Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 172344 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 644 PM EST Sun Dec 17 2017 .SYNOPSIS...
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A weak wave of low pressure will bring a period of light snow overnight into Monday morning, which may linger into the afternoon across northeast Massachusetts. Temperatures will be milder on Tuesday ahead of a cold front, then turn blustery and colder Wednesday into Thursday but with dry weather prevailing. Low pressure will likely pass to our west Friday night and Saturday, probably bringing mainly rain and a period of rather mild temperatures along with some wind. A period of unsettled weather may return sometime Christmas Eve into Christmas, but timing and precipitation types are uncertain.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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640 PM Update... Tonight into Monday morning... ***Light snow will likely impact the Monday morning commute*** Dry weather persists through late evening as mid level cloudiness continues to thicken. Temps will generally range from the teens to middle 20s through midnight. Increasing potential for light snow showers to develop during the overnight hours and move through southern New England during the morning commute. Low pressure over the Great Lakes will slowly begin to move towards the Northeast pushing the frontal system to our south northward as a warm front. Ahead of the front, isentropic lift within the WAA pattern will help provide just enough lift for precip to occur. Increasing moisture in the mid-levels will help saturate the snow growth region and with soundings keeping the profile below 0C anticipate snow showers. The lift does appear weak thus continued the mention of light snow showers late tonight and into the morning hours. One thing we will have to watch is the warm layer at 950mb. Both the EC and HRRR are in agreement of thermals which keeps this warm layer just south and west of our area, although it is close. Do not plan on issuing any winter weather advisories at this time for CT or RI. However with the cold temperatures overnight, any snow showers that do occur will accumulate on the roadways just in time for the morning commute. Will issue an SPS to highlight this concern for tomorrow morning. Anyone traveling should take it slow as roads can become slick. Overall snow accumulations will be around a coating to less than an inch. Snow should end by the mid-morning hours as the better lift moves northward.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Monday afternoon into Monday night... ***Low chance for spotty freezing rain across Northeast Massachusetts late Mon Afternoon*** Warm front to the south will begin to push into southern New England during the day on Monday. Despite southerly winds at the surface, 2m Temps from Hi-res guidance suggest that the front will struggle to push through keeping many sites in the low to mid 30s. May see some warming on the south coast to near 40F but it will be a struggle. Any lingering precip from the morning hours will be spotty and very light as the better lift continues to remain north of the region. However profile is still quite saturated so any forcing could help result in some showers. Depending on surface temps this could be snow or rain. Precip chance for the afternoon into the evening will linger across northeast MA as meso-low moving into coastal ME seems to develop some sort of inverted trough over that region. With this lingering moisture combined with increase 950mb warm layer, could see some freezing rain by later afternoon into evening hours. This could result in impacts to the evening commute in northeast MA. This is shown in BUFKIT soundings especially for BVY, LWM and BED. It will be close for BOS. Confidence is to low, and precip could be quite spotty so will hold off on winter weather adv for now. Something the overnight shift may want to look at. Shower chances decreases by the late evening resulting in a dry forecast for Monday night. Temperatures will remain steady as weak warm front pushes northward. && .LONG TERM /TUESDAY THROUGH SUNDAY/...
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Highlights... * Much milder Tue with mainly dry weather * Turning blustery and colder Wed into Thu with dry weather * Mainly rain Fri night/Sat with some wind and mild temps favored * Unsettled weather possible sometime Christmas Eve into Christmas Details... Tuesday... Much milder weather expected on Tuesday with 850T near 0C and southwest flow ahead of a cold front. High temps should reach into the upper 40s to near 50 with even some lower 50s possible in the coastal plain. Dry weather anticipated with the lack of synoptic scale forcing, but can not rule out a spot shower or two toward evening in western MA. Tuesday night and Wednesday... A cold front crosses the region region Tue night into early Wed with colder/blustery weather to follow. Mainly dry weather anticipated other than perhaps a few brief rain/snow showers across the east slopes of the Berkshires. Increasing wind will keep low temps Tue night mainly in the upper 20s to the lower 30s. High temps on Wed will generally be in the 30s to around 40, but northwest wind gusts of 25 to 40 mph will make it feel colder. Wednesday night and Thursday... Canadian high pressure builds into the region bringing dry but cold weather. Low temps Wed night should mainly be in the teens, but some single digits can not be ruled out in the normally coldest outlying locations. High temps on Thu should mainly be in the 30 to 35 degree range, but with less wind than on Wed. Friday and Saturday... Upper level ridging will be building across the southeast states as a shortwave trough lifts northeast towards the Great Lakes. While it is too early to completely lock in a solution...the given pattern and ensemble guidance strongly favors low pressure passing to our northwest putting us on the mild side of the storm. Timing still uncertain, but most guidance keeps the daytime hours dry with bulk of the rain Friday night and/or Saturday. Now there initially is still Canadian High pressure which slides off to the east, so can not rule out the low risk for a bit of snow/ice at the onset across the interior. Regardless, mainly rain is favored Friday night into Saturday across the entire region. In fact, temps could climb well into the 50s to near 60 for a time along with a period of strong southerly winds. Christmas Eve into Christmas... Very low confidence forecast in this time range. Upper level ridge with abnormally high height fields will be anchored off the southeast coast. Meanwhile, a dome of arctic air and well below normal temperatures will be invading much of the central states. This will place our region in the battle ground between these extreme airmasses. A couple waves of low pressure will likely track along the baroclinic zone and bring the risk for a period or two of precipitation sometime Christmas Eve into Christmas. Timing/ptypes and will depend on exactly where the baroclinic zone aligns. While snow is certainly an option especially at this time range...given strength of southeast upper level ridge would favor rain/ice. If we do have enough cold air for wintry precipitation, it might end up coming down shallow given rather high height fields which could possibly result in more of an ice threat than snow.
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&& .AVIATION /00Z MONDAY 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/...High confidence. Tonight...VFR with gradually lowering cigs through midnight. Mainly MVFR conditions overspread western MA/northern CT in light snow between 6z and 9z. These conditions may reach eastern MA and RI towards 12z. Monday...Widespread MVFR cigs with a few spots lowering IFR. Chance of light snow north of the Pike and rain south of the Pike. Precip will wind down by the afternoon. Lingering showers in Northeast MA could result in a wintry mix resulting in slick runways. Monday night...Improving conditions to VFR during the overnight. KBOS Terminal...Moderate confidence. Spotty light snow showers may arrive towards 12z and persist at times into the late Monday morning hours. May have to watch for spotty -fzdz after 20z. Low confidence if this will occur. KBDL Terminal...High confidence. Light snow will likely impact the terminal mainly between 6z and 10z Monday morning. Outlook /Tuesday through Friday/... Tuesday: Mainly VFR, with local MVFR possible. Windy with gusts to 30 kt. Tuesday Night: Mainly VFR, with local MVFR possible. Windy with gusts to 35 kt. Wednesday: VFR. Windy with gusts to 35 kt. Wednesday Night through Thursday: VFR. Breezy. Thursday Night: VFR. Friday: VFR. Breezy.
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&& .MARINE... 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. Tonight...Light winds and seas. Monday...Winds becoming SW and increasing in the afternoon but gusts below 20 kt. Seas below SCA. Chance of light snow changing to rain. Monday night...Dry weather with increasing winds and seas. Conditions remain below SCA. Outlook /Tuesday through Friday/... Tuesday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Tuesday Night: Moderate risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Wednesday: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Wednesday Night: Moderate risk for Small Craft Advisory winds with areas of gusts up to 30 kt. Local rough seas. Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Thursday Night: Winds less than 25 kt. Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Dunten/Frank NEAR TERM...Frank/Dunten SHORT TERM...Dunten LONG TERM...Frank AVIATION...Dunten/Frank MARINE...Dunten/Frank

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