Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201136 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 636 AM EST Sat Jan 20 2018 .SYNOPSIS... Mild and dry weather expected this weekend, along with gusty west to southwest winds today. 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/... 635 AM update... Some high clouds moving across SNE this morning and this will continue through the day as northern stream shortwave passes to the north. Still expect pt-mosunny skies through high clouds. Main issue today will be the gusty winds near the coast which is already reflected in current forecast. Previous discussion... With increasing pressure gradient moving across the region, as well as strong low level jet (on order of 45-55 mph from H95 to H9) moves across, W-SW winds will increase. Gusts are forecast to reach 30 to as high as 40 mph, with highest gusts along the S coast, Cape Cod and the islands. Will need to monitor portions of the Cape as well as Martha`s Vineyard and Nantucket to see if Wind Advisories may be needed for a time. It will be a mild day especially across central and eastern areas as temps look to reach around 50 degrees, though will be a bit cooler along the S coast with the SW winds off the colder ocean waters. Across N central and W Mass into N central CT, readings may hold in the lower-mid 40s especially across the higher terrain. Expect a dry cold front to approach N Mass during the afternoon, which will push southward toward sunset. Winds will become mainly W and start to diminish as the front passes. && .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 /12Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday/... Today...Moderate confidence. Mainly VFR conditions, though may see low end VFR CIGS develop across E slopes of the Berkshires by midday through the afternoon. Expect W-SW winds to gust up to 25-30 kt across the higher inland terrain, ranging up to around 35 kt along the S coast, Cape Cod and the islands with low risk of 40 kt gusts during the afternoon. Threat of LLWS through 16Z-18Z as a 45-55 kt SW jet at and just above 2Kft AGL moves across, with best chance from KPVD-KPYM southward. Tonight...Moderate confidence. VFR. May see patchy MVFR CIGS across the E slopes of the Berkshires off and on through the night. W winds will diminish, but may see leftover gusts up to 25-30 kt along the S coast early. Sunday...High confidence. VFR. W-NW winds around 10 kt or less as pressure gradient relaxes. KBOS Terminal...High confidence in TAF. VFR conditions expected. W-SW winds gusting up to 20-25 kt, highest around midday into mid afternoon. KBDL Terminal...High confidence in TAF. Outlook /Sunday Night through Wednesday/... Sunday Night: VFR. 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. Have continued Gale Warnings across most of the waters as W-SW winds will gust up to 25-35 kt today, 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. As a cold front approaches, winds will shift to W 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...KJC/EVT NEAR TERM...KJC/EVT SHORT TERM...EVT LONG TERM...KJC AVIATION...KJC/EVT MARINE...KJC/EVT HYDROLOGY... is the U.S. government's official web portal to all federal, state and local government web resources and services.