Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 100839 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 339 AM EST Sun Dec 10 2017 .SYNOPSIS... Mainly dry and cool conditions are expected Sunday 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. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Local OBs and MSAS suggest the low pres near 990hPa and just S of Nova Scotia as such the strongest low-mid lvl f-gen continues to pull to the E with it, snowfall rates having dropped significantly, with what little is left having vsbys +6sm. Meanwhile, dry air continues to filter in from the S aloft, mainly above H6, with enough lower lvl moisture to yield some light SHSN continuing over the next few hours, ending especially once BL mixing is able to dry out the near sfc moisture. Also, given the dry-over-moist sounding profile, cannot rule out some occasional freezing drizzle, continuing the risk for slippery conditions where roads are untreated. Otherwise today, clearing and drying expected in advance of the primary upper lvl shortwave which will move through overnight. CAA aloft will allow H85 temps to drop to near -10C by 00Z this evening, which combined with a new snowpack across much of interior S New England will keep high temps mainly in the low- mid 30s, near 40 where little to no snowfall fell. Breezy, as the CAA will allow tapping of the W LLJ which is near 30 kt. Gusts to around 25mph can be expected. While there is a low risk for an isolated SHSN, especially as moisture associated with the overnight wave passage approaches, given the initial drying and the fact that most of the moisture associated with the wave is trapped aloft, so will maintain NIL POPs. && .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 /08Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/... Through 12Z...High confidence in trends, lower confidence in exact timing. A mix of IFR/MVFR conditions in light SN most areas (except SE MA/RI where RA will transition briefly to SN before ended) will continue through about 08Z, then gradually give way to VFR and no SN between 08Z and 12Z. However, occasional FZDZ will continue through about 12Z except where current RA, dissipating as CIGs rise. Today into tonight...High confidence. Mainly VFR after early MVFR conditions dissipate early this AM. A few lower VFR CIGS tonight. W winds will gust 20-25 kt at times late today. Tomorrow...High confidence. Mainly VFR. W winds 10-15 kt. KBOS Terminal...High confidence in TAF trends. Remnant MVFR conditions dissipate as SN ends this AM. Some FZDZ lingers through 11Z otherwise improvement may be off a bit in TAF. KBDL Terminal...High confidence in TAF trends. Outlook /Monday Night through Thursday/... Monday Night: Mainly VFR, with local IFR possible. Chance SN. Tuesday: Mainly IFR, with areas MVFR possible. Breezy. RA, SN. Tuesday Night: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHSN. Wednesday: VFR. 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. && .MARINE... 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 overnight, 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. && .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...Doody SHORT TERM...Doody LONG TERM...Frank AVIATION...Frank/Doody MARINE...Frank/Doody is the U.S. government's official web portal to all federal, state and local government web resources and services.