900  
FXUS02 KWBC 291601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT SUN JUL 29 2018  
 
VALID 12Z WED AUG 01 2018 - 12Z SUN AUG 05 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
MODEL GUIDANCE THIS MORNING SHOWS DECENT AGREEMENT ON THE SYNOPTIC  
PATTERN EVOLUTION ACROSS THE U.S. THROUGH NEXT WEEKEND. AN  
UPPER-LEVEL TROUGH MOVING TOWARD THE EASTERN U.S. WILL BE IMPEDED  
AND THEN WEAKENED BY A STRONG BERMUDA HIGH WHICH IS FORECAST TO  
REMAIN A DOMINATE FEATURE FROM THE WESTERN ATLANTIC TO THE EAST  
COAST THROUGH MUCH OF THIS WEEK. THIS WILL ENSURE TROPICAL  
MOISTURE TO MOVE UP THE EAST COAST WITH A GOOD CHANCE OF  
PRECIPITATION. MEANWHILE, MODELS CONTINUE TO SHOW NOTICEABLE  
DIFFERENCES ON THE STRENGTH OF A COOL AIRMASS MOVING INTO THE  
NORTHERN PLAINS AND THE GREAT LAKES DURING THE MIDDLE OF THE WEEK,  
WITH THE ECMWF CONTINUES TO OFFER THE WARMEST SOLUTION WHILE THE  
GFS SOLUTIONS REMAIN RATHER COOL. THIS IS REFLECTED BY A STRONGER  
HIGH PRESSURE SYSTEM SHOWN IN THE LATEST GFS (06Z) ALTHOUGH NOT AS  
STRONG AS IN PREVIOUS RUNS. BY NEXT WEEKEND, MODELS AGREE THAT  
THE BERMUDA HIGH WILL ERODE MUCH OF THE UPPER TROUGH AXIS ALONG  
THE MISSISSIPPI VALLEY WITH MOISTURE LINGERING ALONG THE EAST  
COAST. MEANWHILE, A SIGNIFICANT UPPER TROUGH/CLOSED LOW WOULD  
DROP SOUTHEASTWARD ACROSS THE GULF OF ALASKA TOWARD THE PACIFIC  
NORTHWEST. TELECONNECTIONS RELATIVE TO THE POSITIVE HEIGHT  
ANOMALY CENTER NEAR THE ALEUTIANS IN D+8 CHARTS FAVOR A  
NORTHEASTERN PACIFIC TROUGH CLOSER TO THE ECMWF/ECMWF MEAN.  
THEREFORE, THE WPC MORNING GRID FIELDS WERE DERIVED USING A  
GENERAL COMPROMISE OF THE 00Z ECMWF WITH THE 06Z GFS THROUGH DAY 5  
FRIDAY. FOR DAY 6 AND 7, A 60% OF THE 00Z ECMWF/EC MEAN WAS  
BLENDED WITH 40% OF THE 06Z GFS/GEFS MEAN.  
 
KONG  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE SOUTHEAST CONTINUES TO SHOW THE BEST POTENTIAL FOR HIGHEST  
RAINFALL TOTALS DURING THE PERIOD. FLOW AROUND THE BERMUDA HIGH  
WILL SUPPORT A PERSISTENT FEED OF LOW LEVEL ATLANTIC/EASTERN GULF  
MOISTURE INTO THE REGION. THIS MOISTURE SHOULD INTERACT WITH THE  
SLOW MOVING FRONT OVER THE EAST DURING THE FIRST HALF OF THE  
PERIOD. AFTER THE FRONT DISSIPATES EXPECT CONVECTION TO BE  
SOMEWHAT LESS ORGANIZED WITH INCREASING FOCUS ALONG TERRAIN AND  
LOCALIZED BOUNDARIES. CONVECTION/RAINFALL THROUGH THE PERIOD MAY  
BE PROBLEMATIC OVER AREAS THAT HAVE RECEIVED SIGNIFICANT RAINFALL  
OVER THE PAST TWO WEEKS. EXPECT SOME MOISTURE/RAINFALL TO EXTEND  
INTO THE MID-ATLANTIC/NORTHEAST, WITH POCKETS OF MODERATE-HEAVY  
ACTIVITY BUT IN GENERAL LESS EXTREME TOTALS THAN OVER THE  
SOUTHEAST.  
 
PERIODS OF CONVECTION WITH VARYING INTENSITY WILL CONTINUE OVER  
THE FOUR CORNERS STATES WITH SHOWERS/STORMS POSSIBLY EXTENDING  
INTO THE SOUTHERN HIGH PLAINS AT TIMES. ACROSS THE NORTHERN  
STATES, ADVANCING SHORTWAVE ENERGY AND SURFACE LOW  
PRESSURE/LEADING WARM FRONT SHOULD ENCOURAGE CONVECTIVE  
DEVELOPMENT WITHIN AN AREA FROM THE NORTHERN PLAINS INTO WESTERN  
GREAT LAKES FROM LATE WEEK INTO THE WEEKEND. SOME THUNDERSTORMS  
MAY PRODUCE HEAVY RAINFALL.  
 
ACROSS THE WEST, FLATTER FLOW ALOFT OVER NORTHERN AREAS WILL BRING  
TEMPERATURES DOWN TO NEAR OR SLIGHTLY BELOW NORMAL. EXPECT THE  
GREAT BASIN/SOUTHWEST TO SEE ABOVE NORMAL MIN TEMPS THROUGH THE  
PERIOD BUT HIGHS WILL LIKELY BE MORE MODERATE. A WAVY FRONT  
PUSHING INTO THE NORTHERN U.S. WILL BRING AN AREA OF WELL BELOW  
NORMAL READINGS INTO THE NORTHERN PLAINS/UPPER MS VALLEY WED-THU.  
THEN FLATTENING OF THE UPPER PATTERN WILL ENCOURAGE A WARMING  
TREND TO ABOVE NORMAL LEVELS, PROGRESSING FROM THE NORTHERN PLAINS  
INTO GREAT LAKES DURING FRI-SUN. CLOUDS/RAINFALL SHOULD KEEP THE  
SOUTHEAST BELOW NORMAL FOR HIGHS ON MOST DAYS. FLOW AROUND THE  
BERMUDA HIGH WILL PROMOTE ABOVE NORMAL LOWS OVER THE  
MID-ATLANTIC/NORTHEAST.  
 
RAUSCH  
 
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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