556  
FXUS02 KWBC 101540  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1039 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, PERHAPS SLOWED BY A WAVE ALONG THE FRONT.  
 
   
..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--GFS/FV3 GFS AND ECMWF--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 (ESPECIALLY THE ECMWF ENSEMBLE  
MEAN).  
 
FOR THE SHORTWAVE ENERGY REACHING THE NORTHWEST AROUND DAY 4 WED,  
THE STRENGTH OF THE INITIAL WESTERN RIDGE SHOULD SUPPORT LEANING  
AWAY FROM THE STRONGER SOLUTIONS LIKE THE 00Z UKMET AT LEAST NEAR  
THE WEST COAST. AGAIN, A GFS/ECMWF BLEND SUFFICED.  
 
BY THE LATTER HALF OF THE PERIOD THERE REMAIN RATHER NOTICEABLY  
EAST-WEST TIMING DIFFERENCES WITH THE SYSTEM TRACKING ACROSS THE  
UPPER GREAT LAKES. TRENDS SEEM TO FAVOR A BIT QUICKER PROGRESSION  
BUT ONLY NUDGED THE FORECAST FORWARD A BIT BASED ON THE LATEST  
ENSEMBLES GIVEN THE UNCERTAINTY. THIS BASICALLY LIED BETWEEN THE  
00Z GFS/ECMWF.  
 
OVER FLORIDA AND THE TROPICS, MODELS/ENSEMBLES HAVE BEEN SHOWING  
SOME SIGNS OF A SURGE OUT OF THE WESTERN CARIBBEAN AND/OR FROM THE  
WESTERN ATLANTIC VIA A WEAK TROPICAL WAVE (SEE THE LATEST NHC  
OUTLOOKS FOR MORE INFORMATION). THIS WOULD EITHER RIDE UP ALONG  
THE FRONT (ECMWF WAS A RATHER AGGRESSIVE EXAMPLE) OR MERGE INTO  
THE FRONT FROM THE EAST (LIKE SOME GFS RUNS). FOR NOW KEPT A  
STATIONARY FRONT NEAR THE FLORIDA STRAITS WITH AN INCREASED CHANCE  
OF RAIN TO ITS NORTH.  
 
   
..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.  
 
FRACASSO/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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