112  
FXUS02 KWBC 311554  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1153 AM EDT WED OCT 31 2018  
 
VALID 12Z SAT NOV 03 2018 - 12Z WED NOV 07 2018  
   
..PATTERN OVERVIEW
 
 
A MEAN UPPER-LEVEL TROUGH IS EXPECTED TO PERSIST AND RELOAD 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 PERIOD OF RELATIVELY  
ACTIVE WEATHER.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODEL CONSENSUS HAS IMPROVED A BIT WITH RESPECT TO THE LOW  
PRESSURE SYSTEM EXPECTED TO CROSS THE NORTHEASTERN U.S. ON DAY 3  
(SAT), ALTHOUGH SPREAD REMAINS A BIT HIGHER THAN AVERAGE FOR DAY  
3, AS THIS SYSTEM HAS CONTINUED TO PROVE RATHER DIFFICULT FOR  
FORECAST MODELS TO GET A HANDLE ON. A CLUSTERING OF SOLUTIONS  
AROUND THE ECENS/GEFS MEANS WAS FAVORED, WHICH INCLUDED THE RECENT  
GFS/ECMWF/UKMET/CANADIAN. THIS BLEND YIELDED FAVORABLE RESULTS  
ELSEWHERE AS WELL, WITH THE NEXT WEAKENING LOW PRESSURE SYSTEM  
EXITING THE ROCKIES INTO THE PLAINS THIS WEEKEND. BY MONDAY, THE  
NEXT SHORTWAVE SHOULD BE EXITING FROM THE ROCKIES INTO THE PLAINS,  
WITH YET ANOTHER SURFACE LOW PRESSURE SYSTEM DEVELOPING. ENSEMBLE  
MEANS CONTINUE TO TREND STRONGER AND FARTHER SOUTH, LED BY THE  
DETERMINISTIC SOLUTIONS THOUGH SOME SPIN UP AN INTENSE LOW  
PRESSURE SYSTEM ACROSS THE UPPER MIDWEST/GREAT LAKES. WITH SPREAD  
IN BOTH TIMING AND AMPLITUDE OF THIS SYSTEM, OPTED TO RELY ON A  
BLEND OF THE 06Z GFS/GEFS AND 00Z ECMWF/ECMWF ENSEMBLE MEAN WITH  
THE PREVIOUS FORECAST WHICH YIELDS A MODERATE CENTRAL PRESSURE IN  
THE 990S MB. THIS HAS THE POTENTIAL TO BE A DEEPER SYSTEM WITH  
MORE WIND/RAIN AND MAYBE SOME SNOW ON THE NW SIDE.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
A LOW PRESSURE SYSTEM AND THE ASSOCIATED RAIN WILL BE ON THE WAY  
OUT AT THE BEGINNING OF THE EXTENDED PERIOD ON SATURDAY ACROSS  
MUCH OF THE NORTHEASTERN U.S. THE MISSISSIPPI AND OHIO VALLEYS  
WILL SEE THE POTENTIAL FOR RAIN TO BECOME MORE WIDESPREAD LATE IN  
THE WEEKEND INTO NEXT WEEK AS A COUPLE FRONTAL SYSTEMS TRAVERSE  
THE REGION AND TAP INTO GULF OF MEXICO MOISTURE. AN EXPANDING  
AREAS OF RAIN WILL SPREAD NORTHEASTWARD AHEAD OF THE MIDWEEK  
SYSTEM (TUE-WED) WITH MORE THAN AN INCH OR SO OF RAIN OVER A LARGE  
AREA, PARTICULARLY OVER THE OHIO/TENNESSEE VALLEYS NORTHWARD TO  
MICHIGAN. OFF THE COAST, THE LINGERING STATIONARY FRONT MAY PUSH  
BACK TOWARD THE COAST AND BRING ANOTHER AREA OF RAIN INTO THE  
NORTHEAST. HEAVY RAIN AND HIGHER ELEVATION SNOW 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 THEN  
CENTRAL ROCKIES BY NEXT WEEK AS SNOW LEVELS LOWER. CHILLY  
CONDITIONS WILL BE PREVALENT THROUGH THE WEEKEND ACROSS PORTIONS  
OF THE CENTRAL AND 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 INTO NEXT WEEK  
DOWNSTREAM OF A PERSISTENT UPPER-LEVEL RIDGE OFFSHORE.  
 
FRACASSO/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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