616  
FXUS02 KWBC 290630  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
229 AM EDT MON OCT 29 2018  
 
VALID 12Z THU NOV 01 2018 - 12Z MON NOV 05 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
A MEAN UPPER-LEVEL TROUGH IS EXPECTED TO REMAIN GENERALLY IN PLACE  
ACROSS THE CENTRAL U.S. DURING THE MEDIUM RANGE, WHILE RIDGING  
DOMINATES OFF THE WEST COAST. SHORTWAVE ENERGY CROSSING THE NORTH  
PACIFIC WILL INTERACT WITH ADDITIONAL ENERGY FROM HIGHER LATITUDES  
ACROSS WESTERN CANADA, RESULTING IN A SERIES OF AMPLIFYING  
SHORTWAVES CROSSING THE CENTRAL/EASTERN U.S., MAINTAINING THE MEAN  
TROUGH. WHILE MODEL GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT ON  
THE LARGE SCALE PATTERN, SIGNIFICANT DIFFERENCES EXIST (AND GROW  
THROUGH TIME) WITH RESPECT TO THE DETAILS OF INDIVIDUAL FEATURES.  
 
MODELS SHOW TIMING DIFFERENCES STARTING ON DAY 3 (THU) FOR THE  
FRONTAL WAVE CROSSING THE LOWER MISSISSIPPI AND TENNESSEE VALLEYS.  
ADDITIONAL SHORTWAVE ENERGY IS EXPECTED TO QUICKLY DIVE SOUTHEAST  
ACROSS THE NORTHERN PLAINS AND MIDWEST ON THU-FRI, REACHING THE  
OHIO VALLEY BY DAY 5 (SAT). MODELS SHOW BOTH TIMING AND AMPLITUDE  
DIFFERENCES WITH THIS SYSTEM, WITH THE GFS AND UKMET REPRESENTING  
THE MORE AMPLIFIED SIDE OF THE SPREAD AND THE CMC THE LEAST  
AMPLIFIED. TO RESOLVE THESE DIFFERENCES, A MULTI-MODEL BLEND  
APPROACH WAS USED FOR DAYS 3-5, BASED PRIMARILY ON THE  
ECMWF/GFS/UKMET. BY DAYS 6-7 (SAT-SUN) MODEL DIFFERENCES CONTINUE  
TO QUICKLY ESCALATE, WITH DETERMINISTIC GUIDANCE LOSING MUCH OF  
ITS USEFULNESS. SHORTWAVE ENERGY APPEARS LIKELY TO REACH THE  
PACIFIC NORTHWEST ON DAY 5 WHICH SHOULD THEN AMPLIFY AS IT CROSSES  
THE ROCKIES AND CENTRAL U.S. DAYS 6-7. DETERMINISTIC MODEL  
SOLUTIONS RANGE FROM A VERY AMPLIFIED WAVE (AND SURFACE LOW  
PRESSURE SYSTEM) ACROSS THE NORTH CENTRAL U.S. BY DAY 6-7 ON THE  
ECMWF, TO FLOW QUICKLY TENDING TOWARD ZONAL ON THE CMC. AS A  
RESULT OF THE MODEL SPREAD AND VARIABILITY, LEANED HEAVILY TOWARD  
ECENS/GEFS ENSEMBLE MEANS BY DAYS 6-7.  
 
   
..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. ADDITIONAL  
AREAS OF LOCALLY HEAVY RAIN WILL BE POSSIBLE THROUGH THE END OF  
THE WEEK 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.  
 
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  
 

 
 
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