795  
FXUS02 KWBC 100623  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
122 AM EST THU JAN 10 2019  
 
VALID 12Z SUN JAN 13 2019 - 12Z THU JAN 17 2019  
   
..OVERVIEW
 
 
PROGRESSIVE AND AMPLIFIED FLOW ACROSS THE NORTH PACIFIC WILL  
CONTINUE TO BRING SIGNIFICANT STORM SYSTEMS TO THE WEST COAST  
EVERY COUPLE OF DAYS DURING THE MEDIUM RANGE PERIOD. A  
STRENGTHENING UPPER RIDGE ACROSS THE NORTHERN ROCKIES/GREAT BASIN  
WILL RESULT IN SPLIT FLOW AS THESE PACIFIC SYSTEMS MOVE EASTWARD,  
WITH ENERGY SEPARATING INTO NORTHERN AND SOUTHERN STREAM  
COMPONENTS. NORTHERN STREAM ENERGY WILL AMPLIFY AS IT ENTERS BROAD  
CYCLONIC UPPER-LEVEL FLOW EAST OF THE UPPER-LEVEL RIDGE, RESULTING  
IN FREQUENT SHORTWAVES AND MEAN UPPER TROUGHING FROM THE UPPER  
MIDWEST TO THE GREAT LAKES. A PARTIALLY PHASED SHORTWAVE WILL  
CROSS THE THE MISSISSIPPI/OHIO VALLEYS ON SUN WITH DEVELOPMENT OF  
A COASTAL LOW PRESSURE SYSTEM ALONG THE NORTH/SOUTH CAROLINA COAST  
LIKELY, WHICH SHOULD THEN TRACK NORTHEASTWARD INTO THE ATLANTIC  
OCEAN. MEANWHILE, PROGRESSIVE FLOW ACROSS THE NORTH PACIFIC WILL  
KEEP THE WEST COAST ACTIVE, WITH AN AMPLIFIED TROUGH/UPPER LOW  
REACHING CALIFORNIA SUN-MON, ANOTHER WEAKENING SYSTEM ON WED, AND  
YET ANOTHER APPROACHING BY THU.  
 
A TREND IS BECOMING EVIDENT AMONG THE GUIDANCE THAT A RATHER  
SIGNIFICANT PATTERN CHANGE COULD BEGIN TO UNFOLD TOWARD THE LATTER  
PORTION OF THE MEDIUM RANGE AND BEYOND. MODEL/ENSEMBLE SOLUTIONS  
CONTINUE TO TREND STRONGER WITH THE UPPER RIDGE ACROSS WESTERN  
NORTH AMERICA BY THE MIDDLE OF NEXT WEEK, WHILE A DOWNSTREAM UPPER  
VORTEX DEEPENS NORTH OF HUDSON BAY, SETTING UP BROAD  
NORTH-NORTHWESTERLY FLOW FROM THE ARCTIC INTO CENTRAL CANADA.  
FARTHER SOUTH ACROSS THE CONUS, THE FLOW APPEARS TO REMAIN  
PROGRESSIVE, ORIGINATING IN THE NORTH PACIFIC, WHICH SHOULD LIMIT  
THE SOUTHWARD INTRUSION OF ARCTIC AIR INTO THE CONUS FOR NOW.  
NONETHELESS, WOULD EXPECT AN AREA OF ARCTIC AIR TO BEGIN POOLING  
ACROSS CENTRAL CANADA BY THE MIDDLE OF NEXT WEEK, WITH THE  
POTENTIAL FOR INCURSIONS SOUTHWARD, ESPECIALLY INTO THE  
MIDWEST/GREAT LAKES.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
A MULTI-MODEL DETERMINISTIC (ECMWF/GFS/CMC) BLEND SERVED AS A  
STARTING POINT FOR THE FORECAST DURING DAYS 3-5 (SUN-TUE). MODELS  
STILL HAVE YET TO FULLY RESOLVE THE SPECIFIC STRUCTURE OF THE  
LEADING SHORTWAVE ENERGY CROSSING THE OHIO VALLEY ON SUN AS WELL  
AS A SECONDARY AMPLIFYING SHORTWAVE ON MON, BOTH OF WHICH PLAY A  
ROLE IN THE TIMING/TRACK OF THE LOW PRESSURE SYSTEM OFFSHORE. IN  
TERMS OF THE COASTAL LOW TRACK, GUIDANCE SEEMED VERY WELL  
CLUSTERED AROUND THE ECENS MEAN, WHICH IS VERY CLOSE TO THE  
PREFERRED WPC SOLUTION. SOLUTIONS WERE REASONABLY WELL-CLUSTERED  
WITH THE AMPLIFIED SYSTEM APPROACHING CALIFORNIA DURING THE DAY  
3-5 PERIOD, AND A CONSENSUS/MULTI-MODEL SOLUTION WAS PREFERRED  
HERE AS WELL.  
 
DURING DAYS 6-7 (WED-THU) UNCERTAINTIES BEGIN TO QUICKLY CROP UP  
IN BOTH THE NORTHERN AND SOUTHERN STREAMS. SHORTWAVE ENERGY  
CROSSING THE ROCKIES ON DAY 5 AND REACHING THE CENTRAL U.S. BY DAY  
6 HAS SHOWN QUITE A BIT OF RUN-TO-RUN VARIABILITY AMONG THE  
GUIDANCE AS TO HOW AMPLIFIED THE FEATURE WILL BECOME. ADDITIONAL  
SHORTWAVE ENERGY REACHING THE WEST COAST BY WED NIGHT/THU SHOWS  
SOMEWHAT BETTER CONSENSUS AMONG THE GUIDANCE, ESPECIALLY WITH  
RESPECT TO TIMING OF THE FEATURE. FARTHER NORTH, THE  
AFOREMENTIONED HIGHLY AMPLIFIED FLOW PATTERN DEVELOPING ACROSS  
CANADA WILL OPEN THE DOOR FOR SOUTHWARD TRANSPORT OF SHORTWAVE  
ENERGY ORIGINATING IN THE ARCTIC, WHICH GENERALLY DO A  
PARTICULARLY POOR JOB HANDLING. THE ECMWF HAS SHOWN A BIT MORE  
CONSISTENCY WITH THE NORTHERN STREAM FLOW DURING THIS TIME FRAME  
RELATIVE TO THE GFS. THE CMC WAS A BIT MORE AGGRESSIVE WITH  
LOWERING HEIGHTS ACROSS THE GREAT LAKES BY DAY 7 RELATIVE TO THE  
OTHER GUIDANCE, BUT GIVEN THE LARGE SCALE PATTERN THIS DOES NOT  
NECESSARILY SEEM UNREASONABLE. THUS THE FORECAST DURING DAYS 6-7  
WAS A BLEND OF INCREASING WEIGHT ON ENSEMBLE MEANS (ECENS AND  
NAEFS) ALONG WITH MINORITY COMPONENTS OF THE ECMWF AND CMC.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE LOW PRESSURE SYSTEM MOVING THROUGH THE SOUTHEAST U.S. AND OFF  
THE EASTERN SEABOARD SUN-MON IS EXPECTED TO PRODUCE A BAND OF  
WINTRY PRECIPITATION FROM THE OHIO VALLEY TO THE SOUTHERN  
MID-ATLANTIC, WITH HEAVY SNOW POSSIBLE FOR SOME AREAS. GUSTY WINDS  
MAY ALSO BE POSSIBLE ALONG THE MID-ATLANTIC COAST SUN NIGHT INTO  
MON AS THE SYSTEM BEGINS TO DEEPEN OFFSHORE. THE WEST COAST WILL  
REMAIN ACTIVE GIVEN THE RAPID FREQUENCY OF SHORTWAVE ENERGY AND  
FRONTAL SYSTEMS. THE HEAVIEST PRECIPITATION (LOW ELEVATION RAIN  
AND MOUNTAIN SNOW WILL BE FOCUSED ACROSS CALIFORNIA, WITH MULTIPLE  
ROUNDS OF PRECIPITATION ARE POSSIBLE THROUGH THE FORECAST PERIOD.  
 
ABOVE AVERAGE TEMPERATURES ARE EXPECTED SUN-TUE ACROSS MUCH OF THE  
CENTRAL AND NORTHERN PLAINS, WITH HIGH TEMPERATURES GENERALLY  
10-15 DEG F ABOVE AVERAGE. THE SOUTHEAST AND EASTERN SEABOARD WILL  
INITIALLY SEE BELOW AVERAGE TEMPERATURES IN THE WAKE OF THE UPPER  
TROUGH AND LOW PRESSURE SYSTEM, WITH HIGHS 5-10 DEG BELOW AVERAGE  
SUN-MON, AND MODERATING TEMPERATURES FROM TUE ONWARD.  
 
RYAN  
 
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