542  
FXUS02 KWBC 291605  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1204 PM EDT MON OCT 29 2018  
 
VALID 12Z THU NOV 01 2018 - 12Z MON NOV 05 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE MEAN SYNOPTIC PATTERN ACROSS THE CONUS WILL BE COMPRISED OF A  
HIGH OVER THE WEST COAST WITH A TROUGH OVER THE CENTRAL/EASTERN  
STATES. SERIES OF SHORTWAVES WILL PASS WITHIN THE MEAN TROUGH,  
WHICH WILL KEEP MUCH OF THIS REGION IN AN ACTIVE WET PATTERN.  
DETERMINISTIC AND ENSEMBLE MEANS ARE IN AGREEMENT WITH THE  
LARGE-SCALE FEATURES; HOWEVER, HAS MAINTAINED RUN-TO-RUN  
VARIABILITY IN THE TIMING, LOCATION AND AMPLITUDE OF SPECIFIC  
DETAILS AND THE DEGREE OF SPREAD INCREASED FURTHER IN TIME.  
NOTICEABLE PHASING ARISES JUST PRIOR TO THE BEGINNING OF THE  
EXTENDED FORECAST PERIOD, THURSDAY MORNING, ESPECIALLY IN REGARDS  
TO WHERE ALONG THE FRONTAL BOUNDARY A WAVE OF LOW PRESSURE  
DEVELOPS AND ITS EVOLUTION AS IT LIFTS TO THE NORTHEAST WITH TIME.  
 
THE CONTINUED APPROACH OF UTILIZING A MULTI-MODEL BLEND WAS USED  
FOR THIS FORECAST. IT WAS BASED PRIMARILY ON THE ECMWF/GFS/UKMET  
WITH HEAVIER WEIGHTING OF THE GEFS, NAEFS MEAN AND ECWMF  
ENSEMBLES. BY DAYS 6-7 THE WEIGHTING OF THE DETERMINISTIC GUIDANCE  
WAS RATHER LIGHT. THE LATEST GUIDANCE PERSISTED IN DEPICTING THE  
SHORTWAVE ENERGY APPROACHING THE PACIFIC NORTHWEST ON DAY 5  
AMPLIFYING AS IT CROSSES THE ROCKIES AND CENTRAL U.S. DAYS 6-7.  
THIS FEATURE RESULTED IN EVEN MORE SPREAD IN THE HOW THE MODELS  
EVOLVE ON SUNDAY AND MONDAY.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
POTENTIALLY HEAVY CONVECTION MAY BE ONGOING AT THE BEGINNING OF  
THE EXTENDED PERIOD ON THU ACROSS PORTIONS OF THE TENNESSEE AND  
OHIO VALLEYS IN ASSOCIATION WITH THE FRONTAL WAVE AND FURTHER  
NORTH OVER THE NORTHEAST IN ASSOCIATION WITH THIS FRONTAL SYSTEM  
AS IT REACHES THE EASTERN SEABOARD. HEAVY RAIN ALSO BE POSSIBLE  
ACROSS THE PACIFIC NORTHWEST THROUGH THE WEEKEND AS UPPER  
SHORTWAVES/SURFACE FRONTS TRAVERSE THE NORTHERN PERIPHERY OF THE  
UPPER RIDGE. THESE FEATURES WILL ALSO BRING ROUNDS OF SNOW TO THE  
HIGHER ELEVATIONS OF THE NORTHERN AND PERHAPS THE CENTRAL ROCKIES.  
CHILLY CONDITIONS WILL BE PREVALENT THROUGH MOST OF THE FORECAST  
PERIOD ACROSS MUCH OF THE CENTRAL U.S. BENEATH THE PERSISTENT  
UPPER TROUGH, WHERE HIGHS WILL GENERALLY BE 5 TO 10 DEG F BELOW  
AVERAGE. MEANWHILE, ABOVE AVERAGE TEMPERATURES WILL PERSIST ACROSS  
PORTIONS OF THE WEST, FROM CALIFORNIA INTO THE GREAT BASIN, WHERE  
HIGH TEMPERATURES MAY REACH 5 TO 15 DEG F ABOVE AVERAGE.  
 
CAMPBELL  
 
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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