617  
FXUS02 KWBC 301601  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT MON JUL 30 2018  
 
VALID 12Z THU AUG 02 2018 - 12Z MON AUG 06 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
MODEL GUIDANCE THIS MORNING CONTINUES TO ADVERTISE A SLOW-MOVING  
POSITIVELY-TILTED TROUGH TO WEAKEN GRADUALLY IN PLACE ALONG THE  
MISSISSIPPI VALLEY AS A VERY STRONG BERMUDA HIGH ATTEMPTS TO  
EXTEND WESTWARD INTO THE SOUTHEAST THROUGH THE MEDIUM RANGE  
PERIOD. MEANWHILE, A COOL AIRMASS MOVING ACROSS THE NORTHERN  
PLAINS INTO THE GREAT LAKES WILL QUICKLY BE MODIFIED BY THE NEXT  
SHORTWAVE TROUGH MOVING FROM WEST TO EAST JUST NORTH OF THE  
U.S.-CANADIAN BORDER. THIS WILL BE FOLLOWED BY THE APPROACH OF A  
MORE AMPLIFIED CLOSED LOW FORECAST TO DROP SOUTHEASTWARD FROM  
ALASKA TO A POSITION OFF THE PACIFIC NORTHWEST COAST BY NEXT  
MONDAY.  
 
MODEL SOLUTIONS ARE IN GOOD AGREEMENT WITH THE SYNOPTIC PATTERN  
EVOLUTION OVER THE U.S. WITH THE MISSISSIPPI VALLEY UPPER TROUGH  
SLOWLY ERODING WITH TIME AS THE BERMUDA HIGH EXTENDS ITS INFLUENCE  
WESTWARD TOWARD THE WARM HIGH ALOFT OVER THE SOUTHERN ROCKIES.  
THE MAIN UNCERTAINTY LIES MAINLY FROM THE NORTHERN TIER INTO  
CANADA WHERE MODELS CONTINUE TO SHOW RUN-TO-RUN VARIABILITY ON  
HANDLING THE EASTWARD-MOVING SHORTWAVE TROUGH JUST NORTH OF THE  
BORDER. BY THIS WEEKEND INTO MONDAY OF NEXT WEEK, THE GFS HAS  
BEEN INDICATING A MORE AMPLIFIED SOUTHWARD-PLUNGING CLOSED LOW  
ACROSS THE NORTHEAST PACIFIC COMPARED WITH THE ECMWF. THE  
CANADIAN MODEL SHOWS A DECENT DEEP LOW POSITIONED IN BETWEEN THE  
GFS AND THE ECMWF.  
 
THE MORNING WPC GRID FIELDS WERE DERIVED USING A 50-50 BLEND OF  
THE 06Z GFS WITH THE 00Z ECMWF, MIXING IN WITH MORE OF THEIR  
ENSEMBLE MEANS TOWARD DAY 7. THIS YIELDS GRID FIELDS THAT ARE  
CLOSE TO CONTINUITY WITH THE PREVIOUS WPC PACKAGE.  
 
KONG  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
WITHIN THE FAVORABLE AREA FOR LOCALLY HEAVY RAINFALL OVER THE  
SOUTHEAST/SOUTHERN HALF OF THE APPALACHIANS AND POSSIBLY EXTENDING  
INTO PARTS OF THE MID-ATLANTIC, THE BEST ORGANIZED ACTIVITY SHOULD  
BE LATE THIS WEEK WHEN FLOW BETWEEN THE MS VALLEY UPPER TROUGH AND  
BERMUDA HIGH WILL DIRECT THE MOST FOCUSED GULF/ATLANTIC MOISTURE  
INTO THE REGION. A WEAKENING COLD/STATIONARY FRONT WILL PROVIDE A  
LOW-LEVEL FOCUS FOR CONVECTION AS WELL. BY SAT-MON EXPECT  
SHOWERS/STORMS TO BECOME GRADUALLY LIGHTER AND MORE SCATTERED AS  
FLOW ALOFT BECOMES LESS DEFINED AND THE SURFACE RIDGE AXIS DRIFTS  
SOUTHWESTWARD. THE NORTHEASTERN PLAINS INTO THE GREAT LAKES WILL  
BE ANOTHER REGION WITH ENHANCED RAINFALL POTENTIAL DURING THE  
PERIOD. SOME OF THE RAIN WILL COME WITH A WAVY FRONT SETTLING  
INTO THE REGION LATE THIS WEEK. THEN EXPECT HEAVIER/STRONGER  
CONVECTION WITH THE SYSTEM EMERGING INTO THE NORTHERN PLAINS BY  
FRI WITH THE LEADING WARM FRONT PROVIDING AN ADDED FOCUS. THE  
COLD FRONT TRAILING FROM THIS SYSTEM MAY DECELERATE WITH TIME,  
ALLOWING FOR SOME PERSISTENCE/TRAINING LATER IN THE PERIOD.  
MEANWHILE DIURNALLY FAVORED CONVECTION OF VARYING INTENSITY WILL  
CONTINUE OVER PORTIONS OF THE FOUR CORNERS STATES. THE AMPLIFYING  
UPPER TROUGH NEARING THE WEST COAST LATER IN THE PERIOD MAY  
EVENTUALLY BRING SOME MOISTURE TO THE PACIFIC NORTHWEST.  
 
EXPECTED PATTERN EVOLUTION WILL LIKELY LEAD TO AN AREA OF ABOVE  
NORMAL MIN AND/OR MAX TEMPERATURES BECOMING ORIENTED FROM THE  
NORTH-CENTRAL/CENTRAL PLAINS THROUGH THE GREAT LAKES/NORTHEAST.  
ANOMALIES EXCEEDING 10F SHOULD BE SOMEWHAT MORE COMMON FOR MORNING  
LOWS. THE SOUTHEASTERN THIRD OF THE COUNTRY WILL SEE COOLEST  
DAYTIME HIGHS VERSUS NORMAL LATE THIS WEEK WHEN CLOUDS/RAINFALL  
SHOULD BE MOST PREVALENT, FOLLOWED BY A TREND TOWARD NORMAL  
VALUES. OVER THE WEST, MIN TEMPS WILL LIKELY REMAIN QUITE WARM  
OVER AND SOUTH OF THE GREAT BASIN THROUGH THE PERIOD WHILE  
SLIGHTLY BELOW NORMAL HIGHS SHOULD PREVAIL OVER THE NORTHWEST.  
 
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