Area Forecast Discussion
Issued by NWS Boston, MA

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798 FXUS61 KBOX 101529 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1029 AM EST Sun Dec 10 2017 .SYNOPSIS...
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Mainly dry and cool conditions are expected this afternoon and Monday. Low pressure will approach from the west late Monday night into Tuesday. This will likely bring a period of accumulating snow mainly to the northwest of the Boston to Providence corridor, while southeast New England should be mild enough for mostly rain. A shot of arctic air follows Wednesday and Thursday along with a period of bitterly cold wind chills. Another low pressure system may bring more snow or mixed precipitation to the region sometime Thursday night/Friday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Last of the snow moved offshore earlier this morning. clouds continuing to diminish over land, but persist across the eastern outer coastal waters. Plenty of sunshine expected to help the melting process this afternoon. Minor tweaks to bring the forecast back in line with observed trends. Previous Discussion... There were just a few lingering snow flurries across the southeast New England coast early this morning, which should end shortly. Main concern through mid morning are untreated roads/walkways will be slippery with patchy black ice. These conditions should improve later this morning and afternoon as temps rise above freezing. A mixture of sun and clouds is anticipated with high temps well up into the 30s to near 40. Gusty west winds will make it feel a bit colder.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Overnight... Upper lvl shortwave, linked to weakening cold front will approach through the overnight hours. As mentioned above, most of the moisture associated with this wave/front is aloft and minimal, so mainly increase in clouds is expected. Cannot rule out an isolated SHSN, however these will be few and far between, and relatively light. Once again, leaned on NIL to low end slight chance POPs. Mins will be limited thanks to increase in cloud cover overnight, but should still dip below freezing, into the mid 20s thanks to a cool start. Mon... High pres builds in behind the weakening wave, allowing winds to once again shift to the W. Mainly dry after any lingering SHSN early. Highs once again remain cooler than they otherwise could thanks to cool air aloft and lingering snowpack. Expecting mainly mid 30s, with a few spots near 40 where less SN is observed. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * Accumulating snow may impact Tue AM rush hour...mainly northwest of the BOS-PVD corridor and especially interior northern MA * Arctic air follows Wed/Thu along with a period of bitterly cold wind chills * Some more snow or mixed precipitation possible late Thu night/Fri Details... Monday night and Tuesday... The main concern late Monday night into Tuesday revolves around snow potential and possible impact to the morning rush hour...mainly north and west of the Boston to Providence corridor. Northern stream shortwave energy will be diving south towards the Great Lakes along with an initial surface low tracking to our northwest. The result will be a decent southerly LLJ developing which will increase the forcing for ascent. The antecedent airmass is cold, but given southeast winds blowing off the ocean in early December is not usually a recipe for much snow along the coastal plain. While a brief period of snow can not be ruled out, unless guidance changes significantly would be tough to get more than an inch. The forecast is more complex to the northwest of the Boston to Providence corridor and particularly across interior northern MA. The cold antecedent airmass should result in at least a period of snow, but whether accums are minor or several inches hinges on a few things. Some of the 00z guidance has trended a bit quicker with secondary coastal development, which would slow down or limit the mid level warm surge. A very small change in thermal profiles can make a difference from some areas receiving an inch vs 5 inches of snow. While this remains uncertain, the potential for several inches of snow is highest across interior northern MA. Regardless, the Tuesday morning rush hour will likely be impacted to some degree. Will also have to watch for a band of ice in the transition zone as low level cold air will be tough to scour out. The bulk of the precipitation should be over by late afternoon. Wednesday and Thursday... The main story will be a shot of arctic air as a deep upper trough sets up over New England. While dry weather will dominate other than a brief passing snow shower or two, temperatures will be well below normal. Lows should be between 5 and 15 above and highs only in the 20s. It also should be rather windy for a time which should result in wind chills dropping to between 5 above and 10 below zero late Wednesday night/Thursday morning. Thursday night and Friday... Low confidence at this point given time range and model disagreement. However, will have to watch for shortwave/low pressure system that may bring a period of snow and/or mixed precipitation to the region. Next Weekend... It looks like we should see some moderation in temps by the end of next weekend, but the extent of that and low long it lasts is unknown at this point. && .AVIATION /16Z 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/... Today...High confidence. VFR, but some lingering FEW/SCT clouds between 1000-1500 feet across the outer Cape and Nantucket. Lower clouds continue to move offshore late this morning. Westerly wind gusts of 20 to 25 knots develop into this afternoon. Tonight...High confidence. Mainly low end VFR despite a broken deck of mid level cloudiness. Brief marginal MVFR conditions in a spot snow shower possible late. Tomorrow...High confidence. Mainly VFR. W winds 10-15 kt. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Monday Night through Thursday/... Monday Night: Mainly VFR, with local MVFR-IFR possible toward daybreak as SN moves into the region with some RN along the coastal plain. Tuesday: Mainly IFR, with areas MVFR possible. Breezy. RA, SN. Tuesday Night: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHSN. Wednesday: Mainly VFR, with areas MVFR possible. Windy with gusts to 35 kt. Slight chance SHSN. Wednesday Night: VFR. Strong winds with local gusts to 40 kt. Thursday: VFR. Windy with gusts to 30 kt.
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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/...High confidence. W winds will briefly shift to the SW tonight, but gusts to 25 kt are likely right into early Mon. Meanwhile seas, which currently run 8-9 ft offshore will linger, only diminishing as winds recede on Mon. Therefore, most small craft advisories will continue into tomorrow. Outlook /Monday Night through Thursday/... Monday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain. Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Rain. Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Slight chance of rain showers, slight chance of snow showers. Wednesday: Moderate risk for gale force winds with gusts up to 40 kt. Areas of rough seas. Slight chance of snow showers. Wednesday Night: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 11 ft. Slight chance of snow showers. Thursday: Low risk for gale force winds with gusts up to 35 kt. Local rough seas.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 1 PM EST Monday for ANZ231>235-237- 250. Small Craft Advisory until 7 AM EST Monday for ANZ251. Small Craft Advisory until 7 PM EST Monday for ANZ254>256. && $$ SYNOPSIS...Frank/Doody NEAR TERM...Belk/Frank SHORT TERM...Doody LONG TERM...Frank AVIATION...Belk/Frank/Doody MARINE...Frank/Doody

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