072  
FXUS02 KWBC 291600  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1200 PM EDT WED AUG 29 2018  
 
VALID 12Z SAT SEP 01 2018 - 12Z WED SEP 05 2018  
   
..PATTERN OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
 
 
ENTERING THE MONTH OF SEPTEMBER, A CASCADE OF SHORTWAVES WILL  
CONTINUE TO PUSH FROM WESTERN NORTH AMERICA EASTWARD TOWARD THE  
NORTH-CENTRAL U.S. EACH OF THESE PERTURBATIONS IN THE FLOW ARE OF  
RATHER LOW PREDICTABILITY AS MODELS EXHIBIT POOR RUN-TO-RUN  
CONTINUITY. THERE ARE INDIVIDUAL MEMBERS WITHIN THE ENSEMBLE  
SYSTEMS WHICH FAVOR MORE AMPLIFIED SCENARIOS. ALL OF THESE  
SHORTWAVES SHOULD GENERALLY REMAIN CONFINED TO LOCATIONS NEAR THE  
INTERNATIONAL BORDER WITH CANADA UNLESS ONE OF THESE MORE  
AMPLIFIED ENSEMBLE MEMBERS WERE TO VERIFY. AMONG THE GLOBAL  
GUIDANCE, THE 00Z CMC SEEMS TO BE TOO QUICK WITH EASTWARD EJECTION  
OF THESE EMBEDDED IMPULSES. ELSEWHERE, SOME MODELS INTERMITTENTLY  
SHOW A MODESTLY DEFINED SHORTWAVE APPROACHING THE NORTHERN  
CALIFORNIA COAST SOMETIME BETWEEN DAY 4-6, SEPTEMBER 2-4. MOST  
NOTABLY, THIS APPEARS IN THE 00Z GFS/12Z ECMWF OUTPUT. NOT ENOUGH  
CONFIDENCE EXISTS TO FULLY SUPPORT SUCH A SCENARIO AT THIS TIME.  
 
ACROSS THE EASTERN U.S., AFTER A TEMPORARY REPRIEVE, A SPRAWLING  
594-DM RIDGE SHOULD RETURN TO THE REGION BY MONDAY INTO THE MIDDLE  
OF THE WEEK. THIS HAS SEEMINGLY BEEN THE NEW PREFERRED LOCATION  
FOR A POSITIVE HEIGHT ANOMALY TO SITUATE ITSELF. MODEL AGREEMENT  
IS SOLID WITH NO SIGNIFICANT DIFFERENCES EVIDENT. WITHIN THE  
SUBTROPICS, THERE REMAIN CONTINUED HINTS AT SOME TROPICAL  
DISTURBANCE MOVING WESTWARD ACROSS THE FLORIDA PENINSULA INTO THE  
GULF OF MEXICO. IT IS MOSTLY A ECMWF DRIVEN SOLUTION ALTHOUGH THE  
00Z CMC ENSEMBLES SHOW A SMALL NUMBER OF MEMBERS. ALONG THE  
SOUTHEASTERN U.S. COAST, THE 00Z CMC/NAEFS ENSEMBLES FAVOR AN  
INVERTED TROUGH EARLY NEXT WEEK. THEY DO SEEM TO BE ON THEIR OWN  
WHICH CASTS DOUBT ON THEIR FORECASTS.  
 
A MULTI-MODEL CONSENSUS SOLUTION WAS UTILIZED WITH A GENERAL  
COMBINATION OF THE 06Z/00Z GFS, 00Z ECMWF, AND THEIR RESPECTIVE  
ENSEMBLE MEANS. BY DAY 5/SEPTEMBER 3 ONWARD, THE FORECAST WAS  
HEAVILY DRIVEN BY THE 06Z GEFS/00Z ECMWF ENSEMBLE MEANS GIVEN  
BUILDING UNCERTAINTY, PARTICULARLY WITHIN THE ACTIVE FLOW ALONG  
THE NORTHERN TIER STATES.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
GIVEN THE RETURN OF UPPER RIDGING TO THE EASTERN STATES,  
TEMPERATURES WILL LIKELY REMAIN ABOVE CLIMATOLOGY, PARTICULARLY  
NEXT WEEK. THE MOST ANOMALOUS READINGS ARE EXPECTED OVER THE  
NORTHEASTERN U.S. WITH NUMBERS AROUND 5 TO 10 DEGREES ABOVE  
AVERAGE. MEANWHILE, COOLER CONDITIONS SHOULD PREVAIL BACK ACROSS  
THE UPPER INTERMOUNTAIN WEST/NORTHERN ROCKIES AND EVENTUALLY INTO  
THE ADJACENT GREAT PLAINS. THE PASSAGE OF THE LONGWAVE TROUGH  
SHOULD ENCOURAGE A PERIOD OF COLD ADVECTION ALLOWING FOR  
TEMPERATURES IN THE UPPER 60S TO LOW 70S ON DAY 6/7, SEPTEMBER  
4-5. REGARDING PRECIPITATION, HEAVY RAINFALL WILL BE POSSIBLE  
ALONG THE SLOW MOVING FRONT, PARTICULARLY ACROSS THE MIDDLE  
MISSISSIPPI VALLEY INTO THE UPPER GREAT LAKES. OVER THE  
SOUTHEASTERN U.S., DEPENDING ON WHAT EMERGES OUT OF THE TROPICS,  
INCREASING QPF AMOUNTS ARE EXPECTED NEXT WEEK WHILE A RETURN OF  
CONVECTION TO THE FOUR CORNERS IS ANTICIPATED WITH MONSOONAL  
MOISTURE BACK IN PLACE.  
 
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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