769  
FXUS02 KWBC 301514  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1113 AM EDT SAT JUN 30 2018  
 
VALID 12Z TUE JUL 03 2018 - 12Z SAT JUL 07 2018  
 
...HOT TEMPERATURES TO GRADUALLY RETREAT WESTWARD OUT OF THE  
NORTHEAST LATER NEXT WEEK...  
 
   
..15 UTC UPDATE
 
 
MODELS/ENSEMBLE REMAIN CONSISTENT WITH THE PATTERN EVOLUTION  
ACROSS THE CONUS THROUGH THE MEDIUM RANGE, AND CHANGES TO THE  
FORECAST WERE RELATIVELY SMALL IN THIS UPDATE. A MULTI-MODEL BLEND  
INCLUDING THE 00Z ECMWF/UKMET/GFS WAS USED THROUGHOUT MUCH OF THE  
PERIOD, WITH MODESTLY INCREASED ENSEMBLE MEAN (00Z ECENS/NAEFS)  
WEIGHTING BY DAYS 6-7. MODELS HAVE TRENDED MORE AMPLIFIED WITH THE  
UPPER LOW OFF THE PACIFIC NORTHWEST FROM DAY 4 ONWARD, AND THE  
ECMWF HAS LAGGED THE GFS/UKMET ON THIS TREND. SOME QUESTION ALSO  
EXISTS AS TO THE DEGREE OF TROUGH AMPLIFICATION ACROSS THE  
NORTHEASTERN U.S. BY NEXT FRI-SAT, WITH THE GFS CONTINUING TO BE  
MORE AMPLIFIED THAN THE ECMWF. AT THIS TIME A COMPROMISE BETWEEN  
THE HIGHLY AMPLIFIED 00Z GFS AND THE LESS AMPLIFIED ECMWF IS  
PREFERRED.  
 
RYAN  
 
PREVIOUS DISCUSSION (ISSUED AT 0607 UTC)  
 
   
..OVERVIEW AND WEATHER THREATS/HIGHLIGHTS
 
 
WELL ABOVE AVERAGE TEMPERATURES (SOME RECORD BREAKING) OVER THE  
EASTERN GREAT LAKES/NORTHEAST/MID-ATLANTIC EARLY IN THE WEEK WILL  
TREND WESTWARD WITH TIME AS THE DOMINANT UPPER HIGH (HEAT DOME)  
MOVES SOUTHWESTWARD TOWARD THE ROCKIES BY NEXT SATURDAY.  
TEMPERATURES WELL INTO THE 90S WITH LOWS IN THE 70S (NEAR 80 IN  
THE URBAN CENTERS DC/PHILLY/NYC) WILL TREND BACK TOWARD NEAR OR  
JUST ABOVE CLIMO BY NEXT WEEKEND. PRECIPITATION WILL ROUND THE  
EDGES OF THE UPPER HIGH, FROM THE PACIFIC NORTHWEST TO THE HIGH  
PLAINS AND ALONG THE GULF COAST TO THE SOUTHEAST COAST. LOCALLY  
HEAVY RAIN WILL BE POSSIBLE WITH ORGANIZED THUNDERSTORM  
DEVELOPMENT TO THE NORTH AND WITH THE WEAKENING MID-LEVEL  
CIRCULATION OVER THE GULF COAST EARLY IN THE PERIOD (ESPECIALLY  
LOUISIANA INTO SOUTHEASTERN TEXAS).  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
LATEST MODEL/ENSEMBLE BLEND OFFERED A GOOD STARTING POINT -- 18Z  
GFS/GEFS AND 12Z ECMWF/CANADIAN/UKMET/ECMWF ENSEMBLE MEAN -- WITH  
A MAJORITY DETERMINISTIC WEIGHTING THROUGH THE PERIOD WITH GOOD OR  
BETTER THAN AVERAGE AGREEMENT. AROUND THE UPPER HIGH WILL BE A FEW  
UPPER LOWS -- OFF THE PACNW AND SOUTHEAST COAST AND ALONG THE GULF  
COAST -- WHICH WILL SPREAD PRECIPITATION ALONG/DOWNSTREAM OF THEIR  
TRACK. CONSENSUS TIMING/TRACK DIFFERENCES HAVE BEEN RELATIVELY  
SMALL BUT CONTINUE TO SHIFT AROUND WITH THE LATEST TREND TO BE  
QUICKER THROUGH CANADA AND THUS WITH THE COLD FRONT INTO THE GREAT  
LAKES/NORTHEAST NEXT THU-SAT. OFF THE SOUTHEAST COAST, TREND HAS  
GENERALLY BEEN FOR A MUCH WEAKER TROUGH, IF ANYTHING, TO APPROACH  
THE COAST LATE IN THE WEEK.  
 
FRACASSO  
 
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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