184  
FXUS02 KWBC 251909  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION...AMENDED  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
209 PM EST TUE DEC 25 2018  
 
VALID 12Z FRI DEC 28 2018 - 12Z TUE JAN 01 2019  
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
A BLEND OF THE NON-06Z/NON-12Z GFS GUIDANCE (00Z/12Z ECMWF,  
00Z/12Z CANADIAN, AND 00Z/12Z UKMET WITH THE 00Z/06Z/12Z GFS  
PARALLEL/FV3 AS REASONABLE ALTERNATIVES) SUFFICED GIVEN THE GOOD  
OVERALL AGREEMENT WITH THE SYSTEMS MOVING THROUGH THE WEST AND  
DOWNSTREAM EASTERN RIDGE WHICH MAINTAINED GOOD CONTINUITY FROM THE  
PREVIOUS SHIFT. THIS ACCOUNTS FOR THE OPERATIONAL GFS'S RECENT  
FORTNIGHT OF INCONSISTENCY WITH SYSTEMS MOVING ACROSS THE NORTH  
PACIFIC. WITH TIME, 00Z ECMWF AND 00Z BIAS-CORRECTED NAEFS  
ENSEMBLE MEANS WERE INCLUDED INTO THE PRESSURES/500 HPA HEIGHT  
PREFERENCE MIX.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
LOCALLY HEAVY RAINFALL IN THE SOUTHEAST WILL BE ONGOING FRIDAY AS  
THE SNOW WINDS DOWN OVER THE UPPER MIDWEST/GREAT LAKES (AND EXITS  
THE NORTHEAST) WHILE THE LOW AND FRONT MOVE TO THE EAST.  
CONCURRENTLY, THE SYSTEM WILL SINK THROUGH THE SOUTHWEST WITH MORE  
DYNAMICALLY-DRIVEN SNOW AND SOME LOWER ELEVATION RAIN INTO THE  
FOUR CORNERS REGION (ESPECIALLY NEW MEXICO). NEXT PACIFIC SYSTEM  
ENTERS LATE SATURDAY INTO SUNDAY WITH WIDESPREAD BUT MOSTLY LIGHT  
TO LOCALLY MODEST RAIN/SNOW THROUGH MUCH IN THE INTERIOR WEST  
CONTINUING ON MONDAY. THAT SURFACE LOW WILL MOVE ALONG THE  
US/CANADIAN BORDER AND DRAG ITS COLD FRONT TO THE SOUTH AND EAST.  
ALL THE WHILE, FRONT IN THE GULF WILL LINGER/WAVER AND SEND A  
COUPLE LOW PRESSURE CENTERS ALONG IT THROUGH THE SOUTHEAST WHICH  
WILL SPREAD SOME RAIN OVER AL/GA/SC/NC BUT PERHAPS TO THE  
MASON-DIXON LINE -- LIKELY RAIN BUT SOME ELEVATION SNOW.  
 
TEMPERATURES WILL BE COOLER THAN AVERAGE IN THE WEST AND PLAINS  
BEHIND THE DEPARTING GREAT LAKES STORM, WITH COLDEST ANOMALIES  
(10-20F BELOW AVERAGE) LIKELY FOCUSED OVER THE HIGH PLAINS AND  
VICINITY. AHEAD OF IT, MUCH ABOVE AVERAGE WARMTH (PLUS 10-30F  
ANOMALIES) WILL BE DRAWN INTO AREAS EAST OF THE MISSISSIPPI VALLEY  
FRI/SAT UNTIL THE COLD FRONT MOVES THROUGH. WITH REINFORCING  
TROUGHING INTO THE WEST, 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 IN THE  
WAKE OF A COLD FRONTAL PASSAGE BUT WITH NEAR AVERAGE TEMPERATURES  
FOR LATE DECEMBER CONSIDERING THE ABOVE AVERAGE MID-LEVEL HEIGHTS.  
CENTRAL AND SOUTHERN FLORIDA WILL STAY UNDER THE INFLUENCE OF  
SUBTROPICAL RIDGING AND CONTINUE WITH ABOVE AVERAGE TEMPERATURES.  
 
ROTH/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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