. OVERALL, LEANED A BIT MORE WEIGHTING  
TOWARD THE LESS PROGRESSIVE SOLUTION ENVELOPE GIVEN THE TENDANCY  
IN GUIDANCE OVER THE LAST FEW DAYS TO OFFER A PATTERN WITH  
UPSTREAM AMPLIFICATION OVER THE PACIFIC AND ALASKA REGIONS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
A MAIN WEATHER THREAT FOCUS WILL BE ON THE MAJOR SYSTEM IN THE  
PLAINS BY WEDNESDAY AS IT LIFTS NORTHEASTWARD. PRECIPITATION WILL  
EXPAND AROUND AND AHEAD OF THE DEEPENING LOW AND COLD FRONT WITH  
THE FLOW OUT OF THE GULF. TO THE NORTHWEST OF THE SURFACE LOW,  
SNOW WILL COME DOWN HEAVY AT TIMES WITH INCREASING WIND AND  
POSSIBLE BLIZZARD CONDITIONS (BLOWING AND DRIFTING SNOW WITH  
LIMITED VISIBILITY) THURSDAY. THIS WILL MAKE 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  
FROM NW KANSAS/NE COLORADO NORTHEASTWARD TO MINNESOTA/WISCONSIN 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 DOWN INTO 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 DOWN INTO TO THE FOUR CORNERS REGION AND  
S-CENTRAL ROCKIES.  
 
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). 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.  
 
SCHICHTEL  
 
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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