Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 260924 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 424 AM EST WED NOV 26 2014 .SYNOPSIS...
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A DEVELOPING COASTAL STORM WILL TRACK NEAR OR OVER NANTUCKET THIS EVENING...THEN QUICKLY MOVING OUT TO SEA OVERNIGHT. THIS STORM WILL BRING A VARIOUS WEATHER IMPACTS TO THE REGION TODAY AND TONIGHT WITH HEAVY SNOW WELL INLAND...HEAVY RAIN AND STRONG WINDS ALONG THE COAST. WEATHER CONDITIONS WILL IMPROVE FOR THANKSGIVING DAY. HIGH PRESSURE BUILDS OVER NEW ENGLAND FRIDAY AND SHIFTS OFFSHORE OVER THE WEEKEND. A COLD FRONT SWINGS THROUGH NEW ENGLAND LATE SUNDAY NIGHT OR MONDAY.
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&& .NEAR TERM /UNTIL 7 AM THIS MORNING/...
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00Z MODEL GUIDANCE IN GOOD AGREEMENT ON TIMING OF PRECIP...COMING ONSHORE TO THE SOUTH COAST 6 AM TO 8 AM. THUS MOST OF THE MORNING COMMUTE WILL REMAIN DRY. COOLER AIR ADVECTING INTO THE REGION EARLY THIS MORNING ON LIGHT NNW FLOW. DEW PTS DOWN INTO THE MU20S ACROSS MUCH OF THE REGION.
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&& .SHORT TERM /7 AM THIS MORNING THROUGH 6 AM THURSDAY/...
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TODAY AND TONIGHT... *** WINTER STORM TRENDING CLOSER TO COAST RESULTING IN A RAIN/SNOW LINE FARTHER INLAND *** IMPACTS... * HEAVY SNOW WESTERN AND CENTRAL MA INTO SOUTHERN NH * STRONG WINDS SOUTHEAST MA AND SOUTHERN RI * HEAVY RAIN AND MINOR POOR DRAINAGE/URBAN FLOODING MUCH OF RI AND SOUTHEAST MA SYNOPTIC OVERVIEW AND MODEL PREFERENCES... 00Z MODEL GUIDANCE HAS TRENDED CLOSER TO THE COAST WITH THE SURFACE LOW PASSING OVER OR NEAR NANTUCKET. THIS SHIFT TO THE NORTHWEST MAY BE THE RESULT OF WIDESPREAD AND PERSISTENT UPSTREAM CONVECTION FROM OFFSHORE OF THE CAROLINAS EXTENDING SOUTHWEST ACROSS FL TO WEST OF CUBA. THIS CONVECTION MAY HAVE YIELDED A STRONGER DOWNSTREAM RIDGE OVER THE WESTERN ATLC RESULTING IN A STORM TRACK CLOSER TO THE COAST. REGARDING MODEL SOLUTIONS ECMWF AND GFS ARE FARTHEST NORTHWEST AND WARMEST. NAM CONSIDERABLY COOLER. FOR EXAMPLE THE NAM BUFKIT AT ORH OFFERS AN ALL SNOW EVENT WITH 9-12 INCHES. MEANWHILE THE GFS BUFKIT HAS MID LEVEL WARM INTRUSION WITH SNOW MIXING WITH OR CHANGING TO SLEET THEN BACK TO SNOW...BUT RESULTING IN ONLY 5 OR 6 INCHES. MORE OF THE SAME AT BDL. PATTERN RECOGNITION SUGGEST AXIS OF HEAVIEST SNOW SHOULD BE ALONG AND JUST NORTHWEST OF H7 LOW TRACK...WHICH MODELS AGREE WILL BE ACROSS NORTHWEST MA INTO SOUTHWEST NH. PTYPE AND SNOWFALL... GIVEN GOOD MODEL AGREEMENT ON TRACK OF H7 LOW FAIRLY CONFIDENT ON AXIS OF HEAVIEST SNOW ALONG AND NORTHWEST OF A LINE FROM BAF-CEF-FIT- ASH-MHT. A SWATH OF 6-12 INCHES IS EXPECTED ACROSS THIS AREA. SNOW WILL LIKELY BE HEAVY AT TIMES ACROSS THIS REGION FROM 18Z-02Z-ISH AS STRONG MID LEVEL FGEN COMBINES WITH SYNOPTIC SCALE LIFT TO PRODUCE SNOWFALL RATES OF 1-2 INCHES PER HOUR. EVEN A LOW PROB OF THUNDERSNOW AS DRY SLOT APPROACHES. GIVEN THERMAL PROFILES ARE ISOTHERMAL HEAVY WET SNOW MAY RESULT IN A RISK OF DOWN BRANCHES/SMALL LIMBS...INCREASING THE RISK FOR POWER OUTAGES ACROSS NORTHWEST MA INTO SOUTHWEST NH. SNOW GROWTH DOES NOT LOOK IDEAL SO EXPECTING SLR TO RANGE FROM 8-1 TO 12-1. FARTHER SOUTHEAST INTO NORTHERN CT-WORCESTER COUNTY OF MA AND INTO NORTHEAST MA...SNOW MAY MIX WITH SLEET FOR A TIME LATE THIS AFTERNOON AND EVENING BEFORE CHANGING BACK TO ALL SNOW LATER IN THE EVENING. THIS MIX OF SLEET WILL REDUCE SNOW TOTALS SOMEWHAT HOWEVER WILL ADD TO THE HAZARDOUS TRAVEL CONDITIONS. FARTHER SOUTH AND EAST INTO THE BOSTON TO PROVIDENCE CORRIDOR EXPECTING A COLD RAIN TO MIX WITH SLEET AND SNOW LATER IN THE DAY AND EVENING...YIELDING A SLUSHY MINOR ACCUMULATION POSSIBLE. NEVERTHELESS THIS WILL YIELD SLIPPERY TRAVEL ESPECIALLY 21Z-03Z WHEN PRECIP INTENSITY IS AT ITS GREATEST. FINALLY FOR SOUTHERN RI AND SOUTHEAST MA...MAINLY A WIND SWEPT RAIN STORM WITH MINOR POOR DRAINAGE/URBAN FLOODING AS RAINFALL TOTALS OF UP TO 2 INCHES POSSIBLE. OVERALL...NOT PLANNING ON CHANGING ANY HEADLINES DESPITE LOWERING SNOWFALL TOTALS. THE COMBINATION OF SNOW AND SLEET ON THIS BUSY TRAVEL DAY WITH PRECIP INTENSITY HEAVY AT TIMES IN THE AFTERNOON AND EVENING JUSTIFIES THE WARNINGS AND ADVISORIES DESPITE SNOW TOTALS POSSIBLY FALLING SHORT OF CRITERIA. THUS HEADLINES WILL BE MAINLY BASED ON IMPACTS. AS FOR SNOWFALL TOTALS...BASICALLY BLENDED THE WARMER 00Z MODEL SOLUTION WITH PREVIOUS SNOWFALL FORECAST WHICH RESULTED IN LOWER SNOW TOTALS AND AXIS OF HEAVIEST SNOWFALL FARTHER INLAND. HOWEVER IF 12Z GUIDANCE TRENDS CLOSER TO THE COAST DAY SHIFT WILL LIKELY HAVE TO LOWER AMOUNTS AND SHIFT AXIS OF HEAVIEST SNOW FARTHER INLAND. ONSET...GOOD MODEL AGREEMENT ON PRECIP COMING ONSHORE TO THE SOUTH COAST 6 AM TO 8 AM AND THEN RAPIDLY OVERSPREADING THE REMAINDER OF CT/RI AND MA RAPIDLY SOUTHWEST TO NORTHEAST 8 AM TO NOON. PRECIP INTENSITY...HEAVIEST 1 PM TO 8 PM FROM SOUTHWEST TO NORTHEAST. WINDS... A STRONG LOW LEVEL NORTHEAST JET WILL MOVE ACROSS RI AND SOUTHEAST MA INCLUDING CAPE COD AND THE ISLANDS AROUND 00Z. MODELS PROJECTING 50 TO 65 KT JET AT 925 MB. GFS IS THE MOST ROBUST. THIS COUPLED WITH STRONG PRES FALLS AND RELATIVELY WARM OCEAN WATERS PROVIDING A WELL MIXED BLYR WILL YIELD A MODERATE RISK OF 50 MPH WIND GUSTS FROM SOUTH COASTAL PLYMOUTH COUNTY/CAPE COD AND THE ISLANDS. GIVEN TRACK OF LOW IS FARTHER NW STRONG WIND FIELD NOW MOVES ACROSS COASTAL RI AND SOUTHEAST MA. THUS WILL EXPAND WIND ADVISORY TO THIS AREA. WINDS MAY DECREASE OVER THE ISLANDS FOR A TIME THIS EVENING AS LOW MAKES IT CLOSEST APPROACH...SOMEWHERE NEAR NANTUCKET. TIMING OF STRONGEST WINDS APPEAR 4 PM WED TIL 1 AM THU.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/... BIG PICTURE... SOUTHERN STREAM TROUGH MOVES UP THE COAST ACROSS NEW ENGLAND THURSDAY. NORTHERN STREAM SHORTWAVE THEN MOVES ACROSS THE REGION FRIDAY. THE FLOW THEN TRANSITIONS TO ZONAL OVER THE WEEKEND. THE LONG RANGE MODELS SHOW GOOD AGREEMENT ON 500 MB HEIGHTS THROUGH MONDAY AND THEN SMALL DIVERGENCE TUESDAY. THE GFS IS FASTER/FARTHER EAST WITH A CLIPPER SYSTEM CROSSING CANADA OVER THE WEEKEND. BUT THE MODELS COME MORE IN LINE WITH THE TRAILING COLD FRONT IN NEW ENGLAND SUNDAY NIGHT. THIS MAINTAINS AT LEAST MODERATE CONFIDENCE IN THE FORECAST THROUGH THE WEEKEND WITH DIMINISHING CONFIDENCE BY NEXT TUESDAY/DAY SEVEN. THE DAILIES... THANKSGIVING DAY... SOUTHERN STREAM UPPER TROUGH TRAILS THE WEDNESDAY STORM...AND MOVES OVER SOUTHERN NEW ENGLAND DURING THE DAY. MODEL CROSS SECTIONS FROM THE GFS AND ECMWF SHOW A DEEP SUPPLY OF HIGH-RH AIR AND SOME WEAK LIFT AS THE TROUGH MOVES ACROSS THE REGION. WE WILL EXPECT MOSTLY CLOUDS AS WELL AS A CHANCE OF PCPN. TEMPERATURE PROFILES SUGGEST SCATTERED SNOW SHOWERS INLAND AND SCATTERED RAIN SHOWERS IN RI/SOUTHEAST MASS. TEMPERATURE PROFILES SUPPORT MAX TEMPS IN THE 30S...EXCEPT LOWER 40S CAPE AND ISLANDS. WE STAYED CLOSE TO GUIDANCE THURSDAY NIGHT WITH MIN TEMPS IN THE 20S EXCEPT LOWER 30S CAPE AND ISLANDS. ANY WET SURFACES FROM THE DAYTIME WILL REFREEZE IN MOST LOCATIONS RESULTING IN TRICKY POST- MEAL TRAVEL ON ANY UNTREATED SURFACES. FRIDAY... NORTHERN STREAM SHORTWAVE RACES ACROSS NEW ENGLAND IN THE MORNING WITH LINGERING AIRMASS MOISTURE BUT WEAK LIFT IF ANY. THIS COULD HOLD THE CLOUDS IN A LITTLE LONGER FRIDAY MORNING. BUT IT MOVES OUT QUICKLY AND SURFACE HIGH PRESSURE BUILDS IN. SO THE TREND WILL BE FOR CLEARING SKIES. MIXING DEPTH WITH THE SUNSHINE IS EXPECTED TO BE RATHER SHALLOW...AROUND 950 MB OR MAYBE A LITTLE HIGHER. THIS WILL SUPPORT MAX TEMPS IN THE 30S AND WINDS GUSTING TO 15-20 KNOTS. HIGH PRESSURE MOVES OVERHEAD FRIDAY NIGHT. THIS WILL ALLOW TEMPS TO INITIALLY FALL WITH MOSTLY CLEAR SKIES AND LIGHT WINDS. BUT MOISTURE FIELDS SUGGEST SOME MID AND HIGH CLOUDS OVERNIGHT...AND POSSIBLY LOW CLOUDS MOVING UP FROM THE OCEAN TOWARD CAPE COD AND THE ISLANDS. FORECAST TEMPS ARE CLOSE TO GUIDANCE WITH 14-23 EXCEPT 24-30 ALONG THE SOUTH COAST. SATURDAY-SUNDAY...CONTINUED FAIR WEATHER OVER THE WEEKEND AS A WARM FRONT SWEEPS NORTH ACROSS NEW ENGLAND AND HIGH PRESSURE BUILDS OFFSHORE. THE COMBINATION SUGGESTS A WARMING TREND OVER THE WEEKEND WITH A 12C INCREASED IN TEMPS ALOFT BETWEEN SATURDAY AND SUNDAY. THE WARM FRONT WILL BRING VARIABLE SKY COVER...AS NOTED BY RH FIELDS ALOFT IN THE MODELS. SOUTHWEST WINDS AT 925 MB INCREASE TO 30 KNOTS SATURDAY AFTERNOON AND 30-40 KNOTS SATURDAY NIGHT AND SUNDAY. EXPECT SOME GUSTINESS TO OUR SURFACE WINDS EACH DAY. BUT LOW-LEVEL MIXING WILL BE LESS THAN IDEAL EACH DAY WITH BETTER MIXING SATURDAY AND LESS SUNDAY. MONDAY-TUESDAY...SHORTWAVE IN THE ZONAL FLOW WILL PUSH A COLD FRONT THROUGH NEW ENGLAND EITHER LATE SUNDAY NIGHT OR MONDAY. TIMING OF THE SHORTWAVE IN A ZONAL FLOW THIS FAR OUT IS IN QUESTION BUT THAT/S OUR BEST SHOT AT THIS TIME. LIMITED MOISTURE ALOFT TOGETHER WITH FAVORABLE JET DYNAMICS FROM A 125 KNOT JET...SO WE HAVE CHANCE POPS FOR RAIN/SNOW SHOWERS. HIGH PRESSURE THEN BUILDS DRY WEATHER FOR THE REST OF MONDAY AND TUESDAY. && .AVIATION /10Z WEDNESDAY THROUGH SUNDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /THROUGH TOMORROW NIGHT/...MODERATE CONFIDENCE. THROUGH 12Z...MAINLY DRY WEATHER WITH A LOW RISK OF RAIN MOVING ONSHORE INTO RI AND SOUTHEAST MA TOWARD 12Z. VFR WITH LIGHT NW WINDS BECOMING NORTH. AFTER 12Z...PRECIP OVERSPREADS THE REGION 12Z-16Z FROM SOUTH TO NORTH. PRECIP MAINLY RAIN ACROSS MOST OF RI /EXCEPT NORTH- NORTHWEST AREAS/ AND SOUTHEAST MA. HEAVY SNOW AND LIFR 18Z-00Z ALONG AND NORTHWEST OF A LINE FROM BAF-CEF-FIT-ASH-MHT WITH SNOWFALL RATES OF 1-2 INCHES PER HOUR POSSIBLE 18Z-00Z. SNOW MIXES WITH SLEET SOUTHEAST OF THIS AREA FROM BDL-ORH-LWM. STRONG NE WINDS UP TO 45 KT LIKELY AFTER 21Z OVER CAPE COD/ISLANDS AND COASTAL PLYMOUTH COUNTY. TONIGHT...HEAVY PRECIP LINGERS UNTIL 02Z/03Z ESPECIALLY EASTERN AREAS INCLUDING MHT. PRECIP TAPERS OFF AFTER 03Z AND ESPECIALLY AFTER 06Z FROM SOUTHWEST TO NORTHEAST. STRONG NNE WINDS TIL 06Z THEN BACKING TO NNW. KBOS TERMINAL...HIGH CONFIDENCE IN TRENDS BUT LOWER CONFIDENCE IN EXACT TIMING ESPECIALLY PTYPE. HEAVIEST PRECIP 20Z-03Z KBDL TERMINAL...HIGH CONFIDENCE IN TRENDS BUT LOWER CONFIDENCE IN EXACT TIMING ESPECIALLY PTYPE. HEAVIEST PRECIP 18Z-00Z. OUTLOOK...THURSDAY THROUGH SUNDAY...MODERATE CONFIDENCE THURSDAY...MVFR WITH SCATTERED RAIN/SNOW SHOWERS. DIMINISHING NORTHWEST WINDS. FRIDAY...VFR WITH NORTHWEST WINDS GUSTING 15-20 KNOTS. SATURDAY-SUNDAY...INCREASING SKY COVER BUT MAINLY VFR. LOW POTENTIAL FOR MVFR CIGS MOVING NORTH OFF THE OCEAN INTO CAPE COD AND ISLANDS. INCREASING WINDS AT 2000 FEET...REACHING SOUTHWEST 35-40 KNOTS...WITH LIGHTER SOUTHWEST WINDS AT SURFACE. && .MARINE...
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FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /THROUGH TONIGHT/...MODERATE CONFIDENCE. TODAY AND TONIGHT...GALE CENTER TRACKS OVER OR NEAR NANTUCKET EARLY THIS EVENING. THIS WILL RESULT IN A PERIOD OF NE GALES WITH A LOW RISK OF A FEW STORM FORCE GUSTS NEAR SHORE EARLY THIS EVENING. WINDS LIKELY EASE AROUND MIDNIGHT OVER CAPE AND ISLANDS AS LOW CENTER TRACKS ACROSS THIS AREA. SEAS BUILD RAPIDLY TODAY AND THIS EVENING. POOR VSBY IN HEAVY RAIN. WINDS BECOME NNW LATER TONIGHT AS THE GALE CENTER RACES NE TOWARD NOVA SCOTIA. OUTLOOK...THURSDAY THROUGH SUNDAY...MODERATE CONFIDENCE. THURSDAY... NORTHWEST WINDS GUSTING TO 25 KNOTS IN THE MORNING BUT DIMINISHING. SEAS START THE DAY 5 TO 11 FEET ON THE EXPOSED WATERS AND SUBSIDE TO 5 TO 6 FEET BY THE END OF THE DAY. SMALL CRAFT ADVISORY WILL BE NEEDED ON MOST WATERS. FRIDAY... LINGERING 5 FOOT SEAS ON THE OUTER WATERS. NORTHWEST WINDS WILL GUST 20 TO 25 KNOTS. A SMALL CRAFT ADVISORY MAY BE NEEDED ON SOME OF THE WATERS. SATURDAY-SUNDAY... SOUTHWEST WINDS GUSTING TO 25 KNOTS AND SEAS BUILDING TO 5 TO 6 FEET ON THE EXPOSED WATERS. A SMALL CRAFT ADVISORY MAY BE NEEDED.
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&& .TIDES/COASTAL FLOODING...
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HIGH TIDE OF CONCERN IS SHORTLY AFTER MIDNIGHT THURSDAY. STRONGEST WINDS AND PRESSURE FALLS OCCUR DURING LOW TIDE THIS EVENING WITH WINDS AND SURGE EASING TOWARD HIGH TIDE. THUS IMPACTS WILL BE LIMITED WITH VERY MINOR EROSION AND TIDAL FLOODING.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...WINTER STORM WARNING UNTIL 7 AM EST THURSDAY FOR CTZ002>004. MA...WINTER STORM WARNING UNTIL 7 AM EST THURSDAY FOR MAZ002>006- 008>012-026. WIND ADVISORY FROM 2 PM THIS AFTERNOON TO 3 AM EST THURSDAY FOR MAZ019>024. WINTER WEATHER ADVISORY UNTIL 7 AM EST THURSDAY FOR MAZ007- 013>016. NH...WINTER STORM WARNING UNTIL 7 AM EST THURSDAY FOR NHZ011-012- 015. RI...WIND ADVISORY FROM 2 PM THIS AFTERNOON TO 3 AM EST THURSDAY FOR RIZ005>008. WINTER WEATHER ADVISORY UNTIL 7 AM EST THURSDAY FOR RIZ001>003. MARINE...GALE WARNING FROM 3 PM THIS AFTERNOON TO 5 AM EST THURSDAY FOR ANZ230>237. GALE WARNING FROM 3 PM THIS AFTERNOON TO 7 AM EST THURSDAY FOR ANZ250-251-254>256.
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&& $$ SYNOPSIS...NOCERA NEAR TERM...NOCERA SHORT TERM...NOCERA LONG TERM...WTB AVIATION...WTB/NOCERA MARINE...WTB/NOCERA TIDES/COASTAL FLOODING...NOCERA

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