Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 171555 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1055 AM EST Fri Nov 17 2017 .SYNOPSIS... Intensifying low pressure over the Maritimes yields a dry but blustery and chilly day across New England. High pressure crests across the area tonight providing dry but cold weather. Strengthening low pressure will push across the St Lawrence River Valley this weekend as gusty southwest winds develop Saturday afternoon and night. A cold front will cross the region by Monday morning, with another shot of cold and blustery conditions. Dry conditions will prevail from Monday through Thanksgiving. Temperatures will fluctuate daily, from mild to below average in the fast flow aloft. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... no major changes to the forecast this morning, but did bring it back in line with observed trends. The main concern remains the winds. Decided to hold off on a Wind Advisory for this morning. Wind speeds are just beneath criteria and the spotter reports are only indicating isolated minor damage. Previous Discussion... Closed mid level low and surface cyclone over Nova Scotia continues to intensify today given trough amplification and associated height falls. This results in modest CAA into southern New England with 850 temps lowering to -6C this morning, about -1 standard deviation colder than climo. This combined with tight pres gradient will result in a chilly morning across the region with NW winds gusting up to 35 mph. Cold air advection peaks this morning then eases this afternoon as mid level trough moves offshore replaced by height rises across the region. Thus not as windy this afternoon. However temps will only rebound to 40-45, upper 30s across the high terrain, almost 10 degs cooler than normal. Scattered to broken cold air advection strato-cu this morning will give to mostly sunny conditions this afternoon as temps begin to warm aloft in response to height rises. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... 330 AM update... Tonight... Ridge of high pres builds across the area from west to east, resulting in a cold night especially outside the urban areas as mostly clear skies combine with light winds and a very dry airmass. For whatever reason MOS has been running too cold in these radiational cooling events this past month so we will follow a model blend here to offset the colder MOS guid. Nonetheless most locations fall into the 20s tonight, upper teens northwest MA and closer to 30 for Boston. Will have to watch mid and high clouds spilling into the area late tonight, which may have an impact on temps with mins possibly not quite as cold. Saturday... Chilly start to the day but low level WAA commences with increasing SSW winds during the afternoon and especially late in the day. Some morning sunshine thru high clouds possible, but will fade behind increasing clouds during the afternoon as mid level trough and 985 mb surface cyclone exits Great Lakes. All global guidance including ensembles keep dry weather across the entire region thru 18z Sat. Thereafter showers overspread the area especially western MA/CT. Will have to see how later model runs trend but it`s possible much if not the entire day remains dry across RI and eastern MA. Low level WAA should result in highs in the 50s across the coastal plain including the Boston to Providence corridor, with 40s farther inland where it will take longer to modify shallow cold air. SSW winds will increase as low level jet approaches the region. Model soundings suggest wind gusts up to 40 mph along the south coast by late in the day Saturday. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Highlights... * Gusty SW winds Saturday night will shift to W-NW Sunday into Monday, with some strong gusts during each day * Milder air moves across the region Tuesday, only to exit as another cold front brings colder air and gusty winds at mid week * Early outlook for Thanksgiving appears to be dry but cool Overview... Progressive mid level steering flow continues through this forecast period across the lower 48. Noting a couple of fast moving low pressure systems in the northern stream, though it appears that the steering flow pushes further N into southern Canada early next week. Rather strong winds accompany two passing systems, which could produce wind advisory level winds from Saturday night into Monday. The stronger of the two systems passes across southern Quebec Sunday, with gusty SW winds Sat night into Sunday shifting to W-NW Sunday night and Monday. As the pattern flattens out Monday night, will see another system move across central Quebec closer to Hudson Bay around mid week. Most of the mid level energy and moisture will be well N of the region, so expect dry conditions as another shot of cooler air moves in. High pressure appears to keep fair weather across the region for Thanksgiving though it will be cool with temps running 5 to 10 degrees below seasonal levels. Details... Saturday night... Will see temps rising during the night on mild SW winds. H925 temps rise to +11C to +12C during the night. Will also see gusts up to 35-40 kt possible, highest along the S coast. May get close to Wind Advisory levels, but will monitor as marginal low level lapse rates in place except along the immediate S coast. Have used a non-diurnal temp trend through the night. As cold front moves into western areas toward daybreak, could see some brief higher gusts, up to 45 kt, as winds start to shift to W. Showers move across through the night, and could see a few heavier downpours across western areas after midnight. This could also help mix some higher winds down with the precip. QPF amounts could reach up to 0.3 to 0.5 inches from central Mass and NE CT westward through the night. Lows will occur early, ranging from around 40 across the E slopes of the Berks to the lower 50s along the immediate S coast. Sunday and Monday... The cold front will push offshore by midday, but could see temps top off in the mid-upper 50s across central and eastern areas before frontal passage. Showers will move E during the day with improving conditions during the afternoon. A few showers might linger into Sunday evening across E coastal areas. Another round of gusty W-NW winds will move in Sunday and and continue into Monday. Will again have to monitor for Wind Advisory level sustained winds and/or gusts, especially across eastern areas. Best shot for strongest winds looks to occur along the coast, but could also see some of the strong winds across the higher inland terrain. Temps will drop back to the 20s away from the coast, up to 30-35 on the shoreline Sunday night, with readings only recovering to the 30s inland and 40-45 at the shore on Monday, running 5 to 10 degrees below seasonal levels. Tuesday and Wednesday... Low pressure moves E out of Ontario Tuesday, remaining across central Quebec early Wednesday. Associated cold front sweeps across the region Tue night. Most of energy and moisture will remain N of the region, so will just see a wind shift push across. After temps running up to 5 degrees above normal on Tuesday, readings will dip closer to seasonal levels Wednesday. Wednesday and Thanksgiving... Mainly dry conditions expected through the holiday as mid level storm track looks to remain N of the region. Winds shift to NW early Wed morning as a dry cold front pushes offshore, followed by large high pressure building E out of the central U.S. toward the eastern seaboard on Thanksgiving. Noting some model solution spread, though the 00Z GFS and ECMWF were pretty close in their surface high pres position. Looks like temps will run close to or a bit below seasonal levels. && .AVIATION /16Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/... Through Today...High confidence. Low end VFR SCT-BKN clouds will lift through the morning. Clouds will tend to dissipate from midday into this afternoon, but some clouds will linger along E coastal areas. Main issue continue to be gusty NW winds with speeds up to 30-35 kt, and low risk of gusts up to 40 kt across higher inland terrain and along the immediate coast. Tonight...High confidence. VFR. Dry weather along with diminishing winds. Saturday...High confidence. VFR, light winds and dry weather thru the morning. MVFR and rain begin to increase from west to east, with current timing 21z-00z. Also S-SW winds increase during the afternoon with gusts approaching 35 kt by late in the day along the south coast including Cape Cod and the Islands. KBOS Terminal... High confidence in TAF. Main issue today will be gusty NW winds up to 30 kt. KBDL Terminal... High confidence in TAF. Main issue today will be gusty NW winds up to 30 kt. Outlook /Saturday Night through Tuesday/...High confidence. Saturday Night: Mainly MVFR, with local IFR possible. Strong winds with local gusts to 40 kt. SHRA, patchy BR. Sunday: Mainly VFR, with local MVFR possible. Strong winds with gusts to 40 kt. Chance SHRA. Sunday Night through Monday: VFR. Windy with gusts to 35 kt. Monday Night: VFR. Windy with local gusts to 30 kt. Tuesday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/...High forecast confidence. Today... Replaced the Gale Warning for Cape Cod Bay a little earlier than it would have expired with a Small Craft Advisory. That will be the trend for today with the other coastal waters. extended the Gale Warning a couple of hours for the outer coastal waters south and east of the Cape and islands, where latest buoys indicate gale force gusts continuing. Previous discussion... NW gales across open waters this morning, lingering to gale force across the eastern waters this afternoon. Dry weather and good vsby prevail. Tonight... Light winds as high pressure crest over the New England waters. Saturday... light winds to start the day but increasing SSW winds during the afternoon and possibly reaching Gales by sunset across the RI and southern MA waters. Showers may also arrive late in the day. Outlook /Saturday Night through Tuesday/...Moderate confidence. Saturday Night: Low risk for gale force winds with gusts up to 40 kt. Areas of rough seas. Rain showers likely, patchy fog. Sunday and Sunday night: Moderate risk for gale force winds with gusts up to 40-45 kt. Rough seas up to 12-15 ft. Rain showers likely Sunday. Monday: Moderate risk for gale force winds with gusts up to 40 kt. Rough seas up to 11 ft. Monday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Watch from Saturday afternoon through Sunday afternoon for ANZ232>237-255-256. Small Craft Advisory until 1 AM EST Saturday for ANZ231>235- 237-256. Small Craft Advisory until 7 PM EST this evening for ANZ230- 236. Gale Warning until 1 PM EST this afternoon for ANZ250-251-254. Small Craft Advisory until 5 AM EST Saturday for ANZ255. && $$ SYNOPSIS...Nocera/EVT NEAR TERM...Belk/Nocera/EVT SHORT TERM...Nocera LONG TERM...EVT AVIATION...Nocera/EVT MARINE...Belk/Nocera/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.