378  
FXUS02 KWBC 141600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1059 AM EST MON JAN 14 2019  
 
VALID 12Z THU JAN 17 2019 - 12Z MON JAN 21 2019  
 
...HEAVY PRECIPITATION SHIFTS EASTWARD FROM CALIFORNIA THROUGH THE  
WEST THU/FRI...  
...FRIGID AIR SURGES TO THE CENTRAL U.S/NORTHEAST TO SET THE STAGE  
FOR ANOTHER MAJOR CENTRAL TO EASTERN U.S. SNOW THREAT FOR THE  
HOLIDAY WEEKEND, WITH POTENTIALLY HEAVY RAIN FARTHER SOUTH...  
 
   
..OVERVIEW
 
 
FOR THE BEGINNING OF THE FORECAST PERIOD, AN UPPER LOW ONCE AGAIN  
SHIFTS INTO THE WEST COAST. ITS ENERGY WILL HELP CREATE AN UPPER  
TROUGH DOWNSTREAM IN THE CENTRAL U.S., WHICH WILL LEAD TO SURFACE  
LOW DEVELOPMENT IN THE LEE OF THE ROCKIES. THIS SURFACE LOW IS  
EXPECTED TO SHIFT EAST AND TRANSITION INTO A NOR'EASTER, CAUSING A  
MYRIAD OF HAZARDOUS WEATHER ACROSS THE CENTRAL AND EASTERN U.S.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
OVERALL, GUIDANCE WAS IN REASONABLY GOOD AGREEMENT THROUGHOUT THE  
MEDIUM RANGE PERIOD, ADDING TO FORECAST CONFIDENCE. PREVIOUS RUNS  
OF THE GFS WERE MUCH FASTER WITH MOVING THE UPPER TROUGH AND  
ANTECEDENT SURFACE LOW ACROSS THE CENTRAL TO EASTERN U.S. THAN THE  
ECMWF SUITE, BUT THE LATEST RUNS HAVE COME INTO CLOSER AGREEMENT,  
WITH THE GFS SLOWING DOWN CONSIDERABLY AND THE EC SPEEDING UP A  
BIT. SPEED OF THE SYSTEM WILL DEPEND IN PART ON WHETHER OR NOT THE  
NORTHERN AND SOUTHERN STREAMS WILL SEPARATE OR REMAIN COMBINED AS  
ONE TROUGH. OTHER FEATURES, SUCH AS THE UPPER-LEVEL LOW MOVING  
INTO THE WEST EARLY IN THE PERIOD AS WELL AS ANOTHER UPPER TROUGH  
OR LOW APPROACHING THE SOUTHWEST BY DAY 7, ALSO SEEMED  
WELL-HANDLED. THUS, A BLEND OF THE OPERATIONAL GFS/ECMWF AND  
GEFS/ECMWF ENSEMBLE MEANS WAS UTILIZED THROUGHOUT THE FORECAST  
PERIOD.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
IN THE WEST, THE LAST IN AN UPCOMING SOUTHERN STREAM SERIES OF  
INLAND SLAMMING PACIFIC SYSTEMS THIS WEEK WILL BRING ADDITIONAL  
HEAVY PRECIPITATION TO MOSTLY CALIFORNIA AND TO A LESSER EXTENT  
THE PACIFIC NORTHWEST THU. HEAVY VALLEY RAINS/MOUNTAIN SNOWS ARE  
LIKELY WITH GUIDANCE NOW BETTER CLUSTERED VERSUS THE LAST FEW  
DAYS, BOLSTERING FORECAST CONFIDENCE. WITH A HEALTHY INFLUX OF  
MOISTURE, PRECIPITATION WILL WORK INLAND THROUGH THE INTERMOUNTAIN  
WEST/GREAT BASIN/ROCKIES LATE THURSDAY AND FRIDAY 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.  
 
MEANWHILE, DOWNSTREAM SURGES OF FRIGID CANADIAN AIR INTO THE  
CENTRAL U.S. BECOME MORE SIGNIFICANT THURSDAY THROUGH THE WEEKEND  
AS THE NORTHERN STREAM AMPLIFIES AROUND A WOBBLING HUDSON BAY  
UPPER VORTEX. LEADING LOWS THU-FRI SPREAD SOME MODEST SNOWS OVER  
THE NORTHEAST QUARTER OF THE NATION. UPSTREAM, A MORE ROBUST  
SYSTEM EJECTING FROM THE WEST ORGANIZES OVER THE SOUTHERN PLAINS  
WITH INCREASED GULF OF MEXICO MOISTURE AND LIFT THROUGH ARKANSAS  
SATURDAY AS AN ARCTIC FRONT TO THE NORTH PUSHES THROUGH THE  
NORTHEAST. AS PRECIPITATION OVERRUNS THE COLD AIRMASS TO THE  
NORTH, HEAVY SNOW WILL SPREAD OUT OF THE CENTRAL PLAINS THROUGH  
THE MIDWEST/OHIO VALLEY THEN MID-ATLANTIC/NORTHEAST AS POTENTIALLY  
HEAVY WARM-SECTOR RAINS/CONVECTION MOVE THROUGH THE SOUTH. THERE  
IS AN INCREASING SIGNAL IN GUIDANCE/IMPROVED MODEL AND ENSEMBLE  
CLUSTERING FOR A SIGNIFICANT AND WIDESPREAD HEAVY SNOW/ICE EVENT  
TO THE NORTH OF A SUBSEQUENT MAIN LOW TRACK THROUGH THE EAST THEN  
UP OFF THE COAST. PLEASE CONSULT WPC DAY 4-7 QPF AND WINTER  
WEATHER OUTLOOK FOR A PROBABILISTIC ASSESSMENT OF THE COAST TO  
COAST 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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