795  
FXUS02 KWBC 011559  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1159 AM EDT WED AUG 01 2018  
 
VALID 12Z SAT AUG 04 2018 - 12Z WED AUG 08 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
THE OVERALL OVERALL HAS NOT CHANGED WITH THE EASTERN PACIFIC  
TROUGH SITTING OFFSHORE OF THE PACIFIC NORTHWEST. IN ADDITION, A  
TROUGH WILL DEVELOP OVER THE NORTHERN PLAINS AND MOVE EASTWARD  
OVER THE GREAT LAKES/OHIO VALLEY AND A STRONG UPPER RIDGE  
DOMINATING THE WESTERN U.S.  
 
MODELS HAVE BEGUN TO CONVERGE ON A SOLUTION DEALING WITH THE UPPER  
LOW/TROUGH OVER THE EASTERN PACIFIC IN THE FIRST PART OF THE  
MEDIUM RANGE. THE 00Z ECMWF HAS BEGAN TO TREND TOWARD THE 00Z/06Z  
GFS AND 00Z CMC WITH REGARDS TO THE ORIENTATION OF THE CLOSED  
UPPER LOW THROUGH THE MEDIUM RANGE--BEING MUCH FARTHER SOUTH AND  
WEST THAN IN PREVIOUS RUNS. IN FACT, THE GFS, ECMWF, CMC AND  
UKMET HAVE ALL SHOWN THE TREND TOWARD A CLOSED UPPER LOW REMAINING  
WELL OFF THE WEST COAST THROUGH DAY 7. HOWEVER, THE ENSEMBLE MEANS  
ARE CONSISTENTLY SHOWING A TROUGH OFF THE WEST COAST AND CLOSER TO  
THE COAST--WITH THE 00Z ECENS HINTING AT TRENDING TOWARD A CLOSED  
LOW. WPC USED A BLEND OF THE PREVIOUSLY MENTIONED 00Z RUNS OF THE  
GFS/ECMWF/CMC/UKMET IN THE BEGINNING OF THE MEDIUM RANGE PERIOD AS  
THE AGREEMENT OVERALL WAS GOOD. BY THE END OF THE PERIOD, USED  
MORE OF THE 00Z ECENS AND 00Z NAEFS TO INCORPORATE BOTH THE CMC  
MEAN AND GEFS TO TAKE INTO ACCOUNT THE UNCERTAINTY WITH THE  
HANDLING OF THE UPPER LOW/TROUGH.  
 
THE FORECAST IN THE EASTERN U.S. CONTINUES TO BE LESS SENSITIVE.  
THE WEAKENING TROUGH OVER THE MISSISSIPPI VALLEY WILL WEAKEN EARLY  
ON IN THE PERIOD AS THE BERMUDA HIGH BUILDS ACROSS THE SOUTHEAST.  
THE UPPER RIDGE WILL SHIFT AND REMAIN OVER THE SOUTHWEST--HELPING  
TO KEEP THE EASTERN PACIFIC CLOSED LOW/UPPER TROUGH FROM MOVING  
ONSHORE. THERE WILL ALSO BE A TRANSITION OF SOUTHWESTERLY FLOW  
ACROSS SOUTH-CENTRAL CANADA/NORTHERN PLAINS TO AN EASTERN NORTH  
AMERICA MEAN TROUGH THAT ENDS UP SUPPRESSING ATLANTIC RIDGING THAT  
BUILDS INTO THE SOUTHEAST. THE UNCERTAINTY FOR THIS REGION OF THE  
FORECAST REMAINS WITH THE SHORTWAVE IMPULSES THAT IMPACT SURFACE  
FRONTS/WAVES. THE SELECTED BLEND MADE FOR THE UPSTREAM FORECAST  
PROVIDED A REASONABLE STARTING POINT FOR DEPICTING THE MOST COMMON  
ELEMENTS OF THE PATTERN EVOLUTION OVER CENTRAL/EASTERN PARTS OF  
THE COUNTRY.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
BECAUSE OF THE POSITION OF THE UPPER LOW/TROUGH IN THE EASTERN  
PACIFIC THE GUIDANCE HAS BEGAN TO HINT AT, THIS WILL HINT AT A DRY  
TREND FOR THE PACIFIC NORTHWEST AS A LOT LESS MOISTURE WILL BE  
BROUGHT INTO THE REGION. FOR NOW, MUCH LIGHTER RAINFALL FOR THIS  
AREA--WITH THE POSSIBILITY OF BEING COMPLETELY DRY. THE ENSEMBLE  
MEANS STILL SUPPORT LIGHT AMOUNTS OF RAIN IN THE AREA GIVEN THE  
POSITIONS OF THE TROUGH. DUE TO THIS UNCERTAINTY, THE FORECAST FOR  
TEMPERATURES WILL ALSO BE UNCERTAIN--WITH THE POSSIBILITY OF  
COOLER TEMPERATURES WITH A MORE ACTIVE WEATHER PATTERN OR WARMER  
DAYTIME TEMPERATURES IF THE DRY TREND SHOULD PERSEVERE.  
 
ELSEWHERE, EXPECT DIURNALLY DRIVEN SHOWERS/THUNDERSTORMS ALONG THE  
TERRAIN IN THE SOUTHWEST/FOUR CORNERS REGION THROUGH MOST OF THE  
PERIOD. FROM THE WEEKEND INTO EARLY NEXT WEEK A MEAN FRONTAL  
BOUNDARY WITH EMBEDDED WAVES WILL BE A FOCUS FOR PERIODS OF  
LOCALLY HEAVY/STRONG CONVECTION FROM THE NORTHERN PLAINS INTO THE  
GREAT LAKES. TOWARD MIDWEEK THE GRADUAL DEVELOPMENT OF UPPER  
TROUGHING OVER THE EAST SHOULD BRING ORGANIZED ACTIVITY INTO THE  
APPALACHIANS AND MID-ATLANTIC. BEFORE THAT OCCURS, THE BERMUDA  
HIGH THAT WILL BUILD OVER THE SOUTHEAST WILL PROMOTE A DRIER TREND  
OVER THE EAST AFTER A WET SHORT RANGE PERIOD. HOWEVER, DIURNALLY  
DRIVEN SCATTERED THUNDERSTORMS CAN STILL BE EXPECTED. AREAS ALONG  
THE GULF COAST MAY SEE ONE OR MORE DAYS OF RAINFALL AS WELL. ABOVE  
NORMAL TEMPERATURES WILL BE FAIRLY WIDESPREAD EAST OF THE ROCKIES.  
WARMEST READINGS VERSUS NORMAL SHOULD EXIST FOR MORNING LOWS FROM  
THE UPPER MS VALLEY INTO NEW ENGLAND, WITH SOME POCKETS OF VERY  
WARM HIGHS FROM PORTIONS OF THE PLAINS INTO NORTHEAST ON ONE OR  
MORE DAYS.  
 
REINHART/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  
 

 
 
CLICK HERE TO GO TO PREVIOUS BULLETINS.

The Nexlab HPC Page Main Text Page