400  
FXUS02 KWBC 151613  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1112 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 00Z  
DETERMINISTIC EC AND 00 AND 06Z GFS, AS WELL AS THE EC AND GEFS  
ENSEMBLE MEANS. DID LEAN MORE TOWARD THE EC ENSEMBLE MEAN RATHER  
THAN THE GEFS FOR THE DEVELOPING NOR'EASTER, BECAUSE IT MAINTAINED  
A STRONGER LOW, CLOSER TO THE OPERATIONAL RUNS, THAN THE GEFS  
MEAN. ANOTHER MODEL DIFFERENCE THAT EXISTS IS 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  
STRENGTH AND POSITION OF 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 FOR WHETHER OR NOT TO CLOSE OFF A LOW, 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 COULD SPREAD SOME  
WINTRY WEATHER OVER THE NORTHEAST FRIDAY. UPSTREAM, A MORE ROBUST  
TROUGH EJECTING FROM THE WEST ORGANIZES OVER THE SOUTH-CENTRAL  
PLAINS WITH INCREASED 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 BETWEEN TO A MAIN LOW  
THAT LIFTS THROUGH THE EASTERN U.S. AND OFFSHORE AND A STRONG HIGH  
IN THE PLAINS. MEANWHILE, HEAVY WARM-SECTOR RAINS/CONVECTION MOVE  
THROUGH THE SOUTH/SOUTHEAST AND A TRANSITION ZONE BETWEEN SNOW AND  
RAIN IS LIKELY TO 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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