Area Forecast Discussion
Issued by NWS Boston, MA

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949 FXUS61 KBOX 201945 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 245 PM EST Sat Jan 20 2018 .SYNOPSIS... A couple of weak cold fronts in the neighborhood bring a few clouds, but otherwise fair and mild weather tonight and Sunday. 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 /THROUGH TONIGHT/... The remains of a weak cold front were moving through this afternoon and evening. But the air was so dry that all we saw were an area of clouds above 15K feet. Mixing did bring gusty winds, some reaching 30-40 knots, but these will be diminishing this evening. High pressure builds in with dry weather. Fair skies, light wind, dew points in the 20s... expect min temps in the mid 20s to low 30s. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... High pressure in place Sunday with fair skies and light wind. Moisture fields do show some increasing mid and high level moisture, so expect some increasing clouds mostly in the afternoon/evening. With mixing to 950 mb, expect max temps in the mid to upper 40s, a few spots around 50. The clouds increase Sunday night. A cold front in Northern New England dips south and may slip through Southern New England. But with the upper flow west-east we do not expect a lot of push to it, and potential that it stalls either over or near us. The net change in the airmass is nil, so min temps Sunday night should be similar to tonight. Low level southerly winds reach only to Western NY/PA by 12Z Monday...still west winds over us at that time...which means little lift to be generated Sunday night. So the probability of precip should be low. If the precipitation were to move in faster, low level temperatures would support a mix with sleet and freezing rain. But that scenario looks unlikely at this time. Our forecast shows slight chance pops in Western MA/CT by 12Z Monday, and that may be overplaying the liklihood. && .LONG TERM /MONDAY THROUGH SATURDAY/... 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 /20Z 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/... Tonight...High confidence. VFR. Diminishing west wind this evening. 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. KBDL Terminal...High confidence in TAF. Outlook /Monday through Thursday/... 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 Night/...High confidence. Tonight... Diminishing wind this evening and overnight as high pressure builds over the waters. Expect winds below gale this evening and dropping below Small Craft Advisory levels tonight. Seas also subsiding tonight with the southern outer waters the last to drop below 5 feet late tonight. We are dropping gales with this forecast, and holding on to SCA for a few hours tonight. Sunday and Sunday night... High pressure over the waters should provide fair weather with light winds and seas below 5 feet. Clouds will increase overnight, but support for any precipitation will remain well to our west during the night. Outlook /Monday through Thursday/... 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- 250. 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 6 PM EST this evening for ANZ254-255. Gale Warning until 5 PM EST this afternoon for ANZ256. && $$ SYNOPSIS...WTB/KJC NEAR TERM...WTB SHORT TERM...WTB LONG TERM...KJC AVIATION...WTB/KJC MARINE...WTB/KJC HYDROLOGY...

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