Area Forecast Discussion
Issued by NWS Boston, MA

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289 FXUS61 KBOX 041452 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 952 AM EST Sun Dec 4 2016 .SYNOPSIS...
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High pressure today with dry, cold conditions as winds diminish. Light snow Monday morning will bring a minor accumulation before tapering off to a mix of light rain and snow in the afternoon. Mainly dry conditions expected Monday night into Tuesday with high pressure. Low pressure off the mid Atlantic coast may bring some mixed light rain and/or snow into Southern New England Tuesday night into Wednesday night. A polar front crosses the region Thursday with rain showers possibly changing to snow showers. Very windy and cold conditions forecast for Friday and next Saturday with wind chill indices in the single digits and teens Friday night.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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10 am update... High pressure building in from the W as heights rise aloft. Should continue to see a downward trend in NW winds with gusts in excess of 20 mph over the E-half of S New England initially. Increasing subsidence across the region, should see clouds clear out. Still a decent cold airmass aloft given residual cyclonic flow out of the NW ahead of aforementioned ridging. Near-seasonable conditions, just a tad below, with highs around the upper 30s to low 40s seems reasonable for today. Overall pleasant and dry, more tolerable with less wind.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
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Snow Potential... Good model agreement on snow overspreading CT and western-central MA between 09z-12z...then into RI and eastern MA 12z-15z. Here are a few limiting factors that will keep snowfall potential low... 1) Short wave trough is very progressive, thus short duration of snowfall 2) Deep layer moisture is brief as well 3) PoPs from guidance are only high chance/low likely. This could be a potential red flag. Prefer to see guidance offering category PoPs if expecting accumulating snow. 4) Forcing for ascent is fairly weak and brief in the snow growth region (-10c to -18c) with dry air entering this layer rapidly from 15z-18z. Given this not expecting large snow ratios. 5) Short wave trough is deamplifying along with weakening wind fields with time as it approaches and moves across southern New England. This will limit forcing for ascent. 6) Warm air at 925 mb surging northward will likely change snow to rain toward midday across CT/RI and south of the MA turnpike. This will also limit snowfall potential. While boundary layer wet bulb temperatures are below freezing...precipitation may be too light to take advantage of evaporative cooling or from melting precipitation. Given all of the above factors will play this portion of the forecast conservative for now. Potential snowfall looks to be from a coating to an inch for most locations. A few locations in the higher terrain of CT/MA will have a low risk for up to 2 inches. Overall not a high impact event. Best chance of roads briefly becoming snow covered will be across CT/western-central MA including the Greater Hartford-Springfield areas before snow shield weakens as it moves eastward. Given these factors above will hold off on any headlines or statements for the moment. Temperatures... Temps will fall rapidly this evening with sunset given cold/dry airmass in place combined with clear skies and light winds. Thus blended some of the colder MOS guidance to account for this. Then clouds arrive around or shortly after midnight resulting in temps leveling off or perhaps rising a few degs toward daybreak. Temps begin to rise late Mon morning and afternoon as blyr winds become light SE. Winds... Winds will be light given weak pres gradient as feeble low pres tracks south of New England.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * Mixed precipitation possible late Tuesday night and Wednesday * Very strong front blasts across the region Thursday * Windy and very cold into next weekend with strong gales over the waters Monday night...High confidence. Expecting quiet conditions as high pressure builds across the region. Skies becoming mostly clear, except for a few lingering clouds across the E slopes of the Berkshires. N winds will be a bit gusty early along E coastal areas, then will diminish as the high takes over. With the lighter winds, should see some radiational cooling especially in the normally colder locations. Temps will fall back to the mid and upper 20s across most locations, ranging to the 30s along the immediate coast. Tuesday...Moderate confidence. High pressure ridge extending from a central across Quebec down the eastern seaboard will lift NE during the day. Winds become light NE-E. Weak low pressure moving NE out of the SE U.S. will bring some clouds across the region during the afternoon. Overrunning moisture will push NE toward the region after 18Z, so carried just chance POPs across N CT into SW RI by sunset. Some question on the timing and extent of the moisture into the region, however. Expect highs in the mid and upper 30s across the higher inland terrain, ranging to the lower-mid 40s along the coast. Tuesday night through Wednesday night...Moderate confidence. Fast moving weakening H5 short wave in the SW flow behind the exiting ridge will cross the region Tuesday night, with weak low pressure off the mid Atlantic coast. With onshore easterly flow, will see light precip starting off as light snow, then mixing with or changing to rain across the coastal plain with the light but steady onshore winds. As the short wave lifts NE into Wednesday morning, the surface low off the mid Atlantic will shift E well south of the region taking its moisture field offshore. So, will see precip become rather spotty by Wednesday evening. Temperatures on Wednesday will rise to the upper 30s to mid 40s across most areas, but remaining a bit cooler across the higher inland terrain. Looks like precip should change to mainly light rain by midday Wednesday. By Wednesday night...most models and ensembles start to bring more moisture to the region after midnight. So, brought chance POPs back in for now. QPF amounts remain low with lack to deep moisture field. As temps fall back, any mixed rain and/or snow across the interior will change back to light snow, with the best chance across the E slopes of the Berkshires. Thursday and Thursday night...Moderate confidence. Timing and track differences continue as a polar front wraps around the cutoff low pressure across Hudson Bay. A digging H5 long wave trough, bringing surge of very cold air from western Canada and Alaska, will work eastward. Will see southerly winds ahead of the front Thursday, but exact timing of the frontal passage in question. GFS tending to be faster with this feature than the ECMWF, which was similar to the previous forecast. Continued with a model blend this forecast. The front should pass through Thursday night, accompanied by a chance of snow showers across most of the region, except rain in southern RI, Cape Cod, and the Islands. Lows 25 to 30 except mid to upper 30s Cape Cod and Islands. Friday and Saturday...Moderate confidence. Colder air will sweep in across the region Friday as W-NW winds quickly increase. Models differ with the development of strong low pressure over the Maritimes during this timeframe. However, with the strong pressure gradient, expect winds to gust up to 25-35 kt, highest along the east coast, which looks to continue through Saturday. May see gusts around 40 kt along the coastal waters Friday night and Saturday. May also see lingering snow showers across the E slopes of the Berkshires, as well as ocean effect snow showers off the coast. With the strong cold air advection moving in, expect highs on Saturday to run up to 10 degrees below seasonal normals. Will also see wind chill values Friday night into early Saturday morning down to the single digits and teens. && .AVIATION /15Z SUNDAY THROUGH THURSDAY/...
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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 Monday/...High confidence. Today... VFR. Low-end VFR cigs around 4-5 kft dissipating W to E as are NW winds initially around 20 kts for the E-half of S New England terminals. Tonight... VFR and light winds. MVFR in SN overspreading CT and western- central MA between 09z-12z...holding off til 12z-15z across RI and eastern MA. Monday... MVFR to IFR mix. -SN in the morning, tapering off in the afternoon. -SN mixing with and/or changing to -RA along the S coast, possibly N along the I-95 corridor. Light snow accums possible on runways, coating to an inch with highest amounts over N/W high terrain. Low risk +2 inches over N/W CT and MA. Improving to VFR towards sunset W to E with MVFR persisting over RI and E MA. KBOS TAF... VFR and diminishing NW winds today. MVFR with -SN 12z-15z Monday. Snow accumulations possible from a coating to half an inch. KBDL TAF... VFR and diminishing NW winds today. MVFR with -SN 9z-12z Monday. Snow accumulations possible from a coating to an inch. Low risk of 2 inches. Outlook /Monday Night through Thursday/... Monday night...VFR. Mainly clear skies, except lingering clouds early across the E slopes of the Berkshires and across E coastal Mass through around midnight. Light NW winds. Tuesday...High confidence. VFR. Tuesday night through Wednesday night...Low to moderate confidence. MVFR to local IFR ceilings in light rain RI/SE Mass, a mix of rain/snow northern CT, central and northeast Mass, and light snow northwest MA. May briefly change over to all rain across most areas late Wednesday morning into the afternoon. Thursday...Low to moderate confidence. Mainly MVFR ceilings in areas of light rain showers ahead of approaching polar front. Depending on timing, rain showers could change to snow showers with local IFR conditions in western MA late in the afternoon.
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&& .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 Monday/... Today... Gusty NW winds diminish as the day progresses allowing small craft advisories to conclude through the day, lingering the longest over the E outer waters. Tonight... Light winds as high pressure crest over the waters. Dry weather and good visibility. Monday... Light SE winds as weak low pressure tracks near the Southern New England coast. Outlook /Monday Night through Thursday/...Moderate confidence. Monday night through Wednesday night...Winds and seas remain below small craft criteria for most of the waters. NW winds Mon night will shift to E, gusting up to 20 knots at times. Seas may build to near 5 ft over the southern outer waters by Wednesday night. Thursday...Small craft advisories will likely be needed. Winds will shift to the S-SE and may gust up to 25 to 30 kt by late Thursday afternoon. Winds may shift to SW toward Thu evening. Seas will be building to 5-7 ft over the outer waters. Attention mariners...Expect strong W-NW gales with some potential for storm force gusts are forecast to develop Friday into Saturday. Stay tuned for the latest forecast updates.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 AM EST this morning for ANZ230>237-251-256. Small Craft Advisory until 4 PM EST this afternoon for ANZ250- 254-255. && $$ SYNOPSIS...Nocera/EVT NEAR TERM...Nocera/Sipprell/EVT SHORT TERM...Nocera LONG TERM...EVT AVIATION...Nocera/Sipprell/EVT MARINE...Nocera/EVT

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