Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 221721 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 121 PM 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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130 pm update... Lots of energy in the atmosphere. A mesoscale analysis, downward sloping motions out of the NE are eroding the overcast cloud cover across the region while putting an end to the showery weather as observed via satellite and radar traps. Whereas some mid to upper level energy round the broad troughing pattern is resulting in broken cloud decks and colder cloud tops pushing N and E with the mean flow. This as the coastal low lifts NE across the Gulf of ME into SE Canada. With the scattered to broken cloud decks we are seeing temperatures warm considerably. Many locations in the mid to upper 60s. Now the concern shifts towards whether enough heating emerges anabatically rising along the high terrain that we could see additional shower and perhaps even thunderstorm development N and W as presently observed over the N CT River Valley and especially the White Mountains. Decent cold pool aloft and with any diurnal heating we quite effectively mix out on up to H7 in most cases. So will have to monitor. This activity moving SW with the mean low to mid level flow. Can not rule out as the HRRR would suggest some potential activity into NW MA and the W CT River Valley. PoPs adjusted accordingly with the expectation of a SW to NE region of dry weather extending from Hartford CT on up into Manchester / Nashua NH. Some wet weather may linger along the E/SE coast per low clouds and drizzle. Otherwise, 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/... 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. && .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 /18Z SUNDAY THROUGH FRIDAY/...
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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/... 18z update... Today and Tonight...High Confidence. Trying to keep optimistic but surprised as how IFR is lingering across SE coastal terminals. May remain the norm with NE winds gusting around 25 kts through the overnight period with the additional threat of DZ/-RA. Otherwise all other terminals VFR with light N/NE winds. Low-end VFR cigs. Lesser confidence MVFR. Also watching N/W terminals only for this afternoon as to the possibility of SCT SHRA and low risk TSRA. Monday...Moderate Confidence. Low-end VFR cigs with MVFR across E/SE coastal terminals. Will heighten the risk of IFR to moderate keeping it confined to SE coastal terminals. -SHRA developing late, focus along the S coast as well as the N/W interior out into the CT River Valley. NE flow prevailing with gusts up to 20 kts especially over the E/SE coast. Monday Night...Moderate Confidence. -RA likely for all terminals. Deteriorating conditions into the evening hours and prevailing overnight. Mix of MVFR down to LIFR with NE winds prevailing, gusts upwards of 20 kts especially across the E/SE coastal terminals. A final note, there is a low risk of TSRA for SE coastal terminals. KBOS TAF...Pulling out MVFR and keeping cigs VFR with the low-end of the spectrum SCT per webcams shortly before 18z. Not much issue in thinking with landing on the 4`s if that be the case with NE winds prevailing, gusts up to 15 kts. KBDL TAF...Becoming SCT and dry and such trends should continue into the overnight hours. N winds with gusts limited to 15 kts. Will see a return of low cigs and wet weather late Monday with a continued downward trend into Monday night. Outlook /Monday Night through Thursday/... Tuesday...Moderate Confidence. Scattered showers will continue across the area with NE flow. An isolated TSRA 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. 130 pm 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...
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CT...None. MA...High Rip Current Risk until 10 PM EDT this evening for MAZ020- 022-024. RI...High Rip Current Risk until 10 PM EDT 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 ANZ250-251- 254>256.
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&& $$ SYNOPSIS...WTB/GAF NEAR TERM...Sipprell SHORT TERM...WTB LONG TERM...GAF AVIATION...Sipprell/GAF MARINE...WTB/GAF

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