767  
FXUS02 KWBC 300531  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
130 AM EDT TUE OCT 30 2018  
 
VALID 12Z FRI NOV 02 2018 - 12Z TUE NOV 06 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
A MEAN UPPER-LEVEL TROUGH IS EXPECTED TO PERSIST ACROSS THE  
CENTRAL U.S. THROUGH THE EXTENDED PERIOD. THE TROUGH WILL BE  
REINFORCED BY A SERIES OF SHORTWAVES ORIGINATING IN THE NORTH  
PACIFIC, POTENTIALLY INTERACTING WITH ADDITIONAL SHORTWAVE ENERGY  
OF POLAR/ARCTIC ORIGIN AS THEY CROSS THE CANADIAN ROCKIES BEFORE  
AMPLIFYING AS THEY ENCOUNTER THE AREA OF BROAD AND PERSISTENT  
CYCLONIC FLOW ACROSS THE CENTRAL U.S. A SERIES OF FRONTAL/LOW  
PRESSURE SYSTEMS WILL ACCOMPANY THESE SHORTWAVES ACROSS THE CONUS,  
GENERALLY 1-2 DAYS APART, RESULTING IN A RELATIVELY ACTIVE PERIOD  
OF WEATHER.  
 
MODELS ARE STILL STRUGGLING WITH THE WAVE OF LOW PRESSURE CROSSING  
THE EASTERN U.S. ON WHAT IS NOW DAY 3 (FRI), WITH THE GFS  
CONTINUING TO SHOW A SOMEWHAT WEAKER AND FASTER LOW PRESSURE  
SYSTEM AND THE ECMWF THE SLOWEST/STRONGEST SOLUTION (WITH A FAIRLY  
SIGNIFICANT DEGREE OF ENSEMBLE SUPPORT). DETERMINISTIC SOLUTIONS  
HAVE STILL SHOWN A FAIRLY LARGE DEGREE OF VARIABILITY LOOKING BACK  
SEVERAL RUNS, SO BELIEVE THAT A COMPROMISE APPROACH BETWEEN THE  
TWO EXTREMES IS STILL BEST. EVEN A COMPROMISE, HOWEVER, WILL  
RESULT IN A SIGNIFICANT SLOWDOWN OF THE SURFACE LOW COMPARED TO  
CONTINUITY. ADDITIONAL SHORTWAVE ENERGY AND AN ASSOCIATED SURFACE  
LOW WILL CROSS THE CENTRAL PLAINS/MISSISSIPPI VALLEY ON DAY 3,  
WITH YET ANOTHER ENTERING THE NORTHERN PLAINS BY THE WEEKEND, BUT  
MODEL SOLUTIONS FOR THESE SYSTEMS ARE CLOSER ON TIMING AND  
INTENSITY. GIVEN THESE CONSIDERATIONS, A MULTI-MODEL DETERMINISTIC  
BLEND (INCLUDING THE ECMWF/GFS/UKMET) WAS USED AS A BASIS FOR THE  
WPC FORECAST DURING DAYS 3-5.  
 
BY NEXT MON-TUE (DAYS 6-7), MODEL SPREAD CONTINUES TO QUICKLY  
INCREASE. ENSEMBLE GUIDANCE SUGGESTS THAT THE AMPLIFIED AND BLOCKY  
FLOW PREVALENT ACROSS THE NORTH PACIFIC EARLY IN THE PERIOD MAY  
BEGIN TO TREND TOWARD A MORE ZONAL PATTERN, WHICH INTRODUCES MORE  
CHAOS INTO THE FORECAST, PARTICULARLY BY THE END OF THE EXTENDED  
PERIOD. NONETHELESS, THE CENTRAL U.S. TROUGH APPEARS LIKELY TO  
PERSIST FOR AT LEAST A BIT LONGER, WITH THE ARRIVAL OF ADDITIONAL  
SHORTWAVE ENERGY CONTINUING TO LOWER HEIGHTS BY TUE. MODEL  
SOLUTIONS DIFFER QUITE SUBSTANTIALLY, HOWEVER, WITH RESPECT TO THE  
TIMING AND AMPLITUDE OF THIS FEATURE ALONG WITH ANOTHER WAVE  
NEARING THE PACIFIC NORTHWEST BY THIS TIME. AS A RESULT,  
SUBSTANTIAL WEIGHT WAS PLACED TOWARD THE ECENS AND GEFS ENSEMBLE  
MEANS DURING THE DAY 6-7 TIME PERIOD.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
RAIN MAY BE ONGOING AT THE BEGINNING OF THE EXTENDED PERIOD ON FRI  
ACROSS MUCH OF THE EASTERN U.S. IN ASSOCIATION WITH A LOW PRESSURE  
SYSTEM/COLD FRONT. THE MISSISSIPPI VALLEY WILL SEE THE POTENTIAL  
FOR RAIN TO BECOME MORE WIDESPREAD LATE IN THE WEEKEND INTO EARLY  
NEXT WEEK AS A COUPLE FRONTAL SYSTEMS TRAVERSE THE REGION AND TAP  
INTO GULF OF MEXICO MOISTURE. HEAVY RAIN WILL BE POSSIBLE ACROSS  
THE PACIFIC NORTHWEST THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK  
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 THE WEEKEND  
ACROSS MUCH OF THE CENTRAL U.S. AND PORTIONS OF THE EASTERN 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 THROUGH THE WEEKEND AND INTO EARLY NEXT WEEK.  
 
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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