193  
FXUS02 KWBC 311600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT FRI AUG 31 2018  
 
VALID 12Z MON SEP 03 2018 - 12Z FRI SEP 07 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
THE MAIN FIXTURE IN THE SYNOPTIC-SCALE PATTERN WILL BE AN  
EXPANSIVE MID/UPPER-LEVEL RIDGE EXTENDING FROM THE MISSISSIPPI  
RIVER EASTWARD TO THE WESTERN ATLANTIC. EXPECTED TO BE AROUND 2 TO  
2.5 SIGMA ABOVE CLIMATOLOGY, ITS PRESENCE SHOULD DOMINATE THE  
PATTERN WITH SOME WEAKENING BY DAY 7/SEPTEMBER 7 AS A BACKDOOR  
FRONT DROPS SOUTHWARD ACROSS NEW ENGLAND. GENERALLY SPEAKING,  
WOULD SAY THE MODELS ARE IN DECENT AGREEMENT WITH ITS POSITION AND  
STRENGTH. TO THE SOUTH OF THE POSITIVE HEIGHT ANOMALY, SOME SORT  
OF TROPICAL DISTURBANCE IS PRIMED TO SLIDE WESTWARD ACROSS THE  
FLORIDA PENINSULA INTO THE GULF OF MEXICO. WHILE IT MAY FEATURE A  
RATHER WEAK AREA OF SURFACE LOW PRESSURE, THE ECMWF HAS BEEN  
TRENDING DOWNWARD WITH ITS STRENGTH IN RECENT CYCLES. ENSEMBLE LOW  
PLOTS STILL SUGGEST ITS PRESENCE WITH THE GEFS MEMBERS FINALLY  
SHOWING UP IN THE 00Z CYCLE. THE NATIONAL HURRICANE CENTER  
INDICATES A 10 PERCENT CHANCE FOR TROPICAL CYCLONE GENESIS TO  
OCCUR DURING THE NEXT 5 DAYS WITH STRONG VERTICAL SHEAR BEING A  
MAIN INHIBITING FACTOR.  
 
ACROSS THE WESTERN/CENTRAL PORTIONS OF THE CONTINENT, A CONVEYOR  
BELT OF SHORTWAVES SHOULD CONTINUE TO SKIRT THE INTERNATIONAL  
BORDER WITH CANADA WHILE AMPLIFYING DOWNSTREAM ACROSS  
SASKATCHEWAN/MANITOBA. IT APPEARS THE 06Z/00Z GFS AND 00Z  
GFS-PARALLEL HAVE JOINED RECENT RUNS OF THE ECMWF BEING MORE  
AMPLIFIED BY MID-WEEK. THE GUIDANCE HAS BEEN TRENDING TOWARD THE  
ALLOWANCE OF MORE DENTING IN THE UPPER RIDGE. WHILE THIS SHORTWAVE  
LIFTS INTO THE HIGHER LATITUDES OF CANADA, A DIGGING LONGWAVE  
TROUGH TAKES SHAPE OVER THE EASTERN PACIFIC DURING THE DAY 5-7,  
SEPTEMBER 5-7 PERIOD. ENSEMBLE SPAGHETTI PLOTS DEPICT BUILDING  
SPREAD WITH THIS SYSTEM ALTHOUGH RECENT GUIDANCE SUGGESTS A  
GREATER LEVEL OF AMPLIFICATION. THIS SEEMS TO BE LARGELY DRIVEN BY  
UPSTREAM INFLUENCES FROM THE EXTRATROPICAL TRANSITION OF SUPER  
TYPHOON JEBI. ONE NOTABLE DIFFERENCE IS THE OPERATIONAL SOLUTIONS,  
PRIMARILY THE GFS, ARE QUICKER THAN THE MORE CLUSTERED ENSEMBLE  
MEANS LATE IN THE FORECAST.  
 
WITH REASONABLE MODEL AGREEMENT THROUGH WEDNESDAY, GENERALLY  
LEANED ON A COMBINATION OF THE 00Z GFS/GFS-PARALLEL, ECMWF, AND  
CMC SOLUTIONS WITH A BIT OF ENSEMBLE MEANS INCORPORATED BY  
MID-WEEK. THEREAFTER, ATTEMPTED TO BUILD THE FORECAST AROUND THE  
00Z GEFS/00Z ECMWF ENSEMBLE MEANS TO ULTIMATELY HOLD THE UPPER  
TROUGH BACK A BIT ALONG THE WEST COAST.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
THE CORRIDOR OF WARMER TEMPERATURES RELATIVE TO EARLY SEPTEMBER  
CLIMATOLOGY WILL RESIDE FROM THE GREAT LAKES EASTWARD INTO THE  
NORTHEASTERN U.S. IN RESPONSE TO THE STRONG RIDGE ALOFT. HIGH  
TEMPERATURES SHOULD GENERALLY BE AROUND 5 TO 10 DEGREES ABOVE  
AVERAGE ALTHOUGH SLIGHTLY HIGHER NUMBERS CAN BE EXPECTED OVER THE  
UPPER MID-ATLANTIC/LOWER NEW ENGLAND. SIMILAR DEPARTURES ARE  
LIKELY DURING THE OVERNIGHT HOURS AS WELL WHICH MAY LEAD TO A SLEW  
OF DAILY RECORDS BEING BROKEN, ESPECIALLY ON TUESDAY AND WEDNESDAY  
MORNINGS. MEANWHILE, THE COOLER SPOT WILL LIKELY BE OVER THE UPPER  
INTERMOUNTAIN WEST AND NORTHERN ROCKIES, PARTICULARLY ON TUESDAY  
WITH HIGHS ONLY IN THE 60S.  
 
REGARDING PRECIPITATION, MULTIPLE ROUNDS OF CONVECTION ARE IN THE  
FORECAST ALONG THE SLOW MOVING FRONTAL ZONE STRETCHING FROM THE  
CENTRAL U.S. INTO THE GREAT LAKES REGION. WHILE 24-HOUR AMOUNTS DO  
NOT APPEAR TO BE EXCESSIVE IN NATURE, THE MULTI-DAY NATURE OF  
THESE EVENTS COULD PRODUCE HYDROLOGIC ISSUES AT SOME POINT DURING  
THE PERIOD. OTHERWISE, EXPECT WIDESPREAD WARM SECTOR CONVECTION  
SOUTH OF THE BOUNDARY WITH A BETTER FOCUS ALONG THE GULF COAST.  
THIS IS IN RESPONSE TO BETTER MOISTURE QUALITY AS WELL AS THE  
MENTIONED TROPICAL WAVE TRACKING WESTWARD ACROSS THE GULF OF  
MEXICO. FARTHER WEST, SOME CONVECTIVE CHANCES WILL RETURN TO THE  
FOUR CORNERS REGION ALTHOUGH MOST SOLUTIONS FAVOR HIGHER AMOUNTS  
EASTWARD INTO THE ADJACENT HIGH PLAINS.  
 
RUBIN-OSTER  
 
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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