631  
FXUS02 KWBC 200700  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
259 AM EDT SAT OCT 20 2018  
 
VALID 12Z TUE OCT 23 2018 - 12Z SAT OCT 27 2018  
 
...GUIDANCE/PREDICTABILITY ASSESSMENT AND WEATHER  
HIGHLIGHTS/THREATS...  
 
A SPLIT FLOW REGIME WILL BE IN PLACE FAVORING A WEAK SOUTHERN  
STREAM TROUGH TRACKING FROM THE DESERT SOUTHWEST TOWARD THE MIDDLE  
OF THE COUNTRY. GRADUALLY SOME PHASING WITH THE NORTHERN BRANCH OF  
THE JET COULD LEAD TO CYCLOGENESIS ACROSS THE NORTHERN GULF OF  
MEXICO WITH THE WAVE CURLING UP ALONG THE SOUTHEASTERN U.S. COAST.  
ACROSS THE MORE NORTHERN LATITUDES, LOWER HEIGHTS SHOULD  
CONGREGATE OVER NORTHEASTERN NORTH AMERICA AS AN UPPER LOW  
CONTINUES TO SPIN OVER NORTHERN NUNAVUT. AMPLIFYING FLOW SWINGING  
THROUGH THE GREAT LAKES WILL ULTIMATELY AID IN THE DEVELOPMENT OF  
A COASTAL WAVE IN THE VICINITY OF NOVA SCOTIA BY LATE  
TUESDAY/EARLY WEDNESDAY. BACK TO THE NORTHEASTERN PACIFIC,  
MULTIPLE DEEP CYCLONES ARE LIKELY TO APPROACH WESTERN BRITISH  
COLUMBIA DURING THE DAY 3-5, OCTOBER 23-25 TIMEFRAME. WHILE MOST  
OF THE ACTION SHOULD STAY NORTH OF THE INTERNATIONAL BORDER WITH  
CANADA, THE MEAN FLOW SHOULD TURN MORE ZONAL ACROSS THE EASTERN  
PACIFIC ALLOWING MORE OF AN ONSHORE FLOW REGIME INTO THE PACIFIC  
NORTHWEST. TOWARD NEXT WEEKEND, BROAD RIDGING IS FORECAST TO  
GRADUALLY ENCOMPASS THE EASTERN PACIFIC WITH LONGWAVE TROUGHING  
EXPECTED TO COVER THE MIDDLE OF THE COUNTRY. GENERALLY SPEAKING,  
OUTSIDE OF THE MENTIONED AREAS OF CYCLOGENESIS, SYNOPTIC-SCALE  
GRADIENTS SHOULD REMAIN ON THE MORE WASHED OUT ACROSS THE  
REMAINDER OF THE NATION.  
 
EARLY ON, MODELS REMAIN AT ODDS WITH THE POSITION OF THE SURFACE  
LOW STRENGTHENING ON APPROACH INTO THE CANADIAN MARITIMES.  
ENSEMBLE PLOTS CLEARLY SHOW THE DICHOTOMY OF SOLUTIONS WITH THE  
12Z GEFS MEMBERS NORTH OF THE OTHER GLOBAL MODELS. OPERATIONAL  
FORECASTS SEEM TO STICK FAIRLY CLOSE TO THEIR RESPECTIVE CAMPS  
WITH THE 00Z GUIDANCE OFFERING VERY LITTLE CHANGE IN THESE  
SCENARIOS. WHILE A WAVE SHOULD SPIN UP, ITS PLACEMENT REMAINS  
UNCERTAIN. AS IT LIFTS TOWARD NEWFOUNDLAND, HIGH PRESSURE WILL  
BUILD OVER THE GREAT LAKES AND NORTHEASTERN U.S. THROUGH FRIDAY.  
BACK TO THE NORTHEASTERN PACIFIC, RATHER AMPED UP WAVES ARE  
ANTICIPATED ALTHOUGH MOST OF THE ACTION SHOULD STAY OVER COASTAL  
BRITISH COLUMBIA AND POINTS OFFSHORE. MODEL AGREEMENT EXISTS IN  
FLATTENING THE FLOW OUT TOWARD THE LATTER HALF OF THE PERIOD.  
UNCERTAINTY SEEMS TO MOSTLY CONCENTRATE WITH THE EVOLUTION OF THE  
PHASING ACROSS THE MIDDLE OF THE NATION LEADING TO MODEST  
CYCLOGENESIS IN THE GULF OF MEXICO. THE GEFS AND ECMWF ENSEMBLES  
REMAIN ALMOST A DAY APART WITH THE 27/1200Z LOW POSITION BEING  
NEAR THE NORTH CAROLINA COAST BY THE 12Z ECMWF WHILE THE 12Z GFS  
FAVORS A PLACEMENT NORTH OF TAMPA BAY, FLORIDA. THE 00Z ECMWF DID  
MAKE A SOUTHERN ADJUSTMENT PARTICULARLY IN LIGHT OF ITS PRIOR  
SOLUTION BEING ON THE FAR NORTHERN FRINGE OF ITS ENSEMBLES.  
OVERALL, A MULTI-MODEL CONSENSUS APPEARED REASONABLE THROUGH DAY  
4/WEDNESDAY BEFORE QUICKLY ADDING ENSEMBLE MEANS TO THE PICTURE.  
ATTEMPTED TO DOWNPLAY ANY INDIVIDUAL OPERATIONAL RUN BY THE DAY  
6/7, OCTOBER 26-27, WINDOW GIVEN ABUNDANT UNCERTAINTY WITH WAVE  
PLACEMENT AND INTENSITY.  
 
HEAVY RAINFALL IS LIKELY TO IMPACT THE GULF COAST REGION ALTHOUGH  
MANY SOLUTIONS DO KEEP THE MOST CONCENTRATED ACTIVITY OFFSHORE.  
THE CURRENT FORECAST FRONTAL BOUNDARIES KEEP THE SYSTEM OFFSHORE  
SUGGESTING ANY ACTIVITY INLAND WOULD BE MORE ELEVATED IN NATURE.  
EVENTUALLY THIS PRECIPITATION FOCUS WILL SHIFT NORTH AND EAST WITH  
THE POTENTIAL FOR WET CONDITIONS LATE IN THE WEEK OVER THE  
SOUTHEASTERN U.S. COAST. ACROSS THE PACIFIC NORTHWEST, THE  
PERSISTENCE OF ONSHORE FLOW WILL KEEP A STEADY FOCUS FOR UPSLOPE  
DRIVEN RAINFALL ACROSS THE OLYMPICS AND WASHINGTON CASCADES. IT  
APPEARS THE BETTER ACTIVITY WILL HOLD OFF UNTIL LATER IN THE WEEK  
AS THE MEAN FLOW TURNS MORE ZONAL IN NATURE. REGARDING WINTER  
THREATS, NORTHERN MAINE COULD SEE SOME SNOWFALL ACCUMULATIONS AS  
THE COASTAL LOW TAKES SHAPE NEAR NOVA SCOTIA BY TUESDAY/WEDNESDAY.  
LOOKING AT THE TEMPERATURE FORECAST, REGIONS EAST OF THE ROCKIES  
ARE FORECAST TO REMAIN BELOW CLIMATOLOGY GIVEN THE PERSISTENCE OF  
UPPER TROUGHING ACCOMPANIED BY ENHANCED PRECIPITATION CHANCES.  
DEPARTURES ON THE ORDER OF 10 TO 15 DEGREES ARE LIKELY OVER THE  
SOUTHERN PLAINS THROUGH THURSDAY SUGGESTING HIGHS STAY IN THE 50S  
AND 60S. MEANWHILE, SIMILAR ANOMALIES EXCEPT ON THE POSITIVE SIDE  
ARE NOTED FROM THE PACIFIC NORTHWEST EASTWARD INTO THE NORTHERN  
ROCKIES GIVEN THE INFLUENCE OF MARITIME AIR MASSES DURING THE  
PERIOD.  
 
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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