011  
FXUS02 KWNH 300641  
PREEPD  
 
PRELIMINARY EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
240 AM EDT TUE AUG 30 2016  
 
VALID 12Z FRI SEP 02 2016 - 12Z TUE SEP 06 2016  
   
..OVERVIEW
 
 
GUIDANCE CONFIDENTLY SHOWS THE MEAN PATTERN SETTLING INTO AN ERN  
PAC RIDGE/WRN U.S. TROUGH/ERN RIDGE CONFIGURATION BUT WITH SOME  
EMBEDDED UNCERTAINTIES. THERE ARE VARIED SOLNS FOR SHRTWV DETAILS  
WITHIN THE WRN TROUGH WHILE FARTHER EWD THERE IS A FAIR AMOUNT OF  
SPREAD FOR HOW ENERGY IN THE SRN PART OF THE DEPARTING LATE WEEK  
EAST COAST TROUGH MAY LINGER OVER THE AREA. AS FOR TROPICAL  
FEATURES THE NATIONAL HURRICANE CENTER IS ISSUING ADVISORIES ON  
T.D. EIGHT WHICH SHOULD BE OUT OF THE PICTURE BY FRI...AND T.D.  
NINE WHICH IS FCST TO EMERGE OVER THE WRN ATLC AFTER CROSSING NRN  
FLORIDA IN THE LATTER PART OF THE SHORT RANGE PERIOD.  
COMPLICATING THE EAST COAST FCST IS HOW THE LINGERING ERN TROUGH  
ENERGY MAY INTERACT WITH T.D. NINE.  
 
   
..GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
WITH VARIOUS DETAIL DIFFS ARISING FAIRLY EARLY IN THE PERIOD THE  
LATEST MANUAL FCST STARTS WITH SOMEWHAT MORE THAN USUAL GEFS/ECMWF  
ENSEMBLE MEAN WEIGHTING VS OPERATIONAL RUNS EARLY-MID PERIOD  
BEFORE GOING ENTIRELY TO THE MEANS BY DAYS 6-7 SUN-TUE.  
 
WITHIN THE WRN MEAN TROUGH... SOME RECENT GFS RUNS INCL THE NEW  
00Z VERSION ARE SOMEWHAT ON THE SRN SIDE OF THE SPREAD WITH THE  
TRACK OF UPR LOW ENERGY THAT PROCEEDS FROM THE PAC NW TOWARD  
HUDSON BAY AND SUPPORTS VIGOROUS CANADIAN LOW PRES WITH A TRAILING  
COLD FRONT THAT REACHES THE NRN PLAINS. AMONG OTHER SOLNS THERE  
ARE STILL SOME TIMING/DEPTH/AMPLITUDE DIFFS ALOFT THAT HAVE AN  
INFLUENCE ON FRONTAL TIMING. FOR THE AMPLIFIED TROUGH THAT  
CONTINUES INTO THE WEST SAT ONWARD THE 12Z/18Z GEFS MEAN AND 12Z  
ECMWF MEAN HAVE ARRIVED AT VERY SIMILAR SOLNS AFTER THE FORMER  
TRENDED SOMEWHAT FASTER AND THE LATTER SHARPER AND SLOWER COMPARED  
TO 24 HRS AGO. THE MOST PROMINENT UNCERTAINTY DURING DAYS 5-7  
SUN-TUE WILL BE THE EVOLUTION OF EMBEDDED SHRTWV ENERGY ACROSS THE  
NRN HALF OF THE WEST AND INTO THE NRN PLAINS... WHICH WILL  
DETERMINE WAVE DETAILS ALONG THE NRN PLAINS FRONT. OVERALL PREFER  
AN INTERMEDIATE SOLN SLIGHTLY CLOSER TO THE ECMWF/ECMWF MEAN  
DURING THE FIRST HALF OF THE PERIOD THEN TRENDING TO AN ENSEMBLE  
MEAN BLEND WHILE AWAITING IMPROVED AGREEMENT SFC/ALOFT ACROSS THE  
NRN TIER LATER IN THE PERIOD.  
 
FCST CONFIDENCE OVER THE EAST COAST/WRN ATLC IS LOWER THAN DESIRED  
GIVEN UNCERTAINTY OVER WHETHER/HOW T.D. NINE AND WEAK UPR ENERGY  
BEING LEFT BEHIND BY THE DEPARTING ERN TROUGH MAY INTERACT... AND  
EVENTUALLY THE UNCERTAIN DEGREE OF WWD PROGRESS/EXTENT OF A CNTRL  
ATLC RIDGE BUILDING TOWARD BERMUDA. THE COMBINATION OF FEATURES  
INVOLVED IS MAKING IT VERY DIFFICULT FOR MODELS AND ENSEMBLE  
MEMBERS TO COME TO ANY SEMBLANCE OF REASONABLE AGREEMENT FOR T.D.  
NINE ONCE IT REACHES BEYOND THE NERN GULF OF MEXICO.  
EXTRAPOLATION OF THE 0300 UTC NHC ADVISORY BEYOND 00Z SUN YIELDS  
FAIRLY GOOD CONTINUITY WITH A WELL OFFSHORE TRACK AS AGREED UPON  
IN YDAYS DAYTIME COORDINATION. NOTE THAT RECENT GFS RUNS AND THE  
18Z CYCLE OF THE GEFS MEAN ARE AMONG A PORTION OF THE WIDE  
GUIDANCE SPREAD THAT WOULD YIELD GREATER INFLUENCE ON CONDS NEAR  
THE EAST COAST. FAVORING A SOLN CLOSER TO CONTINUITY LED TO USE  
OF THE 12Z GEFS MEAN OVER THE 18Z RUN FOR THAT COMPONENT OF THE  
FCST BLEND.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THOSE NEAR THE EAST COAST... AND THE SOUTHEAST/SRN MID ATLC COAST  
IN PARTICULAR... SHOULD CONTINUE TO MONITOR FCSTS FOR T.D. NINE  
WHICH WILL LIKELY BE ACCOMPANIED BY HVY RAIN/STRONG WINDS. THE  
EXTENT TO WHICH THE REST OF THE EAST COAST SEES ANY EFFECTS FROM  
T.D. NINE IS VERY UNCERTAIN AT THIS TIME. FROM THE NORTHWEST INTO  
THE PLAINS... MAJORITY OF PAC NW RNFL SHOULD BE EARLY IN THE  
PERIOD IN ASSOC WITH THE DEEPEST CORE OF ENERGY ALOFT. THE NRN  
ROCKIES SHOULD SEE PERIODS OF PCPN. AS THE LEADING SFC FRONT  
REACHES THE PLAINS AND LIKELY DECELERATES THERE ARE CONTINUED  
SIGNALS FOR HVY RNFL POTENTIAL FROM THE NRN-CNTRL PLAINS INTO THE  
UPR MS VLY/UPR GRTLKS. SOME CONVECTION WITHIN THIS AREA MAY ALSO  
BE ON THE STRONG SIDE. ELSEWHERE EXPECT SOME LINGERING RNFL OVER  
FL AND VICINITY WHILE THERE MAY BE ONE OR MORE PERIODS OF  
SHWRS/TSTMS NEAR THE GULF COAST AND OVER THE SRN HALF OF THE  
ROCKIES.  
 
THE NRN PLAINS WILL SEE THE MOST DRAMATIC CHANGE IN TEMPS DURING  
THE FCST PERIOD AS ADVANCING COOL AIR OVER THE WEST DISPLACES LATE  
WEEK HEAT. NRN PLAINS HIGHS SHOULD BE 10-20F ABOVE NORMAL FRI BUT  
THEN FALL TO 5-15F BELOW NORMAL BY SUN-MON. HIGH PRESSURE  
BUILDING INTO THE EAST WILL BRING NEAR TO SLIGHTLY BELOW NORMAL  
TEMPS DURING THE FIRST HALF OF THE PERIOD BUT WARM FLOW ON THE WRN  
SIDE OF THE HIGH WILL LIKELY PUSH HIGHS 10-15F ABOVE NORMAL FROM  
THE OH VLY/GRTLKS INTO NORTHEAST BY EARLY NEXT WEEK.  
 
RAUSCH  
 

 
 
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