114  
FXUS02 KWBC 011554  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1154 AM EDT THU NOV 01 2018  
 
VALID 12Z SUN NOV 04 2018 - 12Z THU NOV 08 2018  
   
..PATTERN OVERVIEW
 
 
BROAD CYCLONIC FLOW AND UPPER-LEVEL TROUGHING IS FORECAST FOR THE  
CENTRAL US NEXT WEEK AS UPPER RIDGING IN THE ATLANTIC HOLDS IN  
PLACE. THE TROUGH WILL BE REINFORCED BY A SERIES OF SHORTWAVES  
ORIGINATING IN THE NORTH PACIFIC (NORTH OF ANOTHER PERSISTENT  
UPPER-LEVEL RIDGE), POTENTIALLY INTERACTING WITH ADDITIONAL  
SHORTWAVE ENERGY OF POLAR/ARCTIC ORIGIN AS THEY CROSS THE CANADIAN  
ROCKIES BEFORE AMPLIFYING IN THE PLAINS. A DEEPENING AREA OF LOW  
PRESSURE IS EXPECTED TO LIFT INTO THE GREAT LAKES NEXT TUESDAY  
WHICH WILL BRING IN ANOTHER SHOT OF COOLER CANADIAN AIR.  
 
   
..GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE RECENT GFS RUNS DIVERGED FROM THE CONSENSUS OVER THE SOUTHERN  
PLAINS LATE THIS WEEKEND AS A LEAD SYSTEM WEAKENS AND LIFTS  
NORTHWARD INTO THE LAKES. THE CONSENSUS TAKES ONE SHORTWAVE TO THE  
NORTHEAST WHILE THE GFS HAD SEPARATED THE TROUGH INTO A  
NORTHERN/SOUTHERN PORTION WHICH WAS NOT SHOWN IN THE ENSEMBLES  
(EXCEPT FOR SEVERAL GEFS MEMBERS) NOR HAS BEEN SHOWN IN PREVIOUS  
RUNS. OPTED TO RELY ON THE ECMWF-LED CONSENSUS WITH THE  
CANADIAN/UKMET AND THE ECMWF ENSEMBLE MEAN (ALONG WITH THE  
PREVIOUS FORECAST).  
 
BY MONDAY THE NEXT SHORTWAVE SHOULD BE EXITING THE ROCKIES INTO  
THE PLAINS, WITH DEVELOPMENT OF YET ANOTHER SURFACE LOW PRESSURE  
SYSTEM EXPECTED. SPREAD AMONG THE DETERMINISTIC GUIDANCE SEEMS TO  
HAVE INCREASED RATHER SUBSTANTIALLY WITH THIS SECOND SYSTEM BY DAY  
5 (TUE) AND ONWARD, PARTIALLY STEMMING FROM THE GFS BUT ALSO FROM  
HOW THE MODELS/ENSEMBLES HANDLE INCOMING PACIFIC SHORTWAVES INTO  
THE QUICK NW FLOW. PREFERRED THE MORE STABLE SOLUTIONS NEAR THE  
ECMWF ENSEMBLE MEAN AND EVEN GEFS MEAN WHICH ALIGN WITH THE 00Z  
ECMWF. THIS ALSO KEEPS REASONABLY GOOD CONTINUITY WITH THE  
PREVIOUS FORECAST. THIS SCENARIO SHOWS A STRENGTHENING SURFACE LOW  
MOVING NORTH-NORTHEASTWARD ACROSS THE GREAT LAKES ON TUE AND  
CONTINUING TO DEEPEN (PERHAPS QUITE SUBSTANTIALLY) AS THE LOW  
MOVES INTO EASTERN ONTARIO TOWARD JAMES BAY ON DAY 6 (WED).  
 
LATER IN THE FORECAST PERIOD (NEXT WED-THU), ADDITIONAL MOSTLY  
NORTHERN STREAM SHORTWAVES WILL CONTINUE TO REINFORCE THE MEAN  
TROUGH (ALTHOUGH THE DETAILS OF THESE SYSTEMS ARE QUITE MURKY).  
COLD AIR ACROSS THE LAKES COULD SUPPORT LAKE-ENHANCED/EFFECT SNOW  
(OR RAIN/SNOW MIX). THE NEXT PACIFIC SYSTEM MAY STAY JUST OFFSHORE  
BRITISH COLUMBIA BUT SPREAD SOME LIGHTER RAIN/SNOW INTO ESPECIALLY  
COASTAL AREAS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
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 AN INCH  
OR MORE OF RAIN POSSIBLE OVER A LARGE AREA, PARTICULARLY OVER THE  
OHIO/TENNESSEE VALLEYS NORTHWARD TO THE LOWER GREAT LAKES. OFF THE  
COAST, THE LINGERING STATIONARY FRONT MAY PUSH BACK TOWARD THE  
COAST AND BRING THE POTENTIAL FOR PRECIPITATION BACK TO THE I-95  
CORRIDOR FROM THE SOUTHEAST ALL THE WAY NORTHWARD TO NEW ENGLAND.  
HEAVY RAIN AND HIGHER ELEVATION SNOW WILL BE POSSIBLE ACROSS THE  
PACIFIC NORTHWEST 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 EARLY NEXT WEEK. CHILLY  
CONDITIONS WILL BE PREVALENT ACROSS PORTIONS OF THE CENTRAL U.S.  
BENEATH THE PERSISTENT UPPER TROUGH, WHERE HIGHS WILL GENERALLY BE  
5 TO 10 DEG F BELOW AVERAGE. CHILLY AIR MAY MAKE ITS WAY INTO THE  
EASTERN U.S. BY LATER NEXT WEEK BEHIND A STRONG COLD FRONT BUT  
WILL MOSTLY BE FOCUSED WEST OF THE APPALACHIANS UNTIL THEN. AHEAD  
OF THE FRONT, TEMPERATURES WILL RISE TO ABOVE AVERAGE BY 5-10 DEG  
F ON TUESDAY. MEANWHILE, ABOVE AVERAGE TEMPERATURES WILL PERSIST  
ACROSS PORTIONS OF THE WEST, FROM CALIFORNIA INTO THE GREAT BASIN  
(ESPECIALLY SUN-TUE), WHERE HIGH TEMPERATURES MAY REACH 5 TO 15  
DEG F ABOVE AVERAGE DOWNSTREAM OF PERSISTENT UPPER-LEVEL RIDGING.  
 
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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