999  
FXUS02 KWBC 100657  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
156 AM EST SAT NOV 10 2018  
 
VALID 12Z TUE NOV 13 2018 - 12Z SAT NOV 17 2018  
   
..OVERVIEW
 
 
MOST GUIDANCE MAINTAINS GOOD CONTINUITY IN PRINCIPLE. THE  
MAJORITY CLUSTER SHOWS A BRIEF FLATTENING OF THE INITIALLY  
SHARP/AMPLIFIED UPPER LEVEL WESTERN RIDGE-EASTERN TROUGH PATTERN  
BEFORE A SOMEWHAT BROADER/LESS AMPLIFIED RIDGE-TROUGH EMERGE LATE  
IN THE PERIOD AFTER INCOMING PACIFIC ENERGY PASSES THROUGH THE  
WESTERN STATES. WITHIN THIS EVOLUTION THE FIRST SYSTEM OF  
INTEREST WILL BE A RAPIDLY STRENGTHENING STORM TRACKING FROM THE  
MID-ATLANTIC INTO EXTREME EASTERN CANADA TUE-WED. THE PROGRESSIVE  
PACIFIC ENERGY WILL LIKELY BRING A WEAK FRONT INTO THE NORTHWEST  
AROUND WED AND THEN SUPPORT AN AREA OF LOW PRESSURE REACHING NEAR  
THE UPPER GREAT LAKES LATE IN THE WEEK. UPSTREAM PACIFIC  
TROUGHING ALOFT LATE IN THE PERIOD SHOULD PUSH A FRONT TOWARD THE  
NORTHWEST BY FRI-SAT.  
 
   
..GUIDANCE/UNCERTAINTY ASSESSMENT
 
 
FOR THE DEVELOPING EAST COAST INTO CANADA STORM EARLY IN THE  
PERIOD, IMPORTANT SUBTLE DETAIL DIFFERENCES REMAIN BUT THESE ARE  
GENERALLY WITHIN TYPICAL GUIDANCE ERROR FOR FORECASTS 3-4 DAYS OUT  
IN TIME. STARTING WITH A CONSENSUS OPERATIONAL MODEL BLEND--MORE  
12Z GFS/FV3 GFS AND 12Z ECMWF THAN 12Z UKMET/CMC--YIELDED A  
SOLUTION VERY CLOSE TO CONTINUITY FROM THE PAST COUPLE CYCLES.  
 
BEHIND THIS SYSTEM THERE IS STILL A FAIR AMOUNT OF  
UNCERTAINTY/RELATIVELY LOW CONFIDENCE IN THE SPECIFICS OF RESIDUAL  
TRAILING SHORTWAVE ENERGY THAT MAY DRIFT EASTWARD FROM THE  
SOUTHERN PLAINS/NORTHERN MEXICO AFTER SEPARATING FROM THE REST OF  
THE OVERALL TROUGH THAT QUICKLY CROSSES THE EASTERN U.S. TAKEN AS  
A WHOLE THE LATEST MODELS/MEANS SEEM TO BE SIGNALING INCREASED  
POTENTIAL FOR SOME TRAILING SHORTWAVE ENERGY TO CROSS THE SOUTHERN  
LATITUDES BUT IN WEAK ENOUGH FORM TO KEEP PRECIPITATION COVERAGE  
AND TOTALS ON THE MODEST SIDE, WHILE OPERATIONAL RUNS SUGGEST MUCH  
LESS COVERAGE OF LIGHT ACTIVITY OVER THE SOUTHEAST/MID-ATLANTIC  
THAN SEEN IN THE ENSEMBLE MEANS.  
 
FOR THE SHORTWAVE ENERGY REACHING THE NORTHWEST AROUND DAY 4 WED  
THE CMC CONTINUES TO BE THE MOST AMPLIFIED BUT THE 00Z UKMET HAS  
COME IN WITH A RATHER STRONG SOLUTION AS WELL. THIS RELATIVE  
STRENGTH VERSUS OTHER GUIDANCE PERSISTS DOWNSTREAM AS THE ENERGY  
FEEDS INTO THE MEAN TROUGH. STRENGTH OF THE INITIAL WESTERN RIDGE  
SHOULD SUPPORT LEANING AWAY FROM THE STRONGER SOLUTIONS AT LEAST  
NEAR THE WEST COAST.  
 
BY THE LATTER HALF OF THE PERIOD GFS RUNS THUS FAR HAVE BEEN MORE  
EAGER THAN MOST OTHER SOLUTIONS TO BRING ENERGY FROM THE NEXT  
EASTERN PACIFIC UPPER TROUGH INTO WESTERN NORTH AMERICA. THIS  
LIKELY PLAYS A PART IN THE 18Z/00Z GFS RUNS IN PARTICULAR BECOMING  
FAIRLY FAST WITH THE SYSTEM TRACKING ACROSS THE UPPER GREAT LAKES.  
THE 12Z GFS/FV3 GFS WERE CLOSER TO CONSENSUS (WHICH INCLUDED THE  
GEFS MEAN) FOR THE GREAT LAKES SYSTEM. EVEN WITH THIS CONSENSUS  
THERE IS ENOUGH GUIDANCE SPREAD AND ECMWF INCONSISTENCY TO TEMPER  
CONFIDENCE IN A SPECIFIC SCENARIO FOR THE TIME BEING. ALONG THE  
WEST COAST LEANING MORE TOWARD THE MEANS BY DAYS 6-7 HELPED KEEP  
THE FORECAST BETWEEN THE FAST GFS AND SLOWER ECMWF.  
 
FOR DAYS 3-4 TUE-WED, THE BLEND FAVORED FOR THE EAST COAST SYSTEM  
REPRESENTED CONSENSUS WELL ELSEWHERE WITH CMC WEIGHT SUFFICIENTLY  
LOW TO DOWNPLAY ITS STRONGER WEST COAST SHORTWAVE BY DAY 4. DAY 5  
EXCLUDED THE UKMET DUE TO IT BECOMING OUT OF PHASE OVER THE  
NORTHERN U.S./SOUTHERN CANADA WHILE STARTING TO INCORPORATE 18Z  
GEFS/12Z ECMWF ENSEMBLE MEANS. DAYS 6-7 STARTED WITH 60-70  
PERCENT ENSEMBLE MEANS WITH THE 12Z FV3 GFS/ECMWF PROVIDING THE  
REST OF THE INPUT.  
 
   
..WEATHER HIGHLIGHTS/THREATS
 
 
THE STRENGTHENING EAST COAST STORM LIKELY TO REACH CANADA BY WED  
WILL BRING SIGNIFICANT PRECIPITATION TO PORTIONS OF THE NORTHEAST  
WITH HIGHEST TOTALS MOST LIKELY NEAR THE NEW ENGLAND COAST.  
EXPECT RAIN ALONG AND SOMEWHAT INLAND FROM THE COAST WITH ANY SNOW  
TENDING TO BE CONFINED TO WESTERN NEW ENGLAND, THE GREAT LAKES,  
AND APPALACHIANS. SOMEWHAT LESSER TOTALS ARE LIKELY ALONG THE  
COLD FRONT CROSSING THE SOUTHEAST. LAKE EFFECT ACTIVITY SHOULD  
PERSIST AT LEAST INTO MIDWEEK. PARTS OF THE NORTHEAST MAY SEE A  
PERIOD OF BREEZY TO WINDY CONDITIONS AFTER PASSAGE OF THE SURFACE  
LOW. AFTER THE EAST COAST SYSTEM DEPARTS, THE CONTIGUOUS U.S.  
SHOULD SEE FAIRLY LOW COVERAGE OF MEANINGFUL PRECIPITATION. THE  
PACIFIC NORTHWEST WILL LIKELY SEE TWO EPISODES OF RAIN/HIGHER  
ELEVATION SNOW, THE FIRST AROUND MIDWEEK AND A SECOND ONE TOWARD  
FRI AND/OR SAT. THE LATTER EVENT SHOULD HAVE SOMEWHAT HIGHER  
AMOUNTS THAN THE FIRST. LOW LEVEL FLOW FROM THE ATLANTIC MAY  
BRING SOME SHOWERS TO THE FLORIDA PENINSULA WHILE LOW CONFIDENCE  
SHORTWAVE ENERGY THAT COULD CROSS PARTS OF THE SOUTH MAY GENERATE  
LIGHT RAINFALL OVER PARTS OF THE SOUTHEAST. PRECIPITATION TOTALS  
SHOULD BE FAIRLY MODEST WITH THE SYSTEM FORECAST TO CROSS THE  
UPPER GREAT LAKES AROUND THU-FRI.  
 
MUCH BELOW NORMAL TEMPERATURES ARE LIKELY TUE-WED FROM THE  
SOUTHERN/EASTERN PLAINS INTO MOST OF THE EAST, WITH DECENT  
COVERAGE OF HIGHS 20F OR MORE BELOW NORMAL AND ONLY SLIGHTLY LESS  
EXTREME ANOMALIES FOR MORNING LOWS. A FEW DAILY RECORDS MAY BE  
POSSIBLE WITHIN THIS AREA. MUCH OF THE EASTERN HALF OF THE LOWER  
48 WILL LIKELY REMAIN BELOW NORMAL FOR THE REST OF THE PERIOD BUT  
WITH SOME MODERATION COMPARED TO TUE-WED. ON THE OTHER HAND ABOVE  
NORMAL READINGS WILL PREVAIL FROM MOST OF THE WEST INTO THE  
NORTHERN HIGH PLAINS. THERE MAY BE LOCALIZED PLUS 10-15F  
ANOMALIES FOR MIN/MAX TEMPERATURES FROM WED ONWARD.  
 
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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