Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201728 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1228 PM EST Sat Jan 20 2018 .SYNOPSIS... Mild and dry weather expected this weekend, along with gusty west to southwest winds this afternoon. A storm system will bring the potential for heavy rain and strong coastal winds on Tuesday, but this will be preceded by a risk of some wintry mix/ice across the interior late Monday into Tue morning. Blustery, dry and colder weather follows Wednesday through Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The weather is still going on, but not much happening at this time. A zone of high clouds is sweeping across. Webcams suggest some thicker zones where the clouds may be dimming the sun. Some signs of a weak cold front in northwest Massachusetts, but it is quite subtle. Surface obs show gusty west-southwest winds over RI and Eastern Mass. Morning upper air observations show roughly 30 knots at 925 mb, although Gray Maine is reporting 40 knots. Surface gusts are reported at 20 to 30 knots. Temperatures at the top of the expected mixed layer are equiv to -5C or -6C at 850 mb. This would support max temps in the mid 40s to lower 50s. So expect the day to sunshine with varying amounts of dimming...call it partly sunny. Above normal afternoon temperatures for mid January. Winds will be gusty to about 30-35 mph. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Tonight... The cold front should clear the S coast overnight as it weakens. Wind will become W-NW but should be on the light side though may see some gusty conditions, up to around 20 kt or so, on portions of Cape Cod through the evening. Pressure gradient does relax between high pressure off the SE coast and another high building SE out of central Canada. Noting dewpoints will remain relatively high as the colder air works in. May see some patchy fog develop after midnight across central and western areas, along with clouds that may linger from time to time across N central and W Mass. Expect temps to bottom out in the mid 20s to lower 30s across most areas, except from 30-35 along the immediate coast. Sunday... Clouds early Sunday should push further inland, so should see mostly sunny skies during the day. Still somewhat milder air will remain across the region as winds become light and variable. Expect highs to range from 5 to 10 degrees above seasonal normals. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Highlights... * Risk of light wintry mix/ice interior MA late Mon into Tue AM * A period of heavy rain and strong coastal winds likely Tue * Dry and colder Wed-Fri Sunday night into Monday night... Subtle cold front will drop south across SNE late Sun night into Mon as strong high pres builds across SE Canada. Weak overrunning to the north of this stalled boundary and a gradual moistening of the column will result in light precip developing across SNE, mainly Mon afternoon into Mon night. Pronounced cold air damming signature noted with high pres over the Maritimes and sfc ridging nosing down across SNE will set the stage for some wintry precip in the interior. Thermal profiles initially support mixed precip with some light snow/sleet/freezing rain into the evening, with risk transitioning to areas of freezing rain during Mon night interior northern MA as warming aloft becomes more pronounced while low level cold air hangs tough. Some uncertainty with how long low cold air near the surface hangs on but some of the guidance has it lingering into Tue morning for interior northern MA. Increasing risk for some travel impacts. Tuesday... Other than a risk of some freezing rain lingering across interior northern MA in the morning, ptype will be all rain. Period of heavy rain appears likely on Tue moving west to east across SNE as strong low level jet develops ahead of the cold front. PWAT anomalies +2SD with low level wind anomalies up to 2-3SD which is a good signal for heavy rainfall. In addition, marginal elevated instability develops supporting a risk of some convection and elevated thunder. Deterministic GFS/ECMWF/GGEM all show potential for QPF of 0.75 to 1.5 inches and ensemble guidance supports this with moderate to high probs of 1+ inches. This system is rather progressive which should prevent rainfall from exceeding these amounts. Other concern for Tue is potential for strong winds accompanying the 65-70 kt low level jet. Low level lapse rates are forecast to be near moist adiabatic which would allow for decent mixing, especially where temps get into the 50s across RI and eastern MA. Potential for wind advisory gusts, especially in any heavier showers/convective activity. Not expecting much impact to river ice as there is only a brief window of higher temps/dewpoints on Tue followed by colder conditions. Wednesday through Friday... Turning colder and blustery behind the departing storm in NW flow pattern. Temps near normal Wed trending below normal Thu/Fri. Coldest day expected to be Thu as GEFS and EPS showing ensemble mean 850 mb temps dropping to -12 to -14C across SNE. Temps on Thu likely remaining below freezing across much of SNE with 20s interior. Mainly dry weather expected during this period, although a brief flurry/snow shower can`t be ruled out Wed/Thu over higher terrain as a few shortwaves move through. && .AVIATION /18Z 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/... This afternoon...High confidence. VFR. WSW winds will gust around 30-35 knots especially on Cape Cod and Islands. Tonight...High confidence. VFR. May have patchy MVFR cigs along the eastern slopes of the Berkshires in NW Massachusetts. Diminishing WNW winds. Sunday...High confidence. VFR. W-NW winds around 10 kt or less as pressure gradient relaxes. Sunday night... Moderate confidence. VFR. Increasing sky cover late at night. KBOS Terminal...High confidence in TAF. WSW winds may gust 30-35 knots at times this afternoon, diminish this evening. KBDL Terminal...High confidence in TAF. Outlook /Monday through Wednesday/... Monday: MVFR/IFR conditions possible. Chance RA, PL, SN. Slight chance FZRA. Monday Night: Mainly MVFR, with areas IFR possible. RA likely, FZRA likely interior northern MA. Tuesday: Mainly MVFR, with local IFR possible. Windy with gusts to 30 kt. RA. Pockets of FZRA possible early interior northern MA. Tuesday Night: VFR. Windy with local gusts to 30 kt. Wednesday: VFR. Windy with areas gusts to 30 kt. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday/...High confidence. Gale Warnings continue across most of the waters as W-SW winds will gust up to 35 kt this afternoon, highest across the southern open waters. Small Craft Advisories have also been posted across some of the sheltered near shore waters. Seas will build up to 6-9 ft, highest across the southern outer waters. A weak cold front moves across the waters this evening. Winds will then shift from the west and the pressure gradient will start to relax. Winds should diminish below gales this evening, but small crafts will likely continue through at least tonight on the open waters. Seas at or above 5 ft will linger into Sunday morning, then should subside. Outlook /Sunday Night through Wednesday/... Sunday Night: Winds less than 25 kt. Monday: Winds less than 25 kt. Slight chance of rain. Monday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain. Tuesday: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 12 ft. Rain. Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Wednesday: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 11 ft. && .HYDROLOGY... A Flood Warning remains in effect for the Connecticut River at Middle Haddam, where ice jams are causing river fluctuations. For details on specific area rivers, including observed and forecast river stages, please visit the Advanced Hydrologic Prediction Service (AHPS) graphs on our website. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Warning until 4 PM EST this afternoon for ANZ232>235-237. Small Craft Advisory until 4 PM EST this afternoon for ANZ230. Small Craft Advisory until 10 PM EST this evening for ANZ231- 251. Small Craft Advisory until 6 PM EST this evening for ANZ236. Gale Warning until 2 PM EST this afternoon for ANZ250. Gale Warning until 6 PM EST this evening for ANZ254-255. Gale Warning until 5 PM EST this afternoon for ANZ256. && $$ SYNOPSIS...WTB/KJC/EVT NEAR TERM...WTB/KJC/EVT SHORT TERM...EVT LONG TERM...KJC AVIATION...WTB/KJC/EVT MARINE...KJC/EVT HYDROLOGY...

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