747  
FXUS02 KWBC 250649  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
149 AM EST TUE DEC 25 2018  
 
VALID 12Z FRI DEC 28 2018 - 12Z TUE JAN 01 2019  
   
..OVERVIEW
 
 
SIGNIFICANT WINTER STORM IN THE SHORT RANGE WILL EXIT THROUGH THE  
GREAT LAKES/NORTHEAST FRIDAY AS ITS ATTENDANT COLD FRONT SINKS  
INTO THE GULF OF MEXICO. IN THE WEST, ANOTHER UPPER TROUGH AND  
SURFACE COLD FRONT WILL PUSH INTO THE SOUTHWEST/FOUR CORNERS  
FRI-SUN AS ANOTHER PACIFIC SYSTEM COMES ASHORE WA/OR SUNDAY.  
LINGERING FRONT IN THE GULF WILL HAVE SURFACE WAVES OF LOW  
PRESSURE MOVE ALONG THE BOUNDARY THROUGH THE SOUTHEAST SUN-TUE  
WITH MOSTLY RAIN BUT PERHAPS SOME NORTHERN PERIPHERY AND HIGHER  
ELEVATION SNOW.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
DETERMINISTIC BLEND SUFFICED TO START THE PERIOD GIVEN THE GOOD  
OVERALL AGREEMENT WITH THE EXITING SYSTEM THROUGH SOUTHERN ONTARIO  
FRIDAY. TO THE WEST, THE LARGE DISAGREEMENT BETWEEN THE GEFS/ECMWF  
ENSEMBLES HAS NARROWED BUT NOT DISAPPEARED -- FIRST OVER THE  
NORTHEAST PACIFIC AND THEN INTO THE SOUTHWEST. PREFERRED THE  
12Z/24 ECMWF-LED CONSENSUS (WITH THE CANADIAN AND FV3-GFS) THAT  
ALLOWED FOR A MORE SEPARATED PACIFIC UPPER TROUGH TO PUSH INTO  
WA/OR QUICKER THAN THE 12Z/18Z GFS (WHICH WAS CONSOLIDATED/SLOWER  
WITH THE NORTHERN STREAM). DOWNSTREAM, TREND SEEMS TO FAVOR A  
WEAKER AND NOT TOTALLY CLOSED OFF UPPER LOW SUNDAY OVER NW MEXICO  
SOUTH OF THE AZ/NM BORDER WHICH YIELDS SOMETHING IN BETWEEN THE  
QUICKER PREVIOUS RUNS OF THE ECMWF AND MUCH SLOWER RUNS OF THE  
GFS. THE 12Z/24 ECMWF/CANADIAN AND FV3-GFS OFFERED A GOOD BASE TO  
COUPLE WITH THE ENSEMBLES WHICH MAINTAINED GOOD CONTINUITY FROM  
THE PREVIOUS SHIFT. WITH UPPER RIDGING CENTERED OVER THE BAHAMAS  
(AND NO REASON TO ABATE) CONTINUED TROUGHING IS FAVORED IN THE  
WEST INTO THE START OF NEXT WEEK AND THE NEW YEAR (TUE JAN 1).  
NORTHERN STREAM WILL CONTINUE TO ZIP ALONG THE US/CANADIAN BORDER  
AND THE SYSTEM MOVING THROUGH IDAHO SUNDAY WILL MOVE INTO THE  
GREAT LAKES AROUND NEXT TUESDAY.  
 
   
..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  
POST-FROPA BUT ONLY TO NEAR AVERAGE FOR LATE DECEMBER.  
CENTRAL/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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