Area Forecast Discussion
Issued by NWS Boston, MA

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772 FXUS61 KBOX 142135 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 435 PM EST Sat Jan 14 2017 .SYNOPSIS... High pressure moves E of the region today with a weak low pres sliding well S of the coast overnight. Some light snowfall is possible mainly across Connecticut, Rhode Island and Southeast Massachusetts late today and tonight. High pressure maintains dry and seasonable conditions Sunday and Monday. Low pressure from the Plains approaches Southern New England with rain and mild air for Tuesday and Wednesday. The low then redevelops to our east and moves off Wednesday night. High pressure then builds in with dry and continued mild weather for the end of the week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Clouds continue to thicken especially across central and southern areas at 20Z, while noting breaks in the high clouds over NE and north central Mass as seen on latest visible satellite imagery. Strong high pressure, with readings up to 1040 hPa this morning, will continue to shift E through this evening. Noting overrunning precip working across S NY into Long Island and SW CT on latest NE regional 88D radar mosaic. Even with wide temp/dewpt spreads, have noted a few spots with -SN, including the three NYC airports, KHPN and KISP at 20Z. Visibilities down below 2 SM at the NYC airports, but should not last long as precip moves steadily E. Winds have shifted to S-SE though remain light across the region. They may back to a SE direction along the S coast, which may allow enough low level moisture, even with the low dewpts, to bring some spotty light snow along the S coast of MA/RI overnight. NAM 4 KM, RAP and GFS BUFKIT soundings are signaling light snow reaching into KEWB, KCHH and KHYA overnight, and even for a few hours as far N as KPVD. Think it will be tough to get it into KPVD at this point, but still a shot along the coast. Models are suggesting that dewpts do rise as the northern edge of the precip pushes across, but they have had a warm bias all day today, so not confident they will rise as quickly as the models are suggesting. Have CHC POPs hugging along the S coast through around 06Z, then should exit quickly as another high starts to push E out of the Great Lakes. Strong mid and upper level jet across the region with W-NW winds up to 135 kt at H3 on 12Z KCHH sounding and 140 kt at H25 on KALB sounding. Short range models all show this sitting across the region overnight, then pushing E after 06Z Sun. Skies should start to clear across N central and W Mass after 10 PM or so, then will quickly shift eastward overnight pushing toward the S coast toward daybreak. Winds shift to W-NW with the approaching high. Expect temps to bottom out in the teens across most areas, except in the 20s along the immediate coast. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday... While high pressure moves E across W NY state early Sunday, a second high will shift E out of central Quebec. This will bring a reinforcing shot of cold air across the region during the morning. Noting a 30-40 kt jet shifting SE from H85 to H9 as the front approaches. Will see good low level mixing push into the region from H92 and below, especially across the waters by around midday and through the afternoon. Expect mainly clear skies across most of the region, but some clouds will linger across the E slopes of the Berkshires. H92 temps drop to -5C to -9C by 15Z Sun then level off at -5C to -7C during the afternoon. Should see high temps from the mid 20s to around 30 across the higher inland terrain to the upper 30s along the S coast. Sunday night... Large high pressure center will slowly cross NY state/PA, with N-NW winds diminishing during the night. Expect mainly clear skies through the night and, as the winds drop off, will see temps fall as well with good radiational cooling setting up. Expect overnight lows ranging from 5 to 15 across most areas, ranging to the upper teens and 20s along the immediate coast and urban centers. && .LONG TERM /MONDAY THROUGH SATURDAY/... Big Picture... Hudson Bay upper low retreats north, leaving a large-scale zonal flow for much of the long term. Toward next weekend the large scale a developing Pacific Coast trough and West Atlantic Ridge. In the shortwave scale, Baja California upper low ejects through the Southern Plains Monday and Great Lakes Tuesday, then New England Wednesday. East Coast ridge then builds late week. Contour heights are mostly forecast to be above the climatological average. GFS does show heights briefly near normal Wednesday as the upper trough moves past, but the ECMWF and GGEM are much warmer. Overall this looks like a dry mild week, punctuated by a period of rain Tuesday-Wednesday. Model mass fields are similar through Wednesday morning, then diverge in handling the midweek weather system. They then show a general agreement on high pressure arriving for Friday and Saturday. Confidence for the long term is moderate. Details... Monday... High pressure settled offshore, bringing a light west to southwest flow. The mixed layer reaches to about 950 mb, where temps support max sfc temps of 35 to 40. Some increase in cirrus at night, especially across CT and RI, but otherwise fair skies and light winds. This will allow radiational cooling for a portion of the night. Dew points 15 to 30 should allow min temps mainly 20-30. Tuesday-Wednesday... Models are trending slower with the onset of clouds and precipitation. The lower airmass remains dry through midday while mid and high clouds are on the increase. Low level ageostropic flow turns from the north but remains 20 knots or less. Meanwhile temps will have time to climb above freezing in most places. If cold air does linger, it would be most likely in some of the East Slope communities of Northwest MA. There also remains a chance that the combination of slightly stronger drainage flow and evening evaporative cooling could bring a period of freezing rain in Northwest MA. This will need to be monitored. Aside from that potential icing scenario, temperature profiles suggest rain for our area from onset to finish. Models are showing a coastal redevelopment of the system on Wednesday, but disagree on the location. The GFS says Gulf of Maine while the ECMWF says Long Island. The GGEM tries to do a little of both. Still plenty of time for these details to sort out. Thursday through Saturday... The ECMWF shows a second shortwave sweeping down from Canada Thursday while the GFS shows, at best, a very shallow version of one. This may be good for snow showers in the hills, but moisture profiles are sufficiently dry to maintain a dry forecast. High pressure then builds in for Friday and Saturday. Temps in the projected mixed layer support max sfc temps in the 40s. Dew points are projected in the upper 20s and 30s, supporting lows in the 30s. && .AVIATION /22Z SATURDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday night/... Through 00Z...High confidence. VFR. BKN-OVC AOA 10Kft. BKN-OVC AOA 10Kft. Light S-SW winds. May see some low end VFR clouds move into S RI coast by around 00Z. Tonight...Moderate confidence. VFR conditions continue across most areas. May see a period of MVFR CIGS/VSBYS in any -SN that develops along the S coast of RI/S coastal Mass from around 00Z through 06Z-08Z from W-E. A few -SHSN may reach as far N as KIJD-KPVD-KPYM for a short time late tonight. Any MVFR conditions should improve during the predawn hours Sunday. Light SW winds shift to NW as the precipitation ends. Winds may gust up to 20 kt on outer Cape Cod as winds shift after midnight. Sun...High confidence. VFR. NW winds gusting to 20-25 kt along the immediate E coast, Cape Cod and the islands through early afternoon, then diminish. Sunday night...High confidence. VFR. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF overall. Low risk for spotty light snow this evening, but should remain mainly VFR. Outlook /Monday through Thursday/... Monday...High confidence. VFR. Tuesday-Wednesday...Moderate confidence. VFR Tuesday morning, lowering to MVFR cigs/vsbys in rain Tuesday afternoon/evening, then IFR in rain and fog Tuesday night and Wednesday. Conditions may improve Wednesday afternoon. Variable winds Tuesday becoming S-SE Tuesday night, S-SW Wednesday, and West by Wednesday afternoon. Thursday...Moderate confidence...VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/... Through 00Z...High confidence. Winds and seas below small craft criteria. Tonight...High confidence. Light SW winds increase overnight. May see gusts to 20 kt on the eastern open waters after midnight as they shift to NW. Seas 4 ft or less. Some brief visibility restrictions across the southern waters to SE of Cape Cod in light rain and/or snow. Sunday...Moderate to high confidence. NW winds gusting to 25 kt on the eastern open waters and Mass/Ipswich Bays. Seas may reach 5 ft there as well. Small craft issued. Winds should diminish on the near shore waters around midday, but will linger on the outer waters through the day. Sunday night...High confidence. Any leftover NW wind gusts to 25 kt will diminish Sunday evening on the eastern outer waters. Seas should also subside below 5 ft. Outlook /Monday through Thursday/...Moderate confidence. Monday-Tuesday... Winds less than 20 knots and seas less than 5 feet. Tuesday night-Wednesday... Southeast winds reach 25 knots on the outer waters and possibly RI Sound, with seas building to 5-7 feet. Best chance is on the southern outer waters. Small Craft Advisory may be needed on these waters. Visibility will be reduced in periods of rain Tuesday night, with rain tapering off as winds shift from the West Wednesday afternoon. Thursday... Northwest winds will gust to 25 knots on some of the waters. Seas of 5-7 feet will slowly diminish during the afternoon. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 6 AM to 9 PM EST Sunday for ANZ250- 254. Small Craft Advisory from 6 AM to 1 PM EST Sunday for ANZ251. && $$ SYNOPSIS...WTB/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...WTB AVIATION...WTB/EVT MARINE...WTB/EVT

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