Area Forecast Discussion
Issued by NWS Boston, MA

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945 FXUS61 KBOX 281758 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 158 PM EDT SUN AUG 28 2016 .SYNOPSIS... High pressure centered over the Canadian Maritimes brings dry weather through today. A cold front moves south into New England tonight and then exits later Monday, which may be accompanied by a spot shower or thunderstorm. Weak high pressure brings dry and less humid conditions Tuesday. Warm and humid weather returns Wed ahead of another cold front, which will bring the chance for showers and thunderstorms Wednesday into early Thursday. Large Canadian high pressure will bring dry, fall like weather late this week into the weekend, with mild days and cool nights. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 2 PM Update... Fabulous late summer weather at 2 pm with mostly sunny conditions and temps in the upper 70s and lower 80s...mid 80s away from the shoreline. Humidity somewhat comfortable with dew pts 55 to 60. Previous forecast captures these details nicely so no major changes with this update. Earlier discussion below. Previous Discussion... Deep layer ridge over the Northeast this morning yielding plenty of subsidence and resulting in mostly sunny conditions. SPC mesoanalysis indicates higher dew pt air at 925 mb and 850 mb remain well to the west of New England. Thus any convection from upstream short wave energy will remain west of New England. Hence dry forecast remains intact. As for temps...weak pres gradient over the area with 1027 mb surface high centered over the maritimes will promote cooling seabreezes for the shoreline. Previous forecast captures this nicely...thus no major changes with this forecast update. Earlier discussion below. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... A mid level shortwave from the Plains moves east to Quebec tonight, then moves south across New England Monday. The best dynamics, in the form of a 100+ knot upper level jet, still looks like it will stay mainly to our north. That means most of the forcing for rainfall will be from a shortwave, a weak cold front, and whatever convective instability can be generated. Given that most of this will occur at night into the morning hours, not expecting strong thunderstorms. These attributes should also keep areal coverage of any storms isolated or widely scattered. Thus not a washout expected. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * Expect mainly warm and dry conditions on Tuesday, with more humidity returning on Wednesday * A cold front brings the chance for showers/thunderstorms Wednesday afternoon into early Thursday * Fall like conditions move in for Friday and Saturday with mild days and cool nights Overview and model preferences... Models and ensembles remain in good agreement in the overall mid level steering pattern across North America with an amplified northern stream extending across central and southern Canada early this week. However, noting changes by mid week, as H5 heights fall as long wave trough digs across New England in response to large H5 ridge building from the Plains states northward into Nunavut and the Northwest Territories of N central Canada toward the Arctic Circle. The high amplitude pattern does remain progressive, so will see the large ridge building slowly but steadily eastward through the remainder of the week. Will see another H5 short wave in the flow approach during late Wednesday night/Thursday in the NW flow. Will see some showers/ thunderstorms move across with rather weak surface front. Not a lot of support with this, but a pretty sharp temperature difference behind the front. Will see a batch of cooler air work in late this week as the cold front pushes offshore, feeling more fall like by the upcoming holiday weekend. Have rather good confidence for the overall timing of this forecast package, though somewhat lower confidence from Wednesday night onward on specific details. Used a blend of available guidance through Wednesday, then leaned more toward the model ensemble guidance for the latter portion of the forecast. Details... Monday night...The cold front will push offshore without much fanfare. Cooler air works in across the region, with H85 temps falling to +10C to +12C by daybreak. With mainly clear skies and light N-NW winds, expect temps to fall back to near seasonal levels. Readings will bottom out in the mid-upper 50s across inland valley locations to the mid-upper 660s along the immediate coast. Tuesday...High pressure ridge builds across, bringing dry conditions and low humidities. With a light pressure gradient across the region thanks to the passing high, sea breezes will bring slightly cooler temperatures along the shoreline. Wednesday...Another cold front begins to approach N and W Mass Wed afternoon, then will steadily move SE. Will see warm and more humid conditions ahead of this system as SW winds pick up. Noting the PWATs do increase by Wednesday evening to 1.6 inches, so could see some brief heavy downpours with any thunderstorms across central and southern areas toward evening. Wednesday night-Thursday...Scattered showers and a few thunderstorms may linger across N CT/RI into SE Mass early Wednesday night as the cold front passes. The front may even slow down near the south coast by Thursday morning, so some showers may linger there for a part of the day. Will still see mild temperatures as the cooler air does not work into the region until later in the day, but dewpts will be falling so it will be mild but more comfortable as the day progresses on Thursday. Friday and Saturday...Large high pressure will build SE out of north central Canada across the Great Lakes, bringing cool temps especially Friday morning. H85 temps will drop to +5C to +8C by 12Z Friday, which will linger through the day. Expect highs on Friday to run up to 5 degrees below seasonal normals. May see some overnight lows early Saturday morning into the upper 40s well inland, but will recover with mainly clear skies and temperatures reaching close to or a bit above normal for early September. && .AVIATION /18Z SUNDAY THROUGH FRIDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/...High Confidence. 2 PM update ... Thru 03z ... high confidence for VFR...dry weather and mainly light southeast winds. After 03z ... VFR but isolated shower or thunderstorm with highest probs across northwest MA...then shifting into eastern MA toward sunrise. High forecast confidence. Monday ... VFR with low risk of a spot shower or T-storm eastern MA in the morning then shifting to south coast midday...then offshore by mid afternoon. West-southwest winds in the morning becoming NW 10-20 kt by midday. High confidence. Mon night ... light NNW winds becoming variable late. VFR and dry weather too. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Tuesday through Thursday/... Tuesday...High confidence. VFR. Expect dry conditions. Light W-SW winds inland. Sea breezes along both coasts likely. Patchy fog late Tuesday night with local MVFR-IFR VSBYS. Wednesday...Moderate confidence. Mainly VFR. May see local MVFR conditions in scattered SHRA/TSRA across N central and W Mass during the afternoon. Wednesday night-Thursday...Moderate confidence. Mainly VFR. Local MVFR-IFR CIGS/VSBYS in scattered SHRA/TSRA as cold front crosses the region Wednesday night. The front may slow down along the S coast Thursday morning, so a few showers may linger until around midday Thursday before improving. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/...High confidence. Seabreezes will return late this morning and continue through this afternoon. Seas trend slowly higher into Monday in response to southeast swell from distant Hurricane Gaston. A widely scattered shower or thunderstorm possible late tonight into Monday as a cold front crosses the waters. Outlook /Monday Night through Thursday/... Monday night...Moderate to high confidence. W-SW winds early shift to NW as cold front pushes offshore. May see a few leftover showers Monday evening across the southern waters with briefly reduced visibilities. S-SE swells will increase across the outer waters from distant Hurricane Gaston. Tuesday...High confidence. Light N-NE winds shift to SE during the day. May see briefly reduced visibilities late Tuesday night in patchy fog on the near shore waters. S-SE swells from Hurricane Gaston continue on the outer waters. Wednesday...Moderate to high confidence. SW winds increase, with gusts up to 20 kt mainly across the eastern waters where seas will increase to around 5 ft. Local visibility restrictions in scattered showers/thunderstorms may approach the eastern waters Wednesday afternoon. Wednesday night-Thursday...Moderate confidence. A cold front crosses the waters with scattered showers/thunderstorms Wednesday night into early Thursday morning. A few showers may linger through midday across the southern waters. Winds shift from SW to W-NW by Thursday morning, then N-NE on the eastern waters Thursday afternoon. Seas may occasional reach 5 ft on the eastern outer waters Thu into Thu night. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/EVT NEAR TERM...Nocera SHORT TERM...Belk LONG TERM...EVT AVIATION...Nocera/EVT MARINE...Belk/EVT

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