Area Forecast Discussion
Issued by NWS Boston, MA

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494 FXUS61 KBOX 101852 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 152 PM EST Sun Dec 10 2017 .SYNOPSIS...
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Mainly dry and cool conditions are expected through 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 /THROUGH TONIGHT/...
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Lake-effect clouds were spilling over the Berkshires into western and central MA. Expecting a mid level shortwave to arrive tonight, which will only spread more clouds from west to east across southern New England, especially after midnight. As such, not expecting good radiational cooling conditions. That said, min temperatures tonight should be below normal. Fairly dry air below 800 mb, so dry weather will prevail for much of the interior. A little different story towards the coast, and coastal waters. The arrival of colder air over the still relatively warm ocean will kickstart the ocean-effect process. This will be mainly in the form of clouds, but cannot dismiss the possibility for some showers around the Cape and islands, including Block Island. A west wind direction would place the greatest risk for any showers across the southern coastal waters.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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Mid level shortwave departs during Monday morning, followed by a brief period of higher pressure. A nearly stationary front may sag far enough south to reach portions of southern New England late Monday into Monday night. Mainly dry with clearing sky once any lingering morning showers move offshore. High temperatures remaining below normal. A low pressure over the Great Lakes starts to exert more influence on our weather late Monday Night. Another case of increasing clouds after midnight, with a risk for some precipitation late. Given low temperatures below freezing across pretty much all of southern New England, light snow would be expected over land, with the possibility of some rain over the ocean waters. Thinking around one inch or less across southern New England through Monday night. It will all come down to timing. A faster arrival would give more time for snow to accumulate before daybreak. Slower timing would mean even less snow. At this point, the majority of any precipitation from this low pressure would occur after daybreak Tuesday. Some impact on the Tuesday morning commute is expected, especially from Worcester county west.
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&& .LONG TERM /TUESDAY THROUGH SATURDAY/...
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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... Tuesday... The main concern 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.
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&& .AVIATION /18Z SUNDAY THROUGH FRIDAY/...
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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 Night/... Through Tonight...High confidence. Mainly VFR despite a broken deck of mid level cloudiness. Areas of low end VFR west of KFIT=KORH-KIJD. Brief marginal MVFR conditions in a spot snow shower possible late. Tomorrow...High confidence. Mainly VFR. Tomorrow Night... High confidence. Mainly VFR, with local MVFR- IFR possible toward daybreak as SN moves into the region, with some RN along the coastal plain. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Tuesday through Thursday/... 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 Night/...High confidence. Gusty west winds gradually diminish Monday afternoon. However, rough seas will take longer to subside, especially across the southern coastal waters, where the fetch will be longer. Therefore, most Small Craft Advisories will continue into tomorrow. Chance for showers, especially across the southern coastal waters tonight into Monday morning, then again late Monday night. Outlook /Tuesday through Thursday/... 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...Belk/Frank NEAR TERM...Belk SHORT TERM...Belk LONG TERM...Frank AVIATION...Belk/Frank MARINE...Belk/Frank

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