615  
FXUS02 KWBC 221554  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1053 AM EST SAT DEC 22 2018  
 
VALID 12Z TUE DEC 25 2018 - 12Z SAT DEC 29 2018  
   
..SIGNIFICANT CENTRAL U.S. STORM AFTER CHRISTMAS
 
 
   
..OVERVIEW
 
 
A STORM SYSTEM MOVING THROUGH THE SOUTHWEST STATES NEXT TUESDAY  
(CHRISTMAS DAY) WILL LIFT THROUGH THE CENTRAL PLAINS WED-THU AND  
INTENSIFY, SETTING THE STAGE FOR A MAJOR RAIN AND SNOWSTORM FOR  
MUCH OF THE CENTER OF THE COUNTRY. THE SYSTEM WILL MOVE INTO THE  
GREAT LAKES ON FRIDAY AND THEN OFF THE NORTHEAST/MID-ATLANTIC  
COAST NEXT SATURDAY AS ANOTHER STORM MOVES THROUGH THE  
WEST/SOUTHWEST AND TEXAS. THE LARGE SCALE REMAINS QUITE  
PREDICTABLE BUT THE IMPORTANT DETAILS WILL BE REFINED OVER THE  
NEXT SEVERAL DAYS.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
A MAJORITY DETERMINISTIC MODEL BLEND (INCLUDING THE 00Z  
ECMWF/GFS/FV3) SERVED AS A GOOD STARTING POINT DURING DAYS 3-5  
(TUE-THU) GIVEN THE GOOD ENSEMBLE AGREEMENT THROUGH THE END OF THE  
FORECAST PERIOD, WITH INCREASED WEIGHT PLACED TOWARD THE 00Z  
ECENS/NAEFS MEANS BY DAYS 6-7 (FRI-SAT). THE 06Z GFS EVENTUALLY  
BECAME FASTER THAN THE GUIDANCE CONSENSUS WITH THE PROGRESSION OF  
THE LOW PRESSURE SYSTEM THROUGH ACROSS THE GREAT LAKES FRI-SAT, SO  
THE 00Z GFS (WHICH WAS RIGHT IN LINE WITH THE CONSENSUS) WAS USED  
INSTEAD. OVERALL, ONLY MINOR CHANGES TO CONTINUITY WERE MADE AS  
THE OVERALL CONSENSUS BLEND HAS BEEN FAIRLY STEADY.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
EARLY IN THE WEEK THE PRECIPITATION FOCUS WILL BE ON THE SOUTHWEST  
AS THE PACIFIC SYSTEM PUSHES THROUGH NORTHERN ARIZONA. AS THE  
SYSTEM STARTS TO LIFT NORTHEASTWARD THROUGH KANSAS, PRECIPITATION  
WILL EXPAND AROUND AND AHEAD OF THE DEEPENING LOW 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 OVER PARTS OF KANSAS AND NEBRASKA THURSDAY.  
SEVERAL INCHES OF SNOW ARE LIKELY OVER A LARGE AREA WITH OVER A  
FOOT QUITE POSSIBLE FOR SOME AREAS. PLEASE CONSULT THE LATEST  
WINTER WEATHER PROBABILITIES FOR A DAILY GRAPHICAL DEPICTION. IN  
THE WARM SECTOR, RAINFALL COULD BECOME LOCALLY HEAVY NEAR THE GULF  
COAST AS THE SYSTEM INFUSES GULF MOISTURE NORTHWARD UP AND OVER  
THE WARM FRONT.  
 
TEMPERATURES WILL TREND COOLER THAN AVERAGE IN THE WEST BEHIND THE  
FRONT TUESDAY BUT WILL BE ABOVE AVERAGE OVER THE PLAINS AND MUCH  
OF THE EAST AS HIGH PRESSURE MOVES OFF THE MID-ATLANTIC COAST. AS  
THE SURFACE LOW DEEPENS OVER KANSAS, MILDER AIR WILL BE DRAWN  
NORTHWARD FROM THE MISSISSIPPI VALLEY EASTWARD AS THE SYNOPTIC  
WARM FRONT AND LEADING WARM FRONT SURGE NORTHWARD. THIS WILL YIELD  
TEMPERATURES 10-20 DEG F ABOVE AVERAGE, ESPECIALLY OVERNIGHT,  
PROGRESSING EASTWARD AHEAD OF THE COLD FRONT.  
 
RYAN/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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