225  
FXUS02 KWBC 271600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT WED JUN 27 2018  
 
VALID 12Z SAT JUN 30 2018 - 12Z WED JUL 04 2018  
   
..OVERVIEW AND GUIDANCE EVALUATION/PREFERENCES
 
 
MODEL GUIDANCE THIS MORNING SHOWS EXCELLENT AGREEMENT WITH THE  
OVERALL EVOLUTION OF THE SYNOPTIC PATTERN ACROSS THE U.S. THROUGH  
NEXT WEDNESDAY. A WARM SUBTROPICAL HIGH WILL LIKELY BECOME FIRMLY  
ESTABLISHED FROM THE CENTRAL U.S. INTO THE EAST COAST THIS  
WEEKEND, SIGNALING THE BEGINNING OF A HEAT WAVE. MEANWHILE, A  
BROAD UPPER-LEVEL TROUGH SLOWLY LIFTING OUT OF THE NORTHERN PLAINS  
WILL BE FOLLOWED BY THE APPROACH OF A CLOSED LOW FORECAST TO DROP  
SOUTHEASTWARD FROM THE GULF OF ALASKA TOWARD THE PACIFIC NORTHWEST  
BY THE MIDDLE OF NEXT WEEK. THE GFS SOLUTIONS HAVE TRENDED FASTER  
TOWARD THE ECMWF REGARDING THIS CLOSED LOW, AND THEY BOTH MODELS  
AGREE THAT A POSITIVELY TILTED TROUGH PATTERN WITH A VORTICITY  
CENTER WILL REACH THE PACIFIC NORTHWEST COAST BY DAY 7 WEDNESDAY.  
FARTHER EAST, AS THE SUBTROPICAL HIGH BECOMES FIRMLY ESTABLISHED  
EARLY NEXT WEEK, SOME WESTWARD-MOVING DISTURBANCES ARE FORECAST TO  
MOVE ACROSS FLORIDA INTO THE GULF COAST. OVER THE WESTERN  
ATLANTIC, MODELS HAVE BEEN SUGGESTING THE DEVELOPMENT OF A  
CYCLONIC CIRCULATION SOUTH OF THE SUBTROPICAL HIGH. THE DIFFUSE  
NATURE OF THIS FEATURE LENDS ITSELF TO LOW PREDICTABILITY FOR  
SPECIFICS. HOWEVER, THE LATEST GUIDANCE SHOWS A TENDENCY FOR THIS  
FEATURE TO FORM FARTHER SOUTH NEAR BERMUDA SUNDAY INTO MONDAY  
BEFORE TURNING WESTWARD BY MIDWEEK NEXT WEEK.  
 
WITH THE ABOVE CONSIDERATIONS, THE WPC MORNING GRID PACKAGE WAS A  
CONSENSUS BETWEEN THE 00Z ECMWF AND THE 06Z GFS, TRENDING 70  
PERCENT TOWARD THEIR ENSEMBLE MEANS FOR DAYS 6 AND 7.  
 
   
..WEATHER THREATS/HIGHLIGHTS
 
 
EXPECT POTENTIAL FOR SOME HEAVY/STRONG CONVECTION BETWEEN THE  
UPPER GREAT LAKES AND CENTRAL PLAINS EARLY IN THE PERIOD, IN  
ASSOCIATION WITH A COLD FRONT INITIALLY NEAR THIS AREA.  
PROGRESSION OF THE FRONT WILL EVENTUALLY BRING  
SHOWERS/THUNDERSTORMS INTO THE EAST BUT WITH ANY HEAVY ACTIVITY  
TENDING TO BE MORE LOCALIZED AS THE BEST DYNAMICS LIFT INTO CANADA  
AFTER THE WEEKEND. THE TRAILING PART OF THE FRONT WILL STALL OVER  
THE PLAINS AND LIFT BACK AS A WARM FRONT SO THERE WILL BE  
POTENTIAL FOR ADDITIONAL RAINFALL OVER PORTIONS OF THE CENTRAL  
U.S. AFTER THE MORE CONCENTRATED ACTIVITY DURING THE WEEKEND. THE  
OTHER AREA OF FOCUS FOR HEAVY RAINFALL POTENTIAL WILL BE OVER THE  
GULF COAST/FLORIDA, WITH THE COMBINATION OF UPPER LEVEL ENERGY AND  
SURFACE TROUGHING CONTRIBUTING TO ACTIVITY.  
 
IN TERMS OF HIGHEST TEMPERATURE ANOMALIES, THE CORE OF THE HEAT  
WAVE AFFECTING THE EASTERN HALF OF THE U.S. SHOULD EXTEND FROM THE  
MIDWEST/GREAT LAKES INTO THE NORTHEAST. THE GREATEST COVERAGE OF  
PLUS 10-20F ABOVE NORMAL READINGS WILL LIKELY EXIST SAT-MON,  
FOLLOWED BY GRADUAL MODERATION AS THE PLAINS FRONT APPROACHES.  
BEST POTENTIAL FOR RECORD HIGHS WILL BE FROM THE LOWER GREAT  
LAKES/UPPER OHIO VALLEY INTO THE NORTHERN MID ATLANTIC/NORTHEAST  
SAT-SUN WHILE BROADER COVERAGE OF RECORD WARM LOWS IS POSSIBLE  
SAT-MON. THE NORTHERN ROCKIES/HIGH PLAINS WILL SEE BELOW NORMAL  
HIGHS DURING THE WEEKEND FOLLOWED BY A TREND TOWARD NEAR NORMAL  
TEMPERATURES. THE EVOLVING PATTERN BY LATE IN THE PERIOD WILL  
TEND TO SUPPORT MODERATELY BELOW NORMAL TEMPERATURES ALONG THE  
WEST COAST AND OVER THE NORTHWEST TOWARD MIDWEEK.  
 
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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