Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 281120 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 720 AM EDT Wed Sep 28 2016 .SYNOPSIS... A stalled front south of New England will keep the threat of showers through this evening mainly along the coast. Onshore winds may also bring patchy drizzle and fog through tonight. A cool and unsettled pattern will persist into the weekend, before slow improvement early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 730 am update...No major changes to the forecast. Strong high pressure across Quebec and the Maritimes will cause surface ridging to continue to build SW across western areas and into SE NY/N NJ today. With a rather tight pressure gradient, will see NE winds increase during the day. Gusts up to 25-30 mph, highest during the afternoon along the coast. Noting some showers lingering near and S of Nantucket early this morning, but these should slowly push SE during the day as the ridge sinks S. Also can not rule out scattered showers and patchy drizzle developing during the day with the onshore flow and deep low level moisture. Have carried chance POPs through most of the day. With the increasing onshore flow, temps are not expected to rise much today. Expect highs only in the upper 50s to lower 60s, maybe a little bit milder across the lower CT valley this afternoon. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Tonight and Thursday... Spotty showers and patchy drizzle may linger tonight across central and eastern areas with persistent onshore winds keeping low level moisture in place. Should be mainly dry across the CT valley, but could even see a few showers there as well. Gusty NE winds continue along the coast with lows in the upper 40s across the higher inland terrain ranging to 55-60 along the immediate coast. For Thursday, more of the same, though not quite as much shower activity as least through midday. As H5 cutoff low pressure digs across the Great Lakes southward to the OH valley, stagnant pattern will remain in place through the day. However, with the developing mid level southerly flow, may see moisture work toward the region during the afternoon with a renewed chance for showers across central and southern areas. Temps will be a bit milder Thu with highs ranging from 60-65 across most areas. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... */ Highlights... - A cool, dreary, wet-weather pattern through Sunday - High pressure with cooler and drier conditions into next week - Keeping an eye on the tropics, monitoring Invest 97L */ Discussion... Second the previous forecast discussion in relying on ensemble means and probabilistics towards handling deterministic model struggles with closed cut off lows. Detailed below, going forecast will be a consensus of the broader perspective rather than particular details of any one solution. */ Details... Thursday Night through Tuesday Morning... Wet weather forecast mainly from early Friday morn through Sunday. Looking at a period of on again off again rain with embedded heavier showers (further details below). Could see total rainfall amounts in excess of 2 inches for parts of S New England though spread over a wide period of time. Thus low confidence with respect to flooding issues other than the typical nuisance, poor-drainage within urban centers. An overall wet and dreary period with cooler air associated with high pressure to the N over SE Canada undercutting an over- running event, likely conditions will be unseasonable beneath a deck of low clouds, stratus with fog and visibility issues mixed in, especially during the overnight periods. Too early to go into specifics, just going to broad-brush this one. Evaluating in more detail, expect the closed cut off low wobbling across the Ohio River Valley to undergo a mature to dying phase as it latches into and trowals back warm-moist sub-tropical air. This and attendant mid-level energy, will see the evolution of an over- running event along a warm-frontal T-occlusion that emerges S/E of New England into the Gulf of Maine. Anomalous isentropic convergent upslope along the 295-315K surfaces, also seen within H925-85 flow, of high theta-e air with pwats +2 inches, expecting periods of rain with embedded heavier showers to develop early Friday morning N of the T-occlusion associated mainly with strong convergent low-level forcing. With rains overspreading S New England as under-cutting NE flow prevails associated with high pressure over SE Canada. Expect dreary, cool conditions in addition to the wet weather as there will be lots of low-level moisture trapped beneath the inversion around H8 associated with downstream ridging. This pattern is likely to maintain through Saturday with the mid to upper level ridge associated with the Atlantic High holding stout, perhaps possibly longer as models have slowed the progression of the dying phase of the closed cut off low as a positively tilted trough into early next week. Difficult to shrug off the blocking amplitude of the downstream ridge. The transition of airmasses comes down to the upstream influence of the ridge-trough-ridge pattern extending from the NE Pacific into the Central CONUS. It is during this time- frame into Sunday that we begin to transition from a low- to mid- level forcing event along a kinked warm-frontal occlusion as heights fall and there is an increasing measure of diffluence aloft. Worth noting though is how effectively cooler air associated with surface high pressure remains dammed in place. Continued cool and dreary conditions expected. Per a consensus of forecast guidance, bulk of the synoptic exodus occurs around Sunday night into Monday as sub-tropical moisture is pushed offshore with drier air wrapping into the system ahead of a more continental polar airmass and associated cold front. Tuesday onward... High pressure filters S out of Canada and we see the return of cool, dry conditions with N winds prevailing. Then much of the focus turns towards Invest 97L. A consensus of forecast guidance concedes that the storm will strengthen as it moves into the warmer waters of the Caribbean. Where it goes from there and associated impacts to it and/or to particular locations remains uncertain. At 7+ days out in the forecast, there`s little to no skill in forecasting. Best advice is to keep evaluating the latest forecasts and maintain an awareness such that you`re not caught off guard and can prepare accordingly if circumstances arise. Don`t jump on any one particular solution. && .AVIATION /12Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...Moderate confidence. 12z update... Today... Widespread MVFR-IFR cigs with minor reductions in visibility down to MVFR, lowest S/E with the prevailing NE winds gusting upwards of 25 kts, strongest along the E coast. Some improvement towards midday across the interior upwards of low-end VFR, could also go from OVC to BKN, low possibility of SCT, seeing some sunshine in the mix. Best chance across the interior. Will keep conditions low along the coast. Tonight... MVFR-IFR cigs lowering down to LIFR especially across higher terrain. MVFR vsbys with patchy fog / drizzle continuing. Thinking lower down to IFR around midnight along the coast. NE winds continue with gusts up around 25 kts, strongest along the coast. Thursday... Areas of IFR-LIFR cigs early morning, then mainly a mix of MVFR-IFR cigs the remainder of the day. Slight improvement possible across the interior as vsbys improve to MVFR-VFR. Continued NE winds 25 to 30 kts, strongest along the SE coast towards late. KBOS TAF...MVFR cigs overall but can not rule out IFR, which is expected as we go into evening and overnight. Will keep with VFR vsbys through today with patchy drizzle as NE flow remains persistent. Overall moderate confidence. KBDL TAF...IFR cigs this morning are expected to improve to MVFR towards midday. May see a return to IFR conditions overnight. Moderate confidence. Outlook /Thursday Night through Sunday/...Moderate confidence. Overall a persistent N/NE flow with 30 kt gusts possible along with LLWS issues Thursday night through Saturday morning. Expect a mix of MVFR-IFR with likely scattered to widespread SHRA activity. Though winds diminish through Saturday into Sunday though persistent out of the NE, low cig and vsby conditions continue. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High confidence. 730 am update... Today...S-SE swells up to 5-6 ft will subside briefly on the southern outer waters, only to build again as NE winds increase. Gusts up to around 25 kt. Small crafts in effect for all waters including Boston Harbor and Narragansett Bay. Visibility restrictions in patchy fog / drizzle, as well as scattered showers. Tonight and Thursday...Persistent NE winds will continue through the period with gusts up to 25-30 kt. Seas will build up to 7-9 ft, highest on the eastern waters with long onshore fetch. Patchy drizzle and a few showers will continue tonight, then will become more isolated early Thursday. More showers may move in across the southern waters late Thu with more vsby restrictions. Outlook /Thursday Night through Sunday/...Moderate confidence. Persistent N/NE flow with gusts to potentially gale force around Friday morning. Will see wave heights subsequently build upwards of around 8 to 10 feet on the outer waters. Strongest wave action is likely over the E/SE waters and over the far SW waters. Visibility restrictions more than likely given anticipated wet weather. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 5 PM EDT Thursday for ANZ230>237. Small Craft Advisory until 5 PM EDT Thursday for ANZ250-251- 254>256. && $$ SYNOPSIS...Sipprell/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...Sipprell AVIATION...Sipprell/EVT MARINE...Sipprell/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.