681  
FXUS02 KWBC 181606  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1206 PM EDT THU OCT 18 2018  
 
VALID 12Z SUN OCT 21 2018 - 12Z THU OCT 25 2018  
 
...GUIDANCE/PREDICTABILITY ASSESSMENT AND WEATHER  
HIGHLIGHTS/THREATS...  
 
MODEL AND ENSEMBLE FORECASTS SEEM REASONABLY WELL CLUSTERED SUN  
INTO TUE, BOLSTERING FORECAST CONFIDENCE TO ABOVE NORMAL LEVELS  
WITH PREFERENCE OF A COMPOSITE GUIDANCE SOLUTION. THE PATTERN IS  
HIGHLY AMPLIFIED AT HIGHER LATITUDES WITH A MEAN MID-UPPER LEVEL  
TROUGH AND SURFACE LOW/STORM SOLUTION INTO ALASKA AND THE  
NORTHEAST PACIFIC. SLOW TRANSLATIONS LEADS TO AN INFRINGEMENT OF  
LEAD HEIGHT FALLS INTO WESTERN CANADA AND THE NORTHWEST U.S. ALONG  
WITH AN INCREASINGLY PRECIPITATION AMOUNT AND CHANCE OF MODERATE  
PRECIPITATION DAYS 5-7.  
 
RAPIDLY INCREASING FORECAST SPREAD LATER TUE INTO NEXT WED/THU IN  
A TRANSITIONING PATTERN DOWNSTREAM LOWERS FORECAST CONFIDENCE AND  
SUGGESTS PREFERENCE FOR AN ENSEMBLE MEAN BLEND AND CONTINUITY. IN  
THIS LATER TIME FRAME RECENT GFS RUNS BECOME MUCH LESS AMPLIFIED  
AND MORE PROGRESSIVE WITH NORTHERN STREAM FLOW ACROSS CANADA AND  
THE NORTHERN TIER OF THE LOWER 48 THAN THE ECMWF. I'D FAVOR  
DECENTLY AMPLIFIED FLOW INERTIA AND LEAN AT LEAST AS AMPLIFIED AS  
THE ENSEMBLE MEANS IF NOT QUITE THE ECMWF. AT THE SAME TIME,  
RECENT GFS RUNS ALSO BRING MUCH MORE ORGANIZED SOUTHERN STREAM  
ENERGY WITH ORIGIN FROM EAST PACIFIC TROPICAL ACTIVITY THAN OTHER  
GUIDANCE TO PRODUCE WIDESPREAD HEAVY PRECIPITATION WELL INLAND  
OVER THE SOUTHERN PLAINS IN STARK CONTRAST TO ALTERNATE GUIDANCE  
THAT HOLDS THE BULK OF PRECIPITATION MORE INTO THE LOWER  
MISSISSIPPI VALLEY AND IN GENERAL CLOSER TO THE COAST AND OFFSHORE  
INTO THE GULF OF MEXICO. THE GFS SEEMS WAY OVERDONE CONSIDERING  
LATEST NHC INPUT AND CONSIDERING THAT ANY TROPICAL SYSTEM INFLUNCE  
WOULD LIKELY BE MORE DISRUPTED MOVING INLAND OVER THE MOUTAINS OF  
MEXICO. WPC MEDIUM RANGE QPF FOCUSES A HEAVY RAINFALL THREAT OVER  
THE WESTERN THEN CENTRAL GULF COAST STATES. GUIDANCE IS IN BETTER  
AGREEMENT TO BRING MODEST PRECIPITATION ON THE BACKSIDE UP  
NORTHWARD THROUGH THE SOUTHERN AND CENTRAL ROCKY STATES WITH  
PROGRESSION OF A MAIN SOUTHERN STREAM TROUGH FROM CA/NW MEXICO.  
 
SCHICHTEL  
 
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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