687  
FXUS02 KWBC 181606  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1105 AM EST FRI JAN 18 2019  
 
VALID 12Z MON JAN 21 2019 - 12Z FRI JAN 25 2019  
   
..OVERVIEW
 
 
MODELS ARE CONTINUING TO LOCK ONTO A LARGE SCALE PATTERN CHANGE  
WHERE FLOW OVER THE EAST PACIFIC OCEAN AND WESTERN NORTH AMERICA  
BECOMES AMPLIFIED THUS SETTING UP A MEAN TROUGH OVER THE EASTERN  
HALF OF THE CONTINENT. THE INCREASINGLY LARGE SCALE OF THE  
EVENTUAL MEAN PATTERN SHOULD LEAD TO BETTER THAN AVERAGE  
PREDICTABILITY OVERALL BUT EMBEDDED SHORTWAVES WILL BE SMALLER IN  
SCALE AND STILL PROVIDE MEANINGFUL UNCERTAINTY FOR SOME SENSIBLE  
WEATHER DETAILS.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
THE WINTER STORM SYSTEM IMPACTING THE LOWER 48 STATES IN THE SHORT  
RANGE PERIOD WILL BE TRACKING NORTHEAST THROUGH THE CANADIAN  
MARITIMES BY THE BEGINNING OF THE EXTENDED RANGE. A FAIRLY  
VIGOROUS WESTERN U.S. SHORTWAVE, ALONG WITH INTERACTING NORTHERN  
STREAM FLOW, WILL MOST LIKELY SUPPORT PLAINS THROUGH GREAT LAKES  
LOW PRESSURE OVER THE COURSE OF NEXT WEEK. SOME OF THE WESTERN  
ENERGY MAY ALSO PRODUCE WAVINESS ALONG THE TRAILING FRONT AS IT  
CROSSES THE EAST.  
 
CONFIDENCE IN ANY SOLUTION IS STILL ONLY MODERATE AT BEST AT THIS  
POINT AS INDIVIDUAL SOLUTIONS REMAIN SENSITIVE TO STREAM  
INTERACTION AND EXACT SMALL-SCALE DETAILS OF SHORTWAVE ENERGY.  
THERE IS EVEN MORE UNCERTAINTY REGARDING WHAT WAVINESS MAY EXIST  
ON THE TRAILING FRONT, WITH DEPENDENCE ON HOW INITIAL WESTERN  
ENERGY EVOLVES AND EVENTUALLY SOME INDIRECT INFLUENCE FROM  
UPSTREAM ENERGY REACHING WESTERN NORTH AMERICA BY TUE-WED. .  
 
FORECAST PREFERENCE USED A COMPROMISE OF THE OPERATIONAL GUIDANCE  
EARLY FOLLOWED BY GRADUAL INCREASE OF ENSEMBLE MEAN WEIGHT (00Z  
GEFS AND ECMWF MEAN) FROM 20 PERCENT EARLY TO NEARLY 50 PERCENT  
LATE IN THE PERIOD.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
COLD, BLUSTERY CONDITIONS ARE EXPECTED FOR MUCH OF THE GREAT  
LAKES, OHIO VALLEY, MID-ATLANTIC AND NORTHEAST REGIONS EARLY IN  
THE WEEK AS THE STRONG WINTER STORM SYSTEM PULLS AWAY FROM THE  
COAST. SOME LOCATIONS MAY HAVE DAILY MAXIMUM TEMPERATURES 15-30F  
BELOW NORMAL INTO EARLY. CURRENTLY, THE BEST POTENTIAL FOR ANY  
DAILY RECORDS TO BE CHALLENGED WOULD BE FOR COLD HIGHS OVER THE  
NORTHERN MID-ATLANTIC/SOUTHERN NEW ENGLAND ON MONDAY.  
 
EXPECT THE SYSTEM EMERGING FROM THE WEST TO SPREAD MOSTLY SNOW  
ACROSS PARTS OF THE GREAT BASIN AND ROCKIES, AS WELL AS, THE  
NORTHERN PLAINS ON MONDAY. THE SYSTEM WILL DRAW MOISTURE FROM THE  
GULF ONCE IT PROGRESSES EASTWARD WHICH WILL INCREASE THE POTENTIAL  
FOR HEAVY RAINFALL ACROSS THE LOWER MISSISSIPPI VALLEY AND AREAS  
TO THE NORTHEAST TUESDAY ONWARD. BEYOND THE UPPER MISSISSIPPI  
VALLEY THE HIGHEST PROBABILITY FOR SIGNIFICANT SNOWFALL SHOULD  
EXTEND ACROSS THE GREAT LAKES AND NORTHEAST WITH A POSSIBLE  
TRANSITION OF WINTRY MIX BETWEEN THIS AREA WITH RAIN TO THE SOUTH.  
ALSO NOTE THAT SNOW POTENTIAL COULD EXTEND FARTHER SOUTH  
DEPENDING ON HOW A POSSIBLE FRONTAL WAVE EVOLVES. PARTS OF THE  
CENTRAL U.S. MAY SEE A BRIEF PERIOD OF WARMTH FROM THIS SYSTEM  
MIDWEEK WITH SOME LOCATIONS HAVING DAILY MAXIMUMS 10 TO 20F WARMER  
THAN NORMAL.  
 
A FOCUSED BAND OF SHORTWAVE ENERGY AND MOISTURE WILL BRING A  
PERIOD OF ENHANCED SNOW AND LOW ELEVATION RAIN TO AREAS FROM THE  
PACIFIC NORTHWEST INTO THE NORTHERN/CENTRAL ROCKIES, MOSTLY IN THE  
TUESDAY-WEDNESDAY TIME FRAME. ADDITIONAL SHORTWAVES COULD PRODUCE  
LIGHT SNOW OVER/NEAR THE ROCKIES LATER IN THE WEEK BUT WITH LOW  
CONFIDENCE IN LOCATION AND TIMING. APPROACH OF THE BUILDING  
EASTERN PACIFIC RIDGE ALOFT WILL LIKELY LEAD TO MODERATELY ABOVE  
NORMAL TEMPERATURES OVER THE WEST COAST STATES BY MID-LATE WEEK  
BUT CENTRAL/SOUTHERN ROCKIES SHOULD REMAIN SOMEWHAT BELOW NORMAL  
THROUGH FRIDAY.  
 
CAMPBELL/RAUSCH  
 
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