989  
FXUS02 KWBC 261601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT TUE JUN 26 2018  
 
VALID 12Z FRI JUN 29 2018 - 12Z TUE JUL 03 2018  
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
MODEL GUIDANCE THIS MORNING CONTINUES TO FORECAST FOR A HEAT WAVE  
TO SPREAD EASTWARD FROM THE CENTRAL PLAINS INTO THE EAST COAST BY  
THIS WEEKEND WHILE GENERAL TROUGHING WILL KEEP CONDITIONS COOL  
OVER THE WESTERN U.S. MODEL AGREEMENT REMAINS GOOD REGARDING A  
BROAD UPPER-LEVEL TROUGH AND THE ASSOCIATED COLD FRONT MOVING OUT  
OF THE NORTHERN ROCKIES INTO THE NORTHERN PLAINS THROUGH DAY 5  
SUNDAY. THEREAFTER, MODELS BEGIN TO SHOW DIFFERENCES ON HOW AN  
UPPER-LEVEL CLOSED LOW OVER THE GULF OF ALASKA EVOLVES AS IT DROPS  
TOWARDS THE WEST COAST OF CANADA EARLY NEXT WEEK. THE ECMWF HAS  
BEEN THE FASTEST ON BRINGING CYCLONIC VORTICITY INLAND ACROSS  
BRITISH COLUMBIA TOWARD NORTHERN IDAHO ON DAY 7 TUESDAY WHILE THE  
GFS KEEPS THE CYCLONE CENTER FARTHER BACK ALONG THE COAST OF  
BRITISH COLUMBIA. THE ECMWF HAS SETTLED INTO THE FASTER SOLUTION  
FOR THE LAST COUPLE OF RUNS WHILE THE GFS CONTINUES TO SHOW  
INCONSISTENCY BETWEEN ITS DETERMINISTIC SOLUTIONS AND THE ENSEMBLE  
MEANS (I.E. THE GEFS). THE GEFS HAS BEEN COMPARABLE TO THE 00Z EC  
ENSEMBLE MEAN WITH A WEAKER SURFACE LOW CENTER AROUND ALBERTA  
CANADA ON DAY 7.  
 
THEREFORE, THE WPC MORNING PACKAGE WAS BASED ON A GENERAL  
COMPROMISE BETWEEN THE 06Z GFS/06Z GEFS AND THE 00Z ECMWF/00Z EC  
MEAN THROUGH DAY 5. MORE WEIGHTS WERE THEN GIVEN TO THE 00Z EC  
MEAN FOR DAY 6 AND 7, WITH 70% ASSIGNED TO THE 00Z EC/EC MEAN ON  
DAY 7.  
 
   
..WEATHER THREATS/HIGHLIGHTS
 
 
LOW PRESSURE TRACKING NORTHEAST FROM THE PLAINS INTO CANADA FROM  
FRI ONWARD ALONG WITH ITS ASSOCIATED FRONTS AND UPPER SHORTWAVE  
SUPPORT WILL LIKELY PRODUCE CONVECTIVE EPISODES CAPABLE OF  
PRODUCING AREAS OF HEAVY RAINFALL. BEST SIGNAL FOR HIGHEST TOTALS  
IS ACROSS THE NORTHERN PLAINS/MIDWEST/UPPER MS VALLEY/UPPER GREAT  
LAKES. SOUTHWARD PROGRESSION OF THE COLD FRONT MAY BRING  
CONVECTION INTO THE CENTRAL PLAINS. SOME ACTIVITY MAY BE STRONG  
TO SEVERE AS WELL. CHECK LATEST SPC OUTLOOKS AS DETAILS BECOME  
MORE CLEAR IN COMING DAYS. EXPECT SHOWERS/THUNDERSTORMS TO EXTEND  
FARTHER EASTWARD LATER IN THE PERIOD BUT LIKELY WITH LESSER  
AMOUNTS AS BEST UPPER DYNAMICS LIFT INTO CANADA. MEANWHILE THERE  
SHOULD BE DIURNALLY FAVORED CONVECTION OVER PORTIONS OF THE  
SOUTH/FLORIDA THROUGH THE PERIOD WITH SOME LOCALLY HEAVY AMOUNTS.  
IT REMAINS A QUESTION MARK TO WHAT EXTENT UPPER ENERGY/SURFACE  
FEATURE(S) FLOWING AROUND THE DEEP LAYER HIGH TO THE NORTH MAY  
ENHANCE THIS CONVECTION.  
 
A HEAT WAVE IS EXPECTED TO SPREAD INTO THE EASTERN U.S. THIS  
WEEKEND AND ONLY DAMPENED A BIT EARLY NEXT WEEK WITH A BETTER  
CHANCE OF SHOWERS AND THUNDERSTORMS. WITHIN THE LARGE AREA OF HOT  
AND HUMID WEATHER OVER THE CENTRAL/EASTERN U.S., HIGHEST MIN/MAX  
TEMPERATURE ANOMALIES OF PLUS 10-20F SHOULD EXTEND FROM THE  
MIDWEST THROUGH THE GREAT LAKES/OHIO VALLEY AND NORTHEAST. THE  
HEAT/HUMIDITY WILL GRADUALLY ERODE FROM THE WEST OVER THE COURSE  
OF THE PERIOD AS A PLAINS COLD FRONT MOVES INTO THE GREAT LAKES.  
THERE ARE MANY LOCATIONS THAT MAY SEE ONE OR MORE DAYS OF MIN  
TEMPS AT LEAST CLOSE TO DAILY RECORD WARM VALUES. DAILY RECORD  
HIGHS SHOULD BE LESS NUMEROUS AND MOST LIKELY CONFINED TO THE  
GREAT LAKES/OHIO VALLEY/NORTHEAST DURING SAT-MON. THE HUMIDITY  
WILL CONTRIBUTE TO HIGH HEAT INDEX VALUES. BELOW NORMAL  
TEMPERATURES WILL BE MOST COMMON OVER THE WEST AND HIGH PLAINS,  
WITH THE NORTHERN ROCKIES/HIGH PLAINS LIKELY TO SEE ONE OR MORE  
DAYS OF HIGHS 10F OR MORE BELOW NORMAL FRI-SUN. EJECTION OF THE  
INITIAL WESTERN TROUGH ALOFT WILL HELP READINGS TREND TO  
MODERATELY ABOVE NORMAL LEVELS OVER THE CENTRAL/SOUTHERN PARTS OF  
THE WEST BY EARLY NEXT WEEK.  
 
KONG/RAUSCH  
 
WPC MEDIUM RANGE FORECASTS OF 500 MB HEIGHTS, SURFACE SYSTEMS,  
WEATHER GRIDS, QUANTITATIVE PRECIPITATION, AND WINTER WEATHER  
OUTLOOK PROBABILITIES 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  
 

 
 
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