413  
FXUS02 KWBC 310702  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
201 AM EST MON DEC 31 2018  
 
VALID 12Z THU JAN 03 2019 - 12Z MON JAN 07 2019  
   
..OVERVIEW
 
 
THE MEDIUM RANGE PERIOD BEGINS WITH A CLOSED LOW OVER THE  
MISSISSIPPI VALLEY SLOWLY MOVING EASTWARD--ARRIVING IN THE  
MID-ATLANTIC BY BETWEEN DAY 4-5 (FRI-SAT) WHILE ADDITIONAL WAVES  
OF ENERGY SLIDE ACROSS THE NORTHERN TIER OF THE U.S. FOR THE  
WESTERN U.S., AN UPPER RIDGE WILL BE THE DOMINANT FEATURE STARTING  
OUT THE MEDIUM RANGE WITH A DIGGING TROUGH MOVING TOWARD THE WEST  
COAST BY DAY 4-5. THIS TROUGH WILL LIKELY MOVE INLAND ACROSS THE  
INTERMOUNTAIN WEST/GREAT BASIN BY THE END OF THE MEDIUM RANGE  
PERIOD. THIS PATTERN WILL BRING ACTIVE WEATHER ACROSS THE EASTERN  
U.S. ON DAYS 3-5, SHIFTING TO THE WEST BY DAYS 5-7.  
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
FROM THE BEGINNING, OPERATIONAL MODELS WERE NOT IN AGREEMENT WITH  
THE TROUGH/CLOSED MID-LEVEL LOW OVER THE MISSISSIPPI VALLEY. THE  
12Z ECMWF HAS A CLOSED LOW OVER THIS AREA FOR DAY 3 (THU)--WHILE  
THE 12Z GFS HAS THE TROUGH STRETCHING BACK INTO THE LOWER MS  
VALLEY/SOUTHERN PLAINS--WITH THE 18Z GFS LOOKING SIMILAR TO THIS  
SOLUTION. THE 12Z UKMET STILL REMAINS THE SLOWEST (HAS THE CLOSED  
LOW IN THE SOUTHERN PLAINS ON DAY 3). THE 12Z CMC IS THE FASTER  
SIDE (OVER THE TN/OH VALLEY). BY DAY 4, GFS WASTES NO TIME IN  
BRINGING THE CLOSED LOW OVER THE CAROLINAS, WHILE THE ECMWF IS  
OVER THE TN/OH VALLEY. THE ECMWF WITH THIS SYSTEM HAS OVERALL BEEN  
CONSISTENT WITH ITSELF WHILE THE GFS, TO SAY THE LEAST, HAS NOT  
BEEN CONSISTENT. THE 12Z ECMWF ENSEMBLE MEAN AND 12Z NAEFS WERE  
COMPARABLE TO EACH OTHER AND TO THE ECMWF--THIS FOR THE FIRST 2  
DAYS THE BLEND WAS BASED ON MOSTLY THE 12Z ECMWF/ECMWF ENSEMBLE  
MEAN/NAEFS AND A SMALL PORTION OF THE 12Z GFS.  
 
BY DAY 5, AS THE TROUGH IN THE EAST EXITS CONUS, AN INCOMING  
TROUGH IN THE PACIFIC WILL APPROACH THE WEST COAST. UNFORTUNATELY,  
OPERATIONAL MODELS STILL DO NOT COME TO A CONSENSUS. THE 12Z/18Z  
GFS BRINGS THE TROUGH INLAND VERY QUICKLY, WHILE THE 12Z ECMWF IS  
MUCH SLOWER WITH THIS EVOLUTION. THE ECMWF ENSEMBLE MEAN THE LAST  
SEVERAL RUNS HAS FAVORED THIS SLOWER SOLUTION--WITH THE GEFS MEAN  
SHOWING RUN-TO-RUN INCONSISTENCIES. THUS, THE BLEND FROM DAYS 5-7  
WAS BASED MOSTLY ON AN ECMWF/ECMWF ENSEMBLE MEAN BLEND WITH SOME  
18Z GEFS MEAN.  
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
ON DAYS 3-4, AS THE SURFACE LOW MOVES ACROSS THE SOUTHEAST AND  
INTO THE MID-ATLANTIC, PRECIPITATION WILL BE EXPECTED ACROSS THESE  
AREAS. THE HEAVIEST AXIS OF PRECIPITATION WILL LIKELY TO OCCUR IN  
THE NORTHERN PORTIONS OF THE SOUTHEAST EASTWARD INTO THE WESTERN  
CAROLINAS. THE COASTAL REGION OF THE NORTHEAST CAN ALSO EXPECT  
PRECIPITATION DURING THIS TIME--FINALLY ENDING BY SATURDAY NIGHT.  
ON THE NORTHERN END OF THIS PRECIPITATION SHIELD, THERE COULD BE  
SOME WINTRY MIX--WITH ACCUMULATING SNOW EXPECTED FOR NEW ENGLAND  
ON FRIDAY AND SATURDAY. OUT WEST, RAIN AND HIGHER ELEVATION SNOW  
WILL IMPACT THE PACIFIC NORTHWEST--WITH ACCUMULATING SNOWS  
PARTICULARLY IMPACTING THE WASHINGTON/OREGON CASCADES AND THE  
NORTHERN PORTIONS OF THE NORTHERN ROCKIES. BY DAYS 6-7 (SUN-MON),  
AS THE TROUGH APPROACHES THE WEST COAST AND MOVES INLAND,  
PRECIPITATION WILL SPREAD ACROSS CALIFORNIA AND INTO THE FOUR  
CORNERS REGION. EXPECT HIGHER ELEVATION SNOW DURING THESE DAYS  
ESPECIALLY FOR THE SIERRA NEVADA MOUNTAIN RANGE IN ADDITION TO THE  
HIGHER ELEVATIONS ACROSS THE FOUR CORNERS, AND PORTIONS OF THE  
INTERMOUNTAIN WEST.  
 
THE NORTHERN PLAINS AND UPPER MIDWEST WILL EXPERIENCE WARMER THAN  
NORMAL TEMPERATURES FROM THU-SAT, WITH ANOMALIES REACHING 15-20  
DEGREES ABOVE AVERAGE. BY SUNDAY AND INTO MONDAY, THE OHIO VALLEY  
WILL HAVE THE HIGHEST TEMPERATURE ANOMALIES--WITH 5-10 DEGREES  
ABOVE AVERAGE. THE WESTERN U.S. WILL STAY NEAR NORMAL THROUGHOUT  
THE MEDIUM RANGE PERIOD.  
 
REINHART  
 
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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