Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 270929 AFDBOX AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE TAUNTON MA 429 AM EST THU NOV 27 2014 .SYNOPSIS... STRONG LOW PRESSURE OVER NOVA SCOTIA WILL CONTINUE MOVING AWAY FROM NEW ENGLAND TODAY. HOWEVER SCATTERED LIGHT SNOW SHOWERS OR FLURRIES WILL DEVELOP LATER THIS MORNING AND AFTERNOON ACROSS THE REGION. A TROUGH OF LOW PRESSURE MAY PRODUCE ACCUMULATING SNOW ACROSS EASTERN MASSACHUSETTS LATE TONIGHT INTO FRIDAY. ELSEWHERE JUST LIGHT SNOW OR FLURRIES ARE EXPECTED. DRY BUT COLD WEATHER FOLLOWS FRIDAY NIGHT INTO SATURDAY. ANOTHER PERIOD OF LIGHT SNOW OR FLURRIES ARE POSSIBLE SATURDAY NIGHT. DRY AND MILDER WEATHER ARRIVES SUNDAY AND INTO EARLY NEXT WEEK. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 130 AM UPDATE... LOW PRES CONTINUES TO SHIFT NE INTO THE GULF OF MAINE AT 06Z. AREA OF MIXED RAIN/SNOW ALSO MOVES SLOWLY NE...BUT NOTING THAT IT HAS TENDED TO FILL IN ACROSS CENTRAL-W MA/S NH OVER THE LAST FEW HOURS. AS COLDER AIR WORKS IN ON DIMINISHING N WINDS...COULD SEE A LITTLE BIT MORE ACCUMULATION ESPECIALLY ACROSS S NH. ALSO...AS TEMPS FALL BACK OVERNIGHT TO THE MID TO UPPER 20S ACROSS THE INTERIOR WHERE THE HEAVIER SNOW HAS FALLEN...ANY AREAS THAT ARE STILL WET OR SNOW COVERED WILL FREEZE UP ESPECIALLY ON UNTREATED SURFACES. ALSO STILL NOTING N WINDS GUSTING UP TO 30-40 KT ACROSS CAPE COD AND THE ISLANDS AS LAST OF PRES GRADIENT AND LOW LEVEL JET MOVES OUT. HAVE UPDATED NEAR TERM FORECAST TO BRING CONDITIONS CURRENT. SHOULD SEE PRECIP TAPER OFF FROM SW-NE THROUGH REMAINDER OF THE OVERNIGHT. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 AM FRIDAY/... SEE LONG TERM SECTION. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... UPDATED 430 AM *** ACCUMULATING SNOW POSSIBLE LATE TONIGHT INTO EARLY FRI AFTERNOON ACROSS EASTERN MA FROM CAPE ANN TO BOSTON TO CAPE COD *** FRIDAY... INTERESTING SETUP FOR POSSIBLE NORLUN TYPE TROUGH ALONG THE EASTERN MA COASTLINE FROM CAPE ANN SOUTHWARD THROUGH THE CITY OF BOSTON... PLYMOUTH COUNTY TO CAPE COD TONIGHT INTO EARLY FRI AFTERNOON. ROBUST NORTHERN STREAM TROUGH MOVES ACROSS THE AREA TONIGHT AND FRI... INDUCING AN INVERTED TROUGH FROM OFFSHORE LOW NORTHWESTWARD BACK INTO EASTERN NEW ENGLAND. THE MID LEVEL TROUGH WILL PROVIDE MODEST SYNOPTIC SCALE LIFT AND WILL COMBINE WITH MESOSCALE FRONTAL SCALE FORCING FROM THE INVERTED TROUGH TO YIELD A NARROW BAND OF MODEST/APPRECIABLE QPF. BOTH THE NAM /00Z AND 06Z/ AND GFS HAVE AN AXIS OF QPF UP TO 0.25 INCHES FROM CAPE ANN SOUTHWARD INTO BOSTON AND THROUGH COASTAL PLYMOUTH COUNTY. EMBEDDED IN THIS AREA OF QPF IS A BULLSEYE OF 0.50 TO 0.60 INCHES OVER THE OUTER CAPE. ABOVE AVERAGE CONFIDENCE IN THIS QPF AS LOW LEVEL STREAMLINE ANALYSIS INDICATES STRONG CONVERGENCE VICINITY OF THE INVERTED TROUGH ALONG WITH STEEP LAPSE RATES AND NEARLY SATURATED WITHIN AND ABOVE THE AREA OF ASCENT. THUS THE FORCING SHOULD HAVE A STRONG RESPONSE AS INSTABILITY WILL BE REALIZED. IN ADDITION BUFKIT TIME SECTIONS FROM THE NAM AND GFS BOTH SUGGEST AT LEAST SOME OF THE LIFT WILL OCCUR IN THE DENDRITIC SNOW GROWTH REGION WHICH MAY PROVIDE A BIT OF BOOST TO SNOW TO LIQUID RATIOS...SAY 12-1 TO 15-1. PTYPE WILL BE SNOW AS TEMPS ALOFT ARE COLD FAIRLY COLD...-8C AT 850 MB BY 12Z FRI. HOWEVER ACROSS THE OUTER CAPE /EAST OF HYA/... DESPITE A NNE WIND BACKING TO NNW THIS SURFACE WIND TRAJECTORY WILL BE CROSSING OVER WATER TEMPS OF 45-50. BUFKIT SOUNDINGS INDICATE THIS BLYR WARMTH...WHICH MAY PARTIALLY ERODE VIA MODERATE TO HEAVY PRECIP /DYNAMICAL AND DIABATIC COOLING/. HOWEVER SNOW MAY STRUGGLE TO ACCUMULATE ON PAVED SURFACES HERE. SO WITH ALL OF THIS IN MIND THERE IS A MODERATE RISK /30-60 PERCENT/ OF ACCUMULATING SNOW ACROSS EASTERN MA LATE TONIGHT INTO EARLY FRI AFTERNOON. GIVEN MODEL QPF EARLY INDICATIONS ARE FOR A MODERATE RISK OF 2-4 INCHES OF SNOW...EXCEPT LESS ON THE OUTER CAPE GIVEN MARGINAL SURFACE TEMPS. LOW RISK /LESS THAN 30 PERCENT/ OF UP TO 6 INCHES OR SO IF INVERTED TROUGH LINGERS LONG ENOUGH OVER EASTERN MA. HOWEVER THESE INVERTED/NORLUN TROUGHS ARE VERY DIFFICULT TO PINPOINT ESPECIALLY 30-42 HRS IN ADVANCE. FOR EXAMPLE IF THE INVERTED TROUGH SHIFTS 25 MILES OR SO FARTHER EAST MOST OF THE SNOW WILL REMAIN OFFSHORE. THUS BIG BUST POTENTIAL. FORECAST CONFIDENCE NOT HIGH ENOUGH TO ISSUE A WINTER STORM WATCH AND STILL TOO MUCH UNCERTAINTY FOR AN ADVISORY. THUS TO HEIGHTEN PUBLIC AWARENESS AND CONVEY THE UNCERTAINTY WILL ISSUE A SPECIAL WEATHER STATEMENT. IT WON/T TAKE MUCH FOR THIS EVENT TO HAVE SOME IMPACT GIVEN THE NUMBER OF HOLIDAY TRAVELERS/SHOPPERS ON THE ROADS TONIGHT AND FRIDAY MORNING. SO STAY TUNED TO LATER FORECASTS AND DISCUSSIONS. THIS WEEKEND... QUIET AND COLD EARLY SAT THEN INCREASING CLOUDS WITH A CHANCE OF LIGHT SNOW OR FLURRIES LATE IN THE DAY OR AT NIGHT AS WEAK WAA PATTERN SETS UP. BY SUNDAY WARM FRONT LIFTS NORTH OF THE AREA WITH MILDER TEMPS...U40S TO L50S. NEXT WEEK... MILD TO START THE WEEK WITH HIGHS 50-55 MONDAY AHEAD OF AN APPROACHING COLD FRONT. CHANCE OF SHOWERS LATE MON/MON NIGHT AHEAD OF POLAR FRONT. MUCH COLDER TUE WITH 1040 MB HIGH OVER QUEBEC. NEXT CHANCE OF PRECIP MIDDLE OF NEXT WEEK AS WAA PATTERN SETS UP. COULD BE SOME MIXED PRECIP AS COLD AIRMASS MAY BE SLOW TO ERODE/DISLODGE. && .AVIATION /10Z THURSDAY THROUGH MONDAY/... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /THROUGH TONIGHT/...MODERATE CONFIDENCE. THROUGH 12Z...AREAS OF MVFR-IFR CIGS/VSBYS WILL CONTINUE THROUGH 08Z-10Z THEN SHOULD SLOWLY IMPROVE ACROSS N CT/RI INTO W MA TOWARD DAYBREAK. N WINDS GUSTING TO 30-35 KT THROUGH 08Z ACROSS CAPE COD AND THE ISLANDS THEN SHOULD DIMINISH. TODAY...LEFTOVER MVFR-IFR CIGS/VSBYS ACROSS CENTRAL/N MA INTO S NH SHOULD IMPROVE TO VFR BY MID MORNING. MAY SEE MVFR REDEVELOP ACROSS N CT/RI/SE MA DURING THE AFTERNOON ALONG THE E COAST ALONG WITH MORE CLOUDS MOVING NE INTO N CT/RI/S COASTAL MA. TONIGHT...MVFR CIGS MOVE ACROSS THE REGION. PRECIP DEVELOPS ACROSS E MA INTO RI...POSSIBLY AS FAR W AS KORH-KIJD...AS INVERTED TROUGH TAKE SHAPE NEAR THE COAST. AREAS OF MVFR-IFR VSBYS DEVELOP IN RAIN AND/OR SNOW. VSBYS SHOULD REMAIN MAINLY VFR ACROSS CENTRAL AND WESTERN AREAS...THOUGH PATCHY FOG MAY FORM LATE AT NIGHT. KBOS TERMINAL...HIGH CONFIDENCE TODAY...LOWER CONFIDENCE TONIGHT IN EXACT TIMING AS PRECIP DEVELOPS. KBDL TERMINAL...HIGH CONFIDENCE. OUTLOOK...FRIDAY THROUGH MONDAY...MODERATE CONFIDENCE. UPDATED 430 AM FRIDAY...MVFR OR IFR ACROSS EASTERN MA IN SNOW WITH IMPROVING TREND DURING THE AFTERNOON AND ESPECIALLY AT NIGHT. VFR ELSEWHERE. SATURDAY-SUNDAY...VFR WITH POTENTIAL MVFR LATE SAT/SAT NIGHT IN A PERIOD OF LIGHT SNOW OR FLURRIES. ALSO POTENTIAL FOR LOW LEVEL WIND SHEAR SUNDAY. MONDAY...COLD FRONT MOVES ACROSS NEW ENGLAND WITH SCATTERED SHOWERS. BRIEF MVFR CIGS/VSBYS IN ANY SHOWERS. CONTINUED SOUTHWEST WINDS AHEAD OF THE FRONT WITH 35-40 KNOTS AT 2000 FEET AGL AND POTENTIAL LOW LEVEL WIND SHEAR. && .MARINE... FORECASTER CONFIDENCE LEVELS... LOW...LESS THAN 30 PERCENT. MODERATE...30 TO 60 PERCENT. HIGH...GREATER THAN 60 PERCENT. .SHORT TERM /THROUGH TONIGHT/... TONIGHT...HIGH CONFIDENCE. GALE CENTER TRACKS JUST SOUTH OF NANTUCKET AND EAST OF OUTER CAPE COD BY MIDNIGHT. NE GALE FORCE WINDS WILL PUSH NE BETWEEN 05Z-07Z THEN WILL BACK TO N-NW THROUGH THE REMAINDER OF THE NIGHT AS THEY DIMINISH. SEAS APPEAR TO HAVE MAXED OUT AT 10-15 FT ON THE OPEN WATERS INCLUDING MASS AND IPSWICH BAYS AND UP TO 6 FT ON THE SOUTHERN OPEN SOUNDS...WHICH SHOULD SLOWLY SUBSIDE THROUGH THE REMAINDER OF THE NIGHT. LOW VSBYS IN RAIN EARLY...THEN WILL SLOWLY IMPROVE AS PRECIP WEAKENS. PRECIP WILL MIX WITH OR CHANGE TO SNOW SHOWERS BEFORE ENDING ACROSS THE SOUTHERN WATERS BY AROUND 08Z- 09Z...BUT COULD LINGER ON THE EASTERN WATERS THROUGH SUNRISE. THURSDAY...NORTHWEST WINDS GUST NEAR 25 KNOTS EARLY BUT DIMINISH THROUGH THE DAY. SEAS START THE DAY ROUGH...WITH HEIGHTS 8 TO 12 FEET ON THE EXPOSED WATERS...THEN DIMINISH THROUGH THE DAY. SMALL CRAFT ADVISORY WILL BE NEEDED ON MOST WATERS. OUTLOOK...THURSDAY THROUGH MONDAY...MODERATE CONFIDENCE. UPDATED 430 AM FRIDAY...LOW VSBY POSSIBLE IN SNOW ACROSS EASTERN MA WATERS. SNOW NEAR SHORE WITH RAIN OFFSHORE. VSBY IMPROVING IN THE AFTERNOON AND ESPECIALLY AT NIGHT. SATURDAY-SUNDAY... SOUTHWEST WINDS GUSTING TO 20 TO 25 KNOTS SATURDAY AND AROUND 25 KNOTS SUNDAY. SEAS WILL BE LESS THAN 5 FEET SATURDAY AND THEN BUILD TO 5 TO 6 FEET ON THE EXPOSED WATERS SUNDAY. A SMALL CRAFT ADVISORY MAY BE NEEDED SUNDAY. MONDAY...SOUTHWEST WINDS GUSTING 20 TO 25 KNOTS UNTIL THE COLD FRONT MOVES THROUGH. WINDS THEN SHIFT TO WEST-NORTHWEST BEHIND THE FRONT WITH SIMILAR GUSTS. SEAS ON THE EXPOSED WATERS WILL BE 5 TO 8 FEET. A SMALL CRAFT ADVISORY MAY BE NEEDED. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...NONE. MA...NONE. NH...NONE. RI...NONE. MARINE...SMALL CRAFT ADVISORY UNTIL 3 PM EST THIS AFTERNOON FOR ANZ231- 232. SMALL CRAFT ADVISORY FOR HAZARDOUS SEAS UNTIL NOON EST TODAY FOR ANZ233-234. SMALL CRAFT ADVISORY UNTIL 10 AM EST THIS MORNING FOR ANZ230. SMALL CRAFT ADVISORY UNTIL 9 PM EST THIS EVENING FOR ANZ235- 237. SMALL CRAFT ADVISORY UNTIL MIDNIGHT EST TONIGHT FOR ANZ250-251. SMALL CRAFT ADVISORY UNTIL 6 AM EST FRIDAY FOR ANZ254>256. && $$ SYNOPSIS...NOCERA NEAR TERM...WTB/EVT SHORT TERM...RLG LONG TERM...NOCERA AVIATION...NOCERA/EVT MARINE...NOCERA/RLG/EVT

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