311  
FXUS02 KWBC 021349  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
948 AM EDT THU AUG 02 2018  
 
VALID 12Z SUN AUG 05 2018 - 12Z THU AUG 09 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
THE GUIDANCE SHOWS VERY GOOD AGREEMENT ON TIMING OF SYSTEMS IN AND  
NEAR NORTH AMERICA, WITH SOME DEPTH ISSUES NOTED. OVERALL, THE  
GUIDANCE HAS MAINTAINED BETTER DAY TO DAY CONSISTENCY THAN SEEN  
THIS TIME YESTERDAY. WHILE THE 00Z CANADIAN IS STRONGER THAN  
OTHER GUIDANCE WITH TROUGHING DEVELOPING NEAR THE GREAT LAKES, IT  
WAS THE FIRST TO START THE TREND TOWARDS WHAT THE GUIDANCE NOW  
ADVERTISES.  
 
THE 500 HPA HEIGHTS, SURFACE PRESSURES, FRONTS, AND WINDS ARE  
BASED ON A BLEND OF THE 00Z CANADIAN, 00Z UKMET, 00Z ECMWF, AND  
06Z GFS THROUGH TUESDAY MORNING TO DEAL WITH THE SMALL DIFFERENCES  
SEEN IN THE GUIDANCE. THEREAFTER, INCORPORATED INCREASING AMOUNTS  
OF THE 00Z ECMWF AND 00Z NAEFS MEANS WHICH RAMP UP TO 40% OF THE  
BLEND BY NEXT THURSDAY. THE WEATHER, DEW POINT, CLOUD,  
TEMPERATURE, AND RAIN CHANCE GRIDS WILL REFLECT A MORE EVEN BLEND  
OF THE DETERMINISTIC AND ENSEMBLE GUIDANCE. THE DAYS 4-7 QPF IS  
LIKELY TO REFLECT A ROUGH BLEND OF THE 06Z GFS, 00Z CANADIAN, 00Z  
ECMWF, AND 12Z NATIONAL BLEND OF MODELS. SHOULD THE 12Z GFS HAVE  
REASONABLE MASS FIELDS, IT COULD BE INCLUDED AS WELL.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
WITH THE LATEST CYCLE OF GUIDANCE EITHER CONSISTENT WITH OR  
FURTHERING TRENDS TOWARD KEEPING THE EASTERN PACIFIC UPPER LOW  
WELL OFFSHORE THROUGH THE PERIOD WHILE UPPER RIDGING BUILDS OVER  
THE WEST, CONFIDENCE IS INCREASING THAT MOST OF THE WESTERN U.S.  
SHOULD SEE A WARMING TREND TO ABOVE NORMAL TEMPERATURES BY TUESDAY  
INTO NEXT THURSDAY. DRY CONDITIONS WILL LIKELY PREVAIL OVER MOST  
AREAS AS WELL, ASIDE FROM DIURNALLY FAVORED CONVECTION AT TIMES  
OVER PARTS OF THE FOUR CORNERS STATES. BEFORE THIS WARM-UP  
LOCATIONS FROM THE CENTRAL WEST COAST INTO THE NORTHERN ROCKIES  
MAY SEE BELOW NORMAL HIGHS ESPECIALLY ON SUNDAY. RECORD HIGH  
MINIMA ARE FORECAST ACROSS THE DESERT SOUTHWEST AND SOUTHERN  
CALIFORNIA.  
 
FARTHER EASTWARD THE GRADUAL DEVELOPMENT OF UPPER TROUGHING WILL  
HELP TO PUSH AN INITIAL WAVY FRONT OVER THE NORTHERN PLAINS  
SOUTHEASTWARD WITH TIME. AS A RESULT THE FOCUS FOR AREAS OF  
POTENTIALLY HEAVY/STRONG CONVECTION WILL SHIFT FROM THE UPPER MS  
VALLEY/GREAT LAKES/NORTH-CENTRAL PLAINS TOWARD/INTO THE  
EASTERN-SOUTHERN STATES. SOME RAINFALL IS ALSO POSSIBLE WITH  
ANOTHER FRONT THAT MAY DROP INTO THE NORTHERN STATES LATE IN THE  
PERIOD BUT LESS AVAILABLE MOISTURE SHOULD LEAD TO LOWER TOTALS  
THAN WITH THE ACTIVITY EARLIER IN THE PERIOD. AHEAD OF THESE  
FRONTS EARLY IN THE WEEK, A TYPICAL SUMMER-LIKE AIRMASS ACROSS  
PORTIONS OF THE SOUTH AND EAST MAY SEE SCATTERED AND GENERALLY  
LIGHT-MODERATE SHOWERS/THUNDERSTORMS. FOR TEMPERATURES EAST OF  
THE ROCKIES EXPECT AREAS FROM THE GREAT LAKES INTO THE NORTHEAST  
TO SEE THE WARMEST READINGS VERSUS NORMAL (ESPECIALLY FOR MORNING  
LOWS) IN THE SUNDAY-TUESDAY TIME FRAME. THE EXPECTED PATTERN  
EVOLUTION SHOULD YIELD NEAR TO SLIGHTLY BELOW NORMAL HIGHS OVER A  
MAJORITY OF THE EAST BY NEXT WEDNESDAY-THURSDAY. DUE TO THE  
AVAILABLE MOISTURE AND SLOWLY DECLINING TEMPERATURES/AVERAGES  
NORMALLY SEEN IN AUGUST, RECORD HIGH MINIMA ARE EXPECTED ACROSS  
SOUTHERN NEW ENGLAND.  
 
ROTH/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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