665  
FXUS02 KWBC 151601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1100 AM EST TUE JAN 15 2019  
 
VALID 12Z FRI JAN 18 2019 - 12Z TUE JAN 22 2019  
 
...ANOTHER MAJOR CENTRAL TO EASTERN U.S. SNOWSTORM IS FORECAST,  
WITH ARCTIC COLD AIR INVOLVED...  
   
..OVERVIEW
 
 
A TROUGH MOVING INTO THE WESTERN U.S. ON DAY 3 (FRI) WILL AID IN  
SURFACE CYCLOGENESIS IN THE LEE OF THE ROCKIES. THIS SURFACE LOW  
WILL TRACK ACROSS THE CENTRAL AND EASTERN U.S., CREATING A VARIETY  
OF HAZARDOUS WEATHER. ANOTHER TROUGH IS FORECAST TO APPROACH AND  
MOVE THROUGH THE WEST BY DAY 6-7.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
MODEL GUIDANCE IS IN GENERALLY GOOD AGREEMENT IN THE LARGE SCALE,  
AND HAS BEEN FOR THE LAST DAY OR TWO. THUS WAS ABLE TO MAINTAIN  
CONTINUITY WITH PREVIOUS WPC FORECASTS BY USING A BLEND OF THE  
OPERATIONAL EC AND 00 AND 06Z GFS, AS WELL AS THE EC AND GEFS  
ENSEMBLE MEANS. THE MODEL DIFFERENCES THAT EXIST INCLUDE THE  
DEGREE OF NORTHERN AND SOUTHERN STREAM FLOW SEPARATION IN BOTH THE  
FIRST TROUGH ON DAY 4 AND THE TROUGH ON DAY 6-7, WHICH WILL AFFECT  
THE SURFACE LOWS. THE EC HAS SHOWN A CLOSED UPPER LOW IN THE  
SOUTHERN PLAINS ON DAY 4 FOR A COUPLE OF RUNS, ALONG WITH THE  
UKMET. THE OPERATIONAL GFS HAS TRENDED THAT DIRECTION TOO SO  
ELECTED TO INCLUDE A CLOSED LOW AT 500 MB FOR DAY 4 (SAT). FOR THE  
SECOND TROUGH, MODELS HAVE NOT BEEN TRENDING ANY PARTICULAR  
DIRECTION, SO WILL HAVE TO KEEP WATCHING TO SEE IF A TREND  
EMERGES.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
AMPLIFIED SOUTHERN STREAM MID-UPPER LEVEL TROUGH ENERGY/HEIGHT  
FALLS DIGS THROUGH THE SOUTHWEST FRIDAY WITH POOLED MOISTURE AND  
PRECIPITATION WORKING THROUGH THE INTERMOUNTAIN WEST/GREAT  
BASIN/ROCKIES WITH WINDY CONDITIONS AND VALLEY RAIN/MOUNTAIN SNOW.  
SNOW LEVELS WILL FALL AS HEIGHTS LOWER WHICH WILL TURN SOME LOWER  
ELEVATIONS OVER TO SNOW AS PRECIPITATION DIMINISHES SATURDAY.  
PACIFIC STORM SYSTEMS RELOAD FARTHER TO THE NORTH LATER FOR THE  
HOLIDAY WEEKEND TO THEN FOCUS AN ASSOCIATED HEAVY PRECIPITATION  
THREAT INTO/ACROSS THE NORTHWEST.  
 
DOWNSTREAM SURGES OF FRIGID ARCTIC AIR INTO THE CENTRAL U.S.  
FRIDAY THROUGH THE WEEKEND OCCUR AS THE NORTHERN STREAM AMPLIFIES  
AROUND A HUDSON BAY UPPER VORTEX. A LEAD SYSTEM WILL SPREAD SOME  
WINTERY WEATHER OVER THE NORTHEAST FRIDAY. UPSTREAM, A MORE ROBUST  
SYSTEM EJECTING FROM THE WEST ORGANIZES OVER THE SOUTH-CENTRAL  
PLAINS WITH INCREASED LEAD GULF OF MEXICO MOISTURE AND LIFT UP  
THROUGH THE EAST-CENTRAL U.S. SATURDAY AS AN ARCTIC FRONT TO THE  
NORTH PUSHES THROUGH THE NORTHEAST. AS PRECIPITATION OVERRUNS THE  
ARCTIC AIRMASS TO THE NORTH, HEAVY SNOW WILL SPREAD OUT OF THE  
CENTRAL PLAINS THROUGH THE MIDWEST/OHIO VALLEY THEN  
MID-ATLANTIC/NORTHEAST THROUGH THE HOLIDAY WEEKEND ALONG WITH SOME  
THREAT OF BLIZZARD CONDITIONS IN THE TIGHT PRESSURE GRADIENT  
AROUND A MAIN LOW THAT LIFTS THROUGH THE EASTERN U.S. AND  
OFFSHORE. MEANWHILE, HEAVY WARM-SECTOR RAINS/CONVECTION MOVE  
THROUGH THE SOUTH/SOUTHEAST AND A TRANSITION ZONE BETWEEN SNOW AND  
RAIN WILL INCLUDE SIGNIFICANT SLEET AND FREEZING RAIN. PLEASE  
CONSULT WPC DAY 4-7 QPF AND WINTER WEATHER OUTLOOK FOR A  
PROBABILISTIC ASSESSMENT OF THE SIGNIFICANT WINTER WEATHER THREAT.  
 
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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