190  
FXUS02 KWBC 301559  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EDT TUE OCT 30 2018  
 
VALID 12Z FRI NOV 02 2018 - 12Z TUE NOV 06 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 RELATIVELY ACTIVE PERIOD  
OF WEATHER.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
MODELS ARE STILL STRUGGLING WITH THE WAVE OF LOW PRESSURE CROSSING  
THE EASTERN U.S. FRIDAY WITH THE GFS CONTINUING TO SHOW A SOMEWHAT  
WEAKER AND FASTER LOW PRESSURE SYSTEM AND THE ECMWF/UKMET THE  
SLOWER/STRONGER DETERMINISTIC SOLUTIONS (BUT WITH A FAIRLY  
SIGNIFICANT DEGREE OF ENSEMBLE SUPPORT). THOUGH A FAIRLY LARGE  
DEGREE OF VARIABILITY EXISTS OVER SEVERAL RUNS, THE ENSEMBLE TREND  
HAS BEEN DECIDEDLY SLOWER AND PREFERRED TO SIDE WITH THE ECMWF-LED  
CLUSTER (INCLUDING THE 00Z CANADIAN).  
 
FROM SUNDAY ONWARD, ENSEMBLE GUIDANCE SUGGESTS THAT THE UPPER  
RIDGING JUST OFF CALIFORNIA WILL TREND EASTWARD AND FLATTEN WHILE  
UPPER RIDGING IN THE NW ATLANTIC NEAR BERMUDA WILL TREND  
NORTHWESTWARD, FAVORING A CONTINUATION OF THE CENTRAL CONUS  
TROUGHING. THIS MAY ALSO HAVE THE EFFECT OF PREVENTING THE LEAD  
EASTERN SYSTEM FROM STAYING OFFSHORE AFTER THIS WEEKEND AS IT MAY  
BE SHUNTED BACK WESTWARD TOWARD THE COAST BEFORE WEAKENING. THE  
NORTH PACIFIC FLOW MAY BEGIN TO TREND TOWARD A MORE ZONAL PATTERN  
WHICH INTRODUCES MORE CHAOS INTO THE FORECAST, PARTICULARLY BY THE  
END OF THE EXTENDED PERIOD IN THE PAC NW INTO THE GULF OF ALASKA.  
BETTER AGREEMENT (THOUGH STILL WITH SPATIAL/STRENGTH DETAILS)  
EXISTS IN THE MID-MISSISSIPPI VALLEY AS A STRENGTHENING AREA OF  
LOW PRESSURE MAY LIFT TOWARD THE GREAT LAKES NEXT TUESDAY. ECMWF  
ENSEMBLE MEAN HAS LOWERED ITS PRESSURE ~4MB EACH CYCLE SINCE  
YESTERDAY WHILE THE GEFS MEAN HAS WAVERED DUE TO LARGER SPREAD IN  
ITS MEMBERS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
RAIN WILL BE ON ITS WAY OUT 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 AND WARM FRONT THROUGH NEW  
ENGLAND. 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 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  
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.  
 
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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page