243  
FXUS02 KWBC 161600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST WED JAN 16 2019  
 
VALID 12Z SAT JAN 19 2019 - 12Z WED JAN 23 2019  
   
..MAJOR CENTRAL TO NORTHEASTERN U.S. ARCTIC BLAST/WINTER STORM
 
 
   
..OVERVIEW
 
 
FOR THE HOLIDAY WEEKEND, A LOW WILL SPREAD SNOW TO THE  
NORTH-CENTRAL U.S. AND NORTHEAST, RAIN TO THE SOUTH-CENTRAL U.S.  
AND SOUTHEAST, AND MIXED PRECIPITATION IN BETWEEN. ANOTHER UPPER  
LOW IS FORECAST TO MOVE THROUGH THE WEST ON DAY 4-5 (SUN-MON),  
WHICH WILL DEEPEN A TROUGH OVER THE SOUTH-CENTRAL U.S. ONCE AGAIN  
BY TUES-WED.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
DETERMINISTIC AND ENSEMBLE MODEL GUIDANCE WAS IN REASONABLY GOOD  
AGREEMENT FOR DAYS 4-5, SO THE WPC FORECASTS WERE DERIVED FROM A  
MULTI-MODEL BLEND OF THE 00Z ECMWF AND UKMET, 06Z GFS, AND NAEFS  
AND ECMWF ENSEMBLE MEANS. BY DAY 5, THE TROUGH CENTERED IN THE  
ROCKIES BEGAN TO HAVE SOME MODEL DISAGREEMENT BETWEEN THE SLOWER  
CANADIAN AND ECMWF SOLUTIONS AND THE FASTER GFS, WHICH CONTINUES  
INTO DAYS 6-7. THE 00Z GFS ESPECIALLY WAS CONSIDERABLY FASTER THAN  
THE GEFS MEAN WITH THIS FEATURE. THUS LEANED AWAY FROM THAT AND  
MORE TOWARD THE ECENS AND OPERATIONAL ECMWF, ALONG WITH THE NAEFS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
FRIGID ARCTIC AIR SPILLS ACROSS THE CENTRAL THEN EASTERN U.S. AS  
THE NORTHERN STREAM AMPLIFIES AROUND A HUDSON BAY UPPER VORTEX.  
UNDERNEATH, AMPLIFIED SOUTHERN STREAM MID-UPPER LEVEL TROUGH  
APPROACH/HEIGHT FALLS AND FAVORABLE COUPLED UPPER JET SUPPORT WILL  
SPAWN CYCLOGENESIS FROM THE SOUTH-CENTRAL TO EASTERN U.S. OVER MLK  
JR. WEEKEND. DEEPENING GULF OF MEXICO THEN ATLANTIC MOISTURE WILL  
ADVECT INLAND IN ADVANCE AND AROUND THE DEVELOPING STORM AND  
OVERRUN A SHARP ARCTIC FRONT. THE HEAVY SNOW EVENT WILL BEGIN IN  
THE SHORT RANGE IN THE CENTRAL PLAINS, AND WILL SPREAD EASTWARD ON  
DAY 4 FROM PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY THROUGH THE  
MIDWEST/OHIO VALLEY, NORTHERN APPALACHIANS, AND NORTHERN  
MID-ATLANTIC/NORTHEAST. SOME LOCATIONS COULD SEE BLIZZARD  
CONDITIONS IN THE TIGHT PRESSURE GRADIENT BETWEEN THE SURFACE LOW  
AND A STRONG ARCTIC HIGH. MEANWHILE, HEAVY WARM-SECTOR  
RAINS/STRONG CONVECTION MOVE THROUGH THE  
SOUTH/SOUTHEAST/MID-ATLANTIC AND A TRANSITION ZONE BETWEEN SNOW  
AND RAIN IS LIKELY TO INCLUDE SIGNIFICANT SLEET AND FREEZING RAIN.  
PLEASE CONSULT WPC QPF AND WINTER WEATHER FORECASTS FOR A  
PROBABILISTIC ASSESSMENT OF THE SIGNIFICANT WINTER WEATHER THREAT.  
 
UPSTREAM, PACIFIC STORM SYSTEMS WILL RELOAD WITH NEW FOCUS AS A  
HEAVY PRECIPITATION THREAT INTO THE PACIFIC NORTHWEST. WINTRY  
WEATHER SPREADS/MODERATES INLAND ACROSS THE NORTH-CENTRAL GREAT  
BASIN/ROCKIES LATER IN THE HOLIDAY WEEKEND AND THEN ACROSS THE  
CENTRAL U.S. EARLY-MID NEXT WEEK. THERE IS A SIGNAL FOR INCREASED  
MID-UPPER LEVEL TROUGH AMPLITUDE/SEPARATION OVER THE SOUTH-CENTRAL  
U.S., BUT THERE IS MORE UNCERTAINTY WITH THE SPECIFICS OF THIS  
FLOW AND ASSOCIATED SURFACE SYSTEM RESPONSE. HOWEVER, MOST  
GUIDANCE SUPPORTS AN INCREASING LEAD GULF MOISTURE INFLOW AND  
PRECIPITATION PATTERN WITH ADDITIONAL POTENTIAL FOR WINTRY WEATHER  
ON THE COOLED NORTHERN PERIPHERY HEADING INTO TUE/WED.  
 
TATE/SCHICHTEL  
 
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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