642  
FXUS02 KWBC 141610  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1109 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 A SOUTHERN STREAM SERIES OF INLAND  
SLAMMING PACIFIC SYSTEMS THIS WEEK WILL BRING ADDITIONAL HEAVY  
PRECIPITATION TO THE PACIFIC NORTHWEST AND CALIFORNIA 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 AND THEN MID-ATLANTIC/NORTHEAST AS  
POTENTIALLY HEAVY WARM-SECTOR RAINS/CONVECTION MOVE THROUGH THE  
SOUTH. THE TRANSITION ZONE BETWEEN THE SNOW AND RAIN WILL LIKELY  
INCLUDE SLEET AND FREEZING RAIN WITH THIS OVERRUNNING SIGNAL.  
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page