109  
FXUS02 KWBC 140451  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1250 AM EDT SAT JUL 14 2018  
 
VALID 12Z TUE JUL 17 2018 - 12Z SAT JUL 21 2018  
   
..OVERVIEW
 
 
THE FLOW PATTERN ACROSS THE CONTIGUOUS U.S. WILL BECOME A BIT MORE  
AMPLIFIED DURING THE MEDIUM RANGE PERIOD WITH AN UPPER-LEVEL RIDGE  
EXPANDING FROM THE GREAT BASIN TO THE SOUTHERN ROCKIES, AND A  
SERIES OF UPPER WAVES GRADUALLY CARVING OUT A TROUGH ACROSS THE  
GREAT LAKES. HEIGHTS ARE ALSO EXPECTED TO FALL ACROSS THE PACIFIC  
NORTHWEST BY LATE NEXT WEEK AS AN UPPER LOW DIGS SOUTH FROM THE  
GULF OF ALASKA TOWARD THE REGION.  
 
   
..GUIDANCE EVALUATION AND PREFERENCES
 
 
A MAJORITY DETERMINISTIC BLEND INCLUDING THE ECMWF/GFS/CMC WAS  
INITIALLY PREFERRED DURING DAYS 3-5 (TUE-THU). MODELS HAVE SETTLED  
TOWARD A SOMEWHAT SLOWER/MORE AMPLIFIED SOLUTION WITH THE  
TROUGH/UPPER LOW PASSING SOUTH OF HUDSON BAY AND MOVING EAST INTO  
QUEBEC DURING THIS TIME FRAME. THE SAME GENERALLY HOLDS TRUE FOR  
ADDITIONAL SHORTWAVE ENERGY CROSSING THE NORTH CENTRAL U.S.  
WED-THU, WHICH THEN LOOKS LIKELY TO AMPLIFY FURTHER ACROSS THE  
GREAT LAKES/OHIO VALLEY FRI-SAT. FARTHER WEST, MODELS CONTINUE TO  
SHOW A COMPACT BUT ENERGETIC SHORTWAVE DIVING SOUTHEAST ACROSS THE  
GULF OF ALASKA TOWARD BRITISH COLUMBIA TUE-WED, WITH HEIGHTS  
FALLING ACROSS THE U.S. PACIFIC NORTHWEST BY LATER IN THE WEEK.  
SOME TIMING DIFFERENCES REMAIN, BUT IN GENERAL GUIDANCE HAS  
TRENDED TOWARD SOMEWHAT SLOWER/MORE AMPLIFIED SOLUTIONS HERE AS  
WELL. GIVEN THE INCREASE IN SPREAD, MAJORITY WEIGHTING WAS SHIFTED  
TO ENSEMBLE MEANS FOR DAYS 6-7 (FRI-SAT), INCLUDING THE ECENS AND  
NAEFS MEANS.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
SHOWERS AND STORMS WITH LOCALLY HEAVY RAIN WILL ACCOMPANY A COLD  
FRONT FROM THE APPALACHIANS TO THE  
SOUTHEAST/MID-ATLANTIC/NORTHEAST TUE-WED. THE TRAILING END OF THE  
FRONTAL BOUNDARY IS EXPECTED TO STALL FROM THE SOUTHEAST TO THE  
SOUTHERN/CENTRAL PLAINS, WHICH COULD ALSO FOCUS LOCALLY HEAVY  
SHOWERS AND THUNDERSTORMS THROUGH LATER NEXT WEEK. MONSOONAL  
MOISTURE WILL ALSO PRODUCE SCATTERED AFTERNOON/EVENING  
THUNDERSTORMS FROM THE SOUTHERN GREAT BASIN/SOUTHWEST TO THE  
SOUTHERN/CENTRAL ROCKIES THROUGH THE NEXT WEEK, WITH LOCALLY HEAVY  
RAIN POSSIBLE ESPECIALLY EARLY IN THE WEEK (THE BUILDING  
UPPER-LEVEL RIDGE SHOULD GRADUALLY REDUCE THE COVERAGE OF  
CONVECTION BY LATER NEXT WEEK).  
 
IN THE WAKE OF THE COLD FRONT, HIGH TEMPERATURES ARE EXPECTED TO  
BE 5 TO 10 DEG BELOW AVERAGE ACROSS THE CENTRAL/NORTHERN PLAINS  
AND PORTIONS OF THE MIDWEST/GREAT LAKES THROUGH MUCH OF NEXT WEEK.  
HOT TEMPERATURES ACROSS THE PACIFIC NORTHWEST (HIGHS 5 TO 10 DEG  
ABOVE AVERAGE) SHOULD MODERATE SOME BY LATER NEXT WEEK AS A  
PACIFIC COLD FRONT MOVES INLAND.  
 
RYAN  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND AT:  
 
HTTP://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTP://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTP://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTP://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTP://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTP://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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