Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 112341 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 641 PM EST Mon Dec 11 2017 .SYNOPSIS... Low pressure in the Ohio Valley will move across New England Tuesday and northeast of the region Wednesday. It will bring a mixed bag of weather with snow northwest, a mix to rain central, and rain southeast late tonight and Tuesday. A shot of arctic air follows Wednesday and Thursday with a period of strong winds and bitterly cold wind chills. Another low pressure system may bring more snow to the region sometime in the Thursday night to Friday night timeframe, if it tracks close enough to the coast. Somewhat milder weather will arrive by the end of the upcoming weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 7PM update... The hi-res guidance is showing an initial burst of snow along route 2 around 6Z-9Z. Thus updated the forecast to account for this new trend. Otherwise, bulk of precipitation will be moving in around 12Z as previous discussion mentions. Forecast remains on track for this evening. Went ahead and updated sky cover and ceilings as mid level clouds are moving in sooner than previously forecasted. Previous discussion... A strong short wave trough seen on water vapor over IL will be rapidly moving east tonight and to eastern NY late tonight. Low pressure at the surface over Ohio will move into New York state overnight. Warm air advection cloudiness will increase across our region overnight and snow is likely to break out in northwest MA before daybreak. There is a chance that precipitation could reach as far as northern CT and central MA by daybreak. Although 850 mb temperatures are cold enough for snow, the 925 mb temperatures warm enough such that a few hours of freezing rain are possible in northern CT, northwest RI, and into southern Worcester and Middlesex Counties in MA within a few hours of daybreak. This could be a problem for the morning commute. We have expanded the Winter Weather Advisory southward and eastward a bit, to include Hartford, Tolland, Windham (in CT), northwest Providence County (in RI), and central and northwest Middlesex Counties (in MA). In these areas, a thin coating...less than one tenth of an inch...of ice is possible before daybreak. The Advisory remains in effect for the remainder of western and central MA. Lows tonight will be in the 20s except low to mid 30s Cape Cod and the islands. Light winds becoming southeast. Temperatures may begin to rise late in southern areas as southeast winds become established. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Tuesday... Any freezing rain should be short-lived but it could be a factor during the morning commute in the Hartford, Springfield, and Worcester areas, as well as the northwest suburbs of Providence. 925 mb temps warm very rapidly on strong southerly low level winds, so it should change to plain rain across most of southern New England during the morning. In fact, high temperatures will reach 50 degrees in RI and southeast MA! In the higher terrain of northern Worcester County and in the slopes of the Berkshires, snow will be moderate to heavy for a few hours in the morning, with total accumulations ranging from 2 to 4 inches, with local amounts of 5 or 6 inches in the extreme northwest corner of Franklin County, MA. Even there, some sleet and freezing rain may mix in during the afternoon. Southeast winds will become gusty...with up to 25-35 mph gusts possible along the coast. We have discounted the NAM, which has what appears to be way too strong of a LLJ of 80 kt at 850 mb and 50-60 kt gusts at the surface. All other models are more like 40-50 kt at 850 mb. Tuesday night... Winds shift to the west behind the departing storm system. However, as a vigorous upper level low approaches, scattered snow showers or squalls are possible, which could add some light accumulations, especially in western sections toward Wednesday morning. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... Wednesday... There is a chance of snow squalls continuing into Wednesday morning as an arctic front progresses across Southern New England. Very little snow accumulation is expected with these passing showers, likely up to an inch at most west of the Worcester Hills. Winds will pick up in the afternoon as there is an impressive upper level jet overhead. Models are in agreement with 40kts at 925mb mixing down to the surface Wednesday afternoon. The GFS suggests the strongest winds will be over the northern tip of the Cape and extend into Mass Bay. Wind gusts between 40 to 50 mph are not out of the question. Winds will likely peak by 00Z Thursday as the upper level jet sits directly over the region. Wednesday night temperatures will range in the teens due to the arctic airmass now over the region. With the combination of the arctic airmass and strong surface winds, wind chills are likely to hover near zero degrees overnight. With minimal cloud cover as well, radiational cooling will add to the low apparent temperatures. Thursday and Friday... Strong winds will continue into Thursday morning but begin to dissipate throughout the afternoon and evening. Both the ECMWF and NAM point towards a weak system that brings light snow to the islands and southern coast of New England Thursday afternoon. The system will likely not linger off the coast for very long, resulting in minimal snow accumulations, if any at all. The arctic airmass remains over the region through Thursday and Friday resulting in much below normal afternoon temperatures. With the winds diminishing by Thursday evening, wind chills should not be an issue, however overnight temperatures will continue to range in the teens across much of the region. Friday night and Saturday... A coastal low is expected to clip the region Friday/Saturday resulting in periods of heavy snow along the 95 corridor. Unfortunately, the models are not in agreement with timing or position for when it does make its way up to Southern New England. Going with guidance from the ECMWF and NAM, precipitation will push north across the region starting at 18z. As the low moves further northeast, east of the 95 corridor will likely see the most accumulation. The coastal low is expected to push offshore by Saturday afternoon. Sunday... A ridge builds in Sunday morning behind the coastal low. Winds will turn to the southwest, advecting warmer temperatures into the region by midday. Dry and seasonable temperatures will continue through early next week. && .AVIATION /00Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/... Tonight...Moderate confidence. VFR to start, will give way to MVFR early AM Tue as CIGS lower and light SN/FZRA moves in mainly after 06Z along and north of route 2. SN accums would be light. Light winds shift around to the E, except SE along the coast. Tuesday...Moderate confidence. Mixed MVFR and occasional IFR conditions in a mix of SN/FZRA giving way to all RA through sunrise into midday Tue. Risk for NW MA to remain SN long enough for accums to reach 3-6 inches with little or no snow accumulation southeast of a Hartford to Boston line. Period of FZRA before the change to RA. Conditions improve after 20Z. Winds gusting to 20-30 kt along the coast. Tuesday night...Moderate confidence. MVFR ceilings and scattered snow showers moving from west to east across the region. Local IFR in any heavier snow showers, especially in western sections. West winds gusting to 20-25 kt at times. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Potential for wintry mix between 12Z-14Z. Outlook /Wednesday through Saturday/... Wednesday: Mainly VFR, with local IFR possible. Windy with gusts to 35 kt. Slight chance SHSN. Wednesday Night: VFR. Strong winds with local gusts to 40 kt. Thursday through Thursday Night: VFR. Breezy. Friday: Mainly VFR, with local IFR possible. Chance SN. Friday Night: Mainly VFR, with areas IFR possible. Breezy. Chance SN. Saturday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/... Tonight...High confidence. Winds are slowly diminishing. Seas will slowly subside...to below SCA criteria over the southern waters by this evening. Quiet boating weather tonight, but that will be very temporary. Tuesday...Moderate confidence. Winds gradually shift around to the SE. Gusts 25-30 kt expected on the S waters with 35-40 kt possible on the E waters. Gale Warnings are in effect for the eastern waters with Small Craft Advisories posted for all other waters. Rough seas of up to 5 to 10 ft on the outer waters. Tuesday night...Winds shift to the southwest to west. Winds still gusting to 25-30 kt and seas still quite rough, especially over the southern outer waters. Outlook /Wednesday through Saturday/... Wednesday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 14 ft. Slight chance of snow showers. Visibility 1 to 3 nm. Wednesday Night: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 14 ft. Thursday: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Local rough seas. Local visibility 1 to 3 nm. Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Friday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of snow. Areas of visibility 1 to 3 nm. Friday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Chance of snow. Visibility 1 to 3 nm. Saturday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Local visibility 1 to 3 nm. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Weather Advisory from 4 AM to 10 AM EST Tuesday for CTZ002>004. MA...Winter Weather Advisory from 4 AM to 1 PM EST Tuesday for MAZ005-010>012. Winter Weather Advisory from 4 AM to 4 PM EST Tuesday for MAZ002>004-008-009-026. RI...Winter Weather Advisory from 4 AM to 10 AM EST Tuesday for RIZ001. MARINE...Small Craft Advisory from 9 AM Tuesday to 6 AM EST Wednesday for ANZ231>234. Small Craft Advisory from 1 PM to 7 PM EST Tuesday for ANZ230- 236. Small Craft Advisory until 6 AM EST Wednesday for ANZ235-237- 255-256. Gale Warning from 10 AM to 7 PM EST Tuesday for ANZ250-251-254. && $$ SYNOPSIS...Correia/GAF NEAR TERM...Correia/GAF SHORT TERM...GAF LONG TERM...Correia AVIATION...Correia/GAF MARINE...Correia/GAF

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