656  
FXUS02 KWBC 260550  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1249 AM EST WED DEC 26 2018  
 
VALID 12Z SAT DEC 29 2018 - 12Z WED JAN 02 2019  
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
POSITIVELY-TILTED TROUGHING WILL RELOAD IN THE WEST AS SUBTROPICAL  
UPPER RIDGING LINGERS OVER THE BAHAMAS. THIS ALLOWS NORTHERN  
STREAM FLOW TO PROGRESS ALONG THE US/CANADIAN BORDER TO THE SOUTH  
OF AN UPPER LOW OVER HUDSON BAY. THE RECENT 12Z/25 FV3-GFS/ECMWF  
REPRESENT A GOOD DETERMINISTIC WEIGHT TO THE FORECAST ALONG WITH  
PARTS OF THE UKMET AND CANADIAN (EARLY IN THE PERIOD). A FRONT  
WILL LINGER OVER THE GULF OF MEXICO WITH SURFACE WAVES MOVING  
NORTHEASTWARD THROUGH THE SOUTHEAST AS A PACIFIC SYSTEM PUSHES  
EAST SUN-TUE FROM NORTHWESTERN MONTANA TO THE GREAT LAKES. THE  
OPERATIONAL 12Z/18Z GFSS WERE NOT INCLUDED DUE TO ITS HANDLING OF  
A PACIFIC TROUGH THAT SHOULD CLOSE OFF NEAR 38N/150W EARLY  
SATURDAY. ITS 26/00Z RUN APPEARED MUCH MORE IN LINE. TRENDED  
TOWARD THE ECMWF ENSEMBLE MEAN BY NEXT WEDNESDAY AS THE GEFS MEAN  
WAS LIKELY TOO FAR EAST WITH THE TROUGH DUE TO UPSTREAM  
MISHANDLING OF THE PACIFIC.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
COLD FRONT IN THE EAST WILL LINGER IN THE GULF THROUGH THE PERIOD,  
SPREADING RAIN OVER THE SOUTHEAST IN BATCHES AS A SFC WAVE OR TWO  
RIDE ALONG THE BOUNDARY. THIS MAY EVEN FALL AS SNOW ON THE  
NORTHERN FRINGE GIVEN SUFFICIENTLY COLD AIR. NEXT PACIFIC SYSTEM  
ENTERS LATE SATURDAY INTO SUNDAY WITH WIDESPREAD BUT MOSTLY LIGHT  
TO LOCALLY MODEST RAIN/SNOW THROUGH MUCH OF THE INTERIOR WEST  
CONTINUING ON MONDAY BUT WINDING DOWN. THAT SURFACE LOW WILL MOVE  
ALONG THE US/CANADIAN BORDER AND DRAG ITS COLD FRONT TO THE SOUTH  
AND EAST. THIS WILL ALLOW GULF MOISTURE TO AGAIN FLOW NORTHWARD  
AND EXPAND/ENHANCE THE RAIN SHIELD THROUGH THE SOUTHEAST NEXT  
MONDAY/TUESDAY DEPENDING ON HOW THE FRONT IN THE GULF RESPONDS.  
 
TEMPERATURES WILL BE COOLER THAN AVERAGE IN THE WEST AND PLAINS  
WITH COLDEST ANOMALIES (10-20F BELOW AVERAGE) LIKELY FOCUSED OVER  
THE HIGH PLAINS AND SOUTHERN ROCKIES/WEST TEXAS. MUCH ABOVE  
AVERAGE WARMTH (PLUS 10-30F ANOMALIES) WILL BE DRAWN NORTHWARD  
AHEAD OF THE FRONT SATURDAY ALONG/EAST OF THE APPALACHIANS. COOLER  
AIR WILL FILTER INTO THE EAST IN THE WAKE OF THE COLD FRONTAL  
PASSAGE SATURDAY 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.  
 
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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