412  
FXUS02 KWBC 271628  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1227 PM EDT FRI JUL 27 2018  
 
VALID 12Z MON JUL 30 2018 - 12Z FRI AUG 03 2018  
   
..HOT TEMPERATURES OVER THE WEST GRADUALLY MODERATING
 
 
...HEAVY RAINFALL THREAT EXTENDING FROM THE CENTRAL PLAINS/MS  
VALLEY TO SOUTHEAST/EASTERN U.S...  
   
..PATTERN OVERVIEW AND WEATHER HIGHLIGHTS/THREATS
 
 
MUCH OF THE CENTRAL AND EASTERN U.S. WILL HAVE A MULTI-DAY THREAT  
OF CONVECTION/HEAVY RAINFALL; LEADING TO AN ELEVATED RISK FOR  
FLOODING, ESPECIALLY FOR THE SOUTH APPALACHIAN REGION. ENERGY  
DROPPING THROUGH THE PLAINS AS OF EARLY NEXT WEEK WILL CARVE OUT  
ANOTHER EASTERN U.S. UPPER TROUGH THAT SHOULD ACHIEVE ITS GREATEST  
DEPTH AROUND MIDWEEK BEFORE TRENDING WEAKER. A STEADY INFLUX OF  
GULF MOISTURE FEEDING INTO THIS SYSTEM WILL INCREASE PRECIPITATION  
EFFICIENCY. AREAL AVERAGES OVER THE COURSE OF 7 DAYS ARE FORECAST  
TO BE 2 TO 4 INCHES, WITH ISOLATED AMOUNTS EXCEEDING 5 INCHES FOR  
THE SOUTHEAST AND MID-ATLANTIC REGIONS. SOME AREAS OF  
MODERATE-HEAVY RAINFALL MAY EXTEND INTO PARTS OF THE GREAT  
LAKES/APPALACHIANS/MID-ATLANTIC. THE PATTERN WILL PROMOTE BELOW  
NORMAL TEMPERATURES FROM THE PLAINS INTO THE SOUTHEAST WITH  
GREATEST NEGATIVE ANOMALIES OF MINUS 5-15F MOST LIKELY OVER PARTS  
OF THE PLAINS EARLY IN THE WEEK.  
 
MUCH OF THE SOUTHWEST WILL CONTINUE TO BE HOT ALTHOUGH  
TEMPERATURES WILL BE MODERATING THROUGH THE EXTENDED PERIODS. THE  
RIDGE OVER THE WEST WILL BECOME SLIGHTLY FLATTEN AS A TROUGH/LOW  
PRESSURE PERSISTS NEAR THE THE PACIFIC NORTHWEST COAST. BY LATE  
WEEK THIS ENERGY SHOULD SUPPORT NORTHERN PLAINS LOW PRESSURE WITH  
A CORRESPONDING INCREASE IN CONVECTION. HIGHEST ANOMALIES OVERALL  
SHOULD BE OVER THE NORTHWEST ON MON-TUE. THE GREAT  
BASIN/SOUTHWEST WILL LIKELY REMAIN QUITE WARM FOR MINS THROUGH THE  
END OF THE WEEK WITH HIGHS TENDING TO BE MORE MODESTLY ABOVE  
NORMAL (THOUGH STILL HOT ON AN ABSOLUTE BASIS). THE NORTHWEST  
SHOULD TREND BELOW NORMAL FOR HIGHS BY THE LATTER HALF OF THE  
WEEK.  
 
   
..GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
THE LATEST GUIDANCE CONTINUES WITH THE SYNOPTIC PATTERN OF A RIDGE  
OVER THE WEST, A DIGGING TROUGH OVER THE CENTRAL U.S. AND A  
RETROGRADING RIDGE OVER THE ATLANTIC/EAST COAST. DIFFERENCES ON  
THE TIMING AND PLACEMENT OF STORM SPECIFIC DETAILS FOR THE  
EAST-CENTRAL U.S. TROUGH IN PART DUE TO HOW FAR WEST THE RIDGE  
REACHES THE EAST COAST. THE DETERMINISTIC/ENSEMBLE MODELS HAVE  
CONTINUED ISSUES IN RESOLVING THE AREA OF LOW PRESSURE OFFSHORE OF  
THE PACIFIC NORTHWEST COAST, THEREFORE CONFIDENCE REMAINS LOW OVER  
THIS REGION. POSSIBILITIES RANGE FROM A FAIRLY COHESIVE  
LOW/SHORTWAVE WHOSE TIMING VARIES BY SOLUTION TO SOME ENERGY  
EJECTING AHEAD WHILE LINGERING ENERGY REMAINS NEAR THE PACIFIC  
NORTHWEST. AT LEAST THE MODELS/MEANS SHARE THE COMMON IDEA OF A  
GENERAL AREAS OF SURFACE LOW PRESSURE OVER/NEAR THE NORTHERN  
PLAINS LATE IN THE PERIOD.  
 
THE INITIAL FORECAST STARTED WITH 00 UTC ECWMF/CMC/UKMET AND 06  
UTC GFS COMPROMISE THROUGH TUESDAY JULY 31ST. FROM WEDNESDAY  
AUGUST 1ST THE 00 UTC NAEFS/GEFS/ECENS WAS INTRODUCED INTO THE  
BLEND AND INCREASED IN WEIGHTING GRADUALLY THROUGH THE END OF THE  
EXTENDED PERIOD ON FRIDAY AUGUST 3RD.  
 
CAMPBELL/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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