404  
FXUS02 KWBC 020257  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
956 PM EST TUE JAN 01 2019  
 
VALID 12Z SAT JAN 05 2019 - 12Z WED JAN 09 2019  
   
..OVERVIEW
 
 
AS A NEGATIVELY TILTED TROUGH STRENGTHENS OFFSHORE WESTERN NORTH  
AMERICA, MID-LEVEL HEIGHT ANOMALIES BECOME EVER MORE ANOMALOUS  
ACROSS THE MIDWEST AND GREAT LAKES. THIS SUPPORTS A STRENGTHENING  
NEGATIVELY TILTED TROUGH WITH AN EMBEDDED UPPER LOW ACROSS  
ATLANTIC CANADA WITH TIME.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
BROADLY, THE GUIDANCE SHOWS REASONABLE AGREEMENT BETWEEN THE  
DETERMINISTIC AND ENSEMBLE MEAN GUIDANCE. DETAIL ISSUES ARE  
NUMEROUS, THOUGH MAINLY DUE TO VARIABLE STRENGTH MORESO THAN  
PROGRESSION WHEN COMPARED TO THIS TIME YESTERDAY. THE ONLY MODEL  
THAT APPEARED TO BE A NOTABLE OUTLIER WAS THE 12Z CANADIAN FROM  
LATE TUESDAY INTO NEXT WEDNESDAY.  
 
AS SUCH, THE 500 HPA HEIGHTS, PRESSURES, WINDS, AND FRONTS BEGAN  
WITH AN EVEN BLEND OF THE 12Z CANADIAN/12Z UKMET/12Z ECMWF/18Z  
GFS. THE ECMWF AND BIAS-CORRECTED NAEFS WERE INTRODUCED ON MONDAY  
WITH INCREASING WEIGHT BY NEXT WEDNESDAY, WHICH THE CANADIAN WAS  
SLOWLY PHASED OUT BY MID NEXT WEEK. THIS LED TO SOME SLOWING OF  
THE SYSTEM EXPECTED TO MOVE FROM MID-CONTINENT ACROSS THE GREAT  
LAKES AND NORTHEAST EARLY TO MID NEXT WEEK, BUT OTHERWISE RATHER  
GOOD CONTINUITY. THE REMAINDER OF THE LOWER 48 GRIDS WERE  
COMPOSED OF A MORE EVEN BLEND BETWEEN THE DETERMINISTIC AND  
ENSEMBLE MEAN GUIDANCE THROUGH THE PERIOD TO ACCOUNT FOR  
UNCERTAINTY IN THESE MORE VARIABLE QUANTITIES (TEMPERATURE, DEW  
POINT, CLOUDS, AND PRECIPITATION CHANCES).  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE OVERALL PATTERN SHOULD BE FAVORABLE FOR SIGNIFICANT RAINFALL  
AND HIGH ELEVATION SNOW NEAR THE WEST COAST DUE TO PERSISTENT  
SOUTHWESTERLY FLOW OFF THE PACIFIC. AREAS NEAR NORTHERN  
CALIFORNIA WITH BE WET AT LOWER ELEVATION/WHITE AT ELEVATION SOME  
LOCATIONS POSSIBLY RECEIVING AT LEAST 5-10 INCHES LIQUID SATURDAY  
INTO NEXT WEDNESDAY. FAVORED LOCATIONS OVER WESTERN  
WASHINGTON/OREGON AND THE NORTHERN CONTINENTAL DIVIDE WILL LIKELY  
SEE SIGNIFICANT TOTALS AS WELL. IN LESS EXTREME FASHION SOME  
MOISTURE SHOULD EXTEND FARTHER SOUTHWARD OVER CALIFORNIA, ARIZONA,  
AND THE INTERIOR WEST/ROCKIES. DEPENDING ON HOW SYSTEMS  
MATERIALIZE NEAR THE WEST COAST, THERE COULD BE AREAS WITH STRONG  
WINDS.  
 
OVER THE EAST, THE SYSTEM TRACKING BY THE MID-ATLANTIC COAST THIS  
WEEKEND SHOULD PRODUCE SOME AREAS OF LOCALLY MODERATE TO HEAVY  
RAINFALL FROM THE MID-ATLANTIC INTO SOUTHERN NEW ENGLAND, JUST  
NORTH OF THE UPPER LOW TRACK. THE MAJORITY OF PRECIPITATION WITH  
THIS SYSTEM SHOULD BE IN THE FORM OF RAIN. ANY WINTRY PRECIP  
TYPES SHOULD BE CONFINED TO THE VERY NORTHERN/NORTHWESTERN FRINGE  
OF THE MOISTURE SHIELD. A WAVY FRONTAL SYSTEM EMERGING FROM THE  
PLAINS MAY BRING AN EPISODE OF LIGHT TO MODERATE PRECIPITATION TO  
PARTS OF THE EASTERN HALF OF THE LOWER 48 DURING THE LATTER HALF  
OF THE PERIOD. WINTRY PRECIP TYPES SHOULD AGAIN BE CONFINED TO  
MORE NORTHERN LATITUDES.  
 
TEMPERATURES ARE EXPECTED TO BE SLIGHTLY BELOW AVERAGE ACROSS THE  
SOUTHWEST SATURDAY. OTHERWISE, MILD TO SEASONALLY WARM  
TEMPERATURES ARE EXPECTED, WITH TEMPERATURES NEAR TO ABOVE AVERAGE  
ELSEWHERE AND ELSEWHEN ACROSS THE LOWER 48 DURING THE MEDIUM RANGE  
PERIOD. SOME LOCATIONS OVER THE EXTREME NORTHERN TIER AND MIDWEST  
COULD SEE BOUTS OF 20F+ ABOVE NORMAL TEMPERATURES SATURDAY THROUGH  
TUESDAY.  
 
ROTH  
 
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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