655  
FXUS02 KWBC 310632  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
231 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 GFS  
AND THE 12Z ECMWF UKMET. THIS BLEND YIELDED FAVORABLE RESULTS  
ELSEWHERE AS WELL, WITH THE NEXT WEAKENING LOW PRESSURE SYSTEM  
EXITING THE ROCKIES INTO THE PLAINS ON DAYS 3-4. BY DAY 5 (MON),  
THE NEXT SHORTWAVE SHOULD BE EXITING FROM THE ROCKIES INTO THE  
PLAINS, WITH YET ANOTHER SURFACE LOW PRESSURE SYSTEM DEVELOPING.  
MODEL SPREAD BEGINS TO INCREASE FOR THIS SYSTEM AS IT CROSSES THE  
PLAINS AND ESPECIALLY BY DAYS 6-7 (TUE-WED) AS SOME SOLUTIONS SPIN  
UP AN INTENSE LOW PRESSURE SYSTEM ACROSS THE MIDWEST/GREAT LAKES.  
MODEL SOLUTIONS SHOW SPREAD WITH RESPECT TO BOTH TIMING AND  
AMPLITUDE OF THIS SYSTEM, BUT THERE IS BROAD AGREEMENT THAN THE  
WAVE WILL REACH THE PLAINS AND AMPLIFY TO SOME DEGREE DURING THIS  
TIME PERIOD. AS A RESULT, USE OF DETERMINISTIC GUIDANCE WAS  
GRADUALLY TAPERED DURING THE DAY 5-7 TIME FRAME, WITH USE OF ECENS  
AND GEFS ENSEMBLE MEANS GRADUALLY INCREASED.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
A LOW PRESSURE SYSTEM AND THE ASSOCIATED RAIN WILL BE THE WAY OUT  
AT THE BEGINNING OF THE EXTENDED PERIOD ON SAT 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. 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 PERHAPS THE 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.  
 
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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