Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 221404 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1004 AM EDT SUN MAY 22 2016 .SYNOPSIS... Coastal low pressure brings wet weather today as it passes well offshore of Nantucket. The low continues on to Nova Scotia tonight. We get a break in the wet weather tonight and Monday. A second low pressure then moves up the coast and brings more scattered showers Monday night and Tuesday. A significant warmup will occur Wednesday...continuing into next weekend. Scattered showers or thunderstorms are possible from Thursday into the weekend, especially in western sections. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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10 am update... Cool and unsettled giving way to a mix of sun and clouds along with mild conditions. Coastal low E lifts NE today behind which there is some weak ascent associated with the cold conveyor belt from the E sweeping W towards upstream energy diving S out of SE Ontario, but also dry sinking air out of the N especially around h6-8 where a majority of present clouds reside. These motions are apparent within the latest radar returns if you look closely. Seeing some decent convergence of airstreams across Central New England, cold conveyor belt from the E converging against the dry conveyor belt from the N. So can not rule out a spot shower. Confidence across the high terrain with some orographic influences plus forcing along a weak cold front dropping S across Upstate NY and PA with the aforementioned upstream energy and broadscale troughing, as well as across E/SE coastal New England in reference to the airstreams noted earlier. So gradually clearing conditions across the interior while warming into the 70s. Whereas chilly NE flow around the coastal low will yield cool and clammy conditions for the E/SE coast. It is in those cool and clammy conditions that drizzle and light rain showers are forecast. There is a high risk of rip currents today into this evening along the eastern portions of Cape Cod and Nantucket, as well as along the south coast, from Bristol County, MA to Westerly, RI.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/...
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Upper closed low settles in to place centered over Virginia with the closed circulation extending up the coast to New England. This circulation along with plenty of moisture between 850 mb and 700 mb should maintain at least partly cloudy skies Sunday night and Monday. Dew points in the 40s should keep surface temps in the mid 40s to lower 50s. The sunshine that does occur on Monday should bring surface temps into the upper 60s and lower to mid 70s inland. A developing northeast wind will move ashore on the Cape and Islands and East Coastal Massachusetts and keep max surface temps in the upper 50s and 60s there. Upper jet moving around the closed low will move the associated surface low north on Monday. The favorable left exit region of this jet, which will support lift and shower development, will also move north. Current model information holds this feature south of New England through much of Monday. It may come close enough to bring a few showers to the South Coast late in the day. Most if not all of the showers should wait until Monday night.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * Good chance of showers Tuesday * Significantly warmer Wednesday into next weekend * Scattered showers and thunderstorms Thursday into the weekend, especially in western sections. Overview and Model Preferences... Upper level low pressure passes northeast from the Mid-Atlantic coast, reaching the Gulf of Maine Tuesday night. By Thursday and Friday, and continuing into next weekend, a strong upper level ridge develops over the Mid- Atlantic states...extending northward into western New England. In general, models are in good agreement at the upper level features but differ somewhat on timing and location of possible convection later in the week. All agree on a major warmup to summertime levels. There will also be increasing moisture. A warm frontal boundary could provide the focus for scattered thunderstorms Thursday as it moves northward. Scattered showers or thunderstorms will be possible during the afternoons and evenings into the weekend. Details... Monday night into Tuesday... Core of the upper level cold pool moves over southern New England Mon night into Tue...with -18C at 500 mb...which is cold but not that extreme. Models are now in better agreement on the track of surface low pressure, which moves between outer Cape Cod and the benchmark of 40N 70W on Tue. The ECMWF, which had it moving into RI, is thus a bit less unstable than it was. We will need to keep an eye on the possibility of some nocturnal thunderstorm activity for southeastern MA and RI Mon night. All models show a rapid influx of unstable air into southeastern sections between midnight and daybreak Tue. Total Totals Indices reach 55 and there is an indication of very unstable lapse rates of 7C from 700-500 mb. 0-6 km bulk shear values increase to 45-55 kts from the south-southeast at that time, too. However, with cool northeast surface flow, there is no Convective Available Potential Energy (CAPE). This is not the usual situation to expect a chance of thunderstorms, but we have veering of wind with height (WAA) and increasing speeds with height... so, could see some organized, but scattered and elevated thunderstorms, especially RI and southeast MA late Mon night. Scattered showers or an isolated thunderstorm will gradually move away by Tue evening. Highs Tue will hold in the 65 to 70 range due to cloud cover and scattered showers. Wednesday... Brief ridge of high pressure to our south takes over, leading to downslope air flow, drier conditions, and more summer-like temperatures with highs in the lower 80s away from the coast. There could be sea breezes, but it appears the synoptic flow could be just strong enough to prevent lower temperatures along parts of the MA east coast. Cape Cod and the islands, as well as Cape Ann, however, will likely hold in the upper 60s to lower 70s. Thursday through Saturday... On Thursday, 925 temps warm to +21C, so am forecasting mid 80s in the CT valley and 80-85 elsewhere, cooler at the coast. A warm front extending eastward from low pressure in western NY may provide the focus for scattered showers and thunderstorms Thu afternoon and evening. The GFS shows an axis of 36 K Index, indicating a lot of moisture and instability, extending eastward along the MA/CT/RI border by 00z. ECMWF, however, keeps it all to our west. So will go with chance PoPs for now. Warm weather with highs in the 80s are expected Friday and Saturday with a front mainly north of the area. Diurnally-driven showers and thunderstorms are possible both days, especially across the western half of southern New England. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/... Today and Tonight...High Confidence. Overall VFR but MVFR lingering over E/SE coastal terminals along with the threat of -SHRA. NE winds with gusts up to 30 kts again mainly for E/SE coastal terminals into this afternoon diminishing into evening and overnight hours. Monday...Moderate Confidence. Low-end VFR cigs with MVFR across E/SE coastal terminals. Low risk of IFR. -SHRA developing through the course of the day increasing in areal coverage late. NE flow prevailing with gusts up to 20 kts especially over the E/SE coast. KBOS TAF...There is a low risk of MVFR across the terminal. Majority of the TAF period will be low-end VFR with NE winds. Gusts limited up to 15 kts. KBDL TAF...Potential SCT-BKN cigs developing later today. Otherwise VFR with N winds with gusts limited to 15 kts. Outlook /Monday night through Thursday/... Monday night into Tuesday...Moderate Confidence. Although not a complete washout, scattered showers will continue across the area with northeasterly flow. An isolated thunderstorm is also possible. This also suggests low clouds. Therefore, periods of MVFR/IFR are likely, but it`s possible that occasional VFR will occur, especially across the interior. Wednesday...High Confidence. Mainly VFR. Thursday...Moderate Confidence. Mainly VFR. Scattered MVFR in scattered showers and thunderstorms, mainly west of KLWM-KORH-KIJD.
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&& .MARINE...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 10 am update...no major changes to the forecast. Today... Moderate confidence. Low pressure passes about 125 miles southeast of Nantucket early afternoon. Spot showers continuing but little obstruction to visibility. Winds increasing from the NE with gusts 25 to 30 knots. Seas build 5 to 9 feet on the outer waters and the RI waters. Small Craft advisory continues. Tonight... Moderate confidence. Low pressure moves off across Nova Scotia. This will turn winds from the north with diminishing speeds. But seas will linger at 5 to 9 feet, mainly across the outer waters. Small Craft advisory continues on most waters due to seas. Monday... High confidence. North winds diminish in the morning. Lingering 5 to 7 foot seas on the Eastern Outer Waters. Low pressure moves up from the south during the late afternoon and spreads showers across the Southern waters with briefly low vsbys. This will also turn winds from the northeast, but speeds will remain at or below 20 knots. Small Craft Advisory will continue to be needed on the Eastern Outer Waters. Outlook /Monday Night through Thursday/... Monday night and Tuesday...Moderate Confidence. Winds still remain below 25 kt, but a second approaching low pressure will allow for building southerly swell. Seas may reach 7 to 8 feet south of Nantucket. Small craft advisories may need to continue for some waters. Wednesday into Thursday...High Confidence. High pressure briefly builds over the waters. Mainly quiet boating weather is expected with winds and seas below Small Craft Advisory levels.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Rip Current Risk through this evening for MAZ020-022-024. RI...High Rip Current Risk through this evening for RIZ006>008. MARINE...Small Craft Advisory until 11 PM EDT this evening for ANZ231>234. Small Craft Advisory until 5 AM EDT Monday for ANZ235-237. Small Craft Advisory until 6 PM EDT Monday for ANZ250-254>256. Small Craft Advisory until 6 PM EDT Monday for ANZ251. && $$ SYNOPSIS...WTB/GAF NEAR TERM...WTB/Sipprell/GAF SHORT TERM...WTB LONG TERM...GAF AVIATION...WTB/Sipprell/GAF MARINE...WTB/GAF

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