Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 291555 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1055 AM EST Tue Nov 29 2016 .SYNOPSIS... Rain will become heavy at times across Connecticut...Rhode Island and south of the Massachusetts turnpike this afternoon and early evening. A brief period of drying will cross the region late tonight into part of Wednesday morning. The next round of rain arrives Wednesday afternoon and night as low pressure moves across New England. Conditions will improve Thursday as the low moves into the Maritimes, followed by mainly dry and cooler weather for Friday through Sunday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... ***Rain will become heavy at times later this afternoon/early evening especially south of the MA Turnpike with typical urban poor drainage street flooding possible*** ***Southerly wind gusts of 40 to 50 mph expected this evening across the Cape and Islands*** 1035 am update... We allowed the freezing rain advisory to expire on time at 10 am as temps have risen above freezing across all of northwest and north central MA. Heavy Rain Threat... Otherwise, the main story will be the bands of heavy rain that will affect the region later this afternoon and evening. Steady rain across interior southern New England will overspread the coastal plain through early afternoon. Impressive low level jet of 50 to 60 knots and up to 70 knots along the southeast coast will combined with PWATS 2-3 Standard Deviations above normal to result in heavy rainfall. The heaviest rain looks to occur south of the MA Turnpike late this afternoon and unfortunately into the evening rush hour. This a result of strong low level jet along with an area of surface convergence associated with the wave of low pressure. This may result in typical urban poor drainage street flooding. There may even be an isolated thunderstorm or two near the south coast as strong low level jet combines with marginal elevated instability. Rainfall amounts through this evening look to average between 0.50 to 1.50 inches, but localized 2+ inch amounts can not be ruled out south of the MA Pike and especially near the south coast if any isolated convection is able to develop. Strong Winds... We opted to issue a wind advisory for southern Plymouth County as well as the Cape/Islands this evening. Despite the inversion a 60 to 70 knot low level jet near 925 mb should be able to mix down a few wind gusts between 40 and 50 mph, especially in bands of heavier rain. While the inversion will certainly be a limiting factor, given that the SST are still in the 50s it will be a less of a factor than a few months from now. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... 345 AM update... Tonight... Rain tapers off during the early evening from west to east. Rain will be heavy at times over RI and eastern MA until 00z-03z before ending. Isolated thunder possible during this time. As short wave and attending surface low move off the eastern MA shoreline a drying trend develops 03z-06z. However winds then drop off later at night and the combination of moist low levels from heavy rainfall across CT/RI and southeast MA may result in areas of dense fog. Guidance not hitting this very hard so confidence is low on areal coverage of any dense fog. Thus no headlines at the moment but something later shifts will need to monitor. Not nearly as cold as previous nights with lows only in the upper 30s to lower 40s inland and mid 40s to low 50s elsewhere. Wednesday... Dry weather and perhaps a few dim breaks of sunshine Wed morning in response to weak subsidence on backside of departing system. However upper air pattern is very progressive with next system bringing rain to the region by late Wed morning or early afternoon. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Highlights... * Rain will fall heavily at times Wednesday night as low pressure crosses the region * Conditions will improve during Thursday, with cool and blustery weather Friday through most of the weekend * Uncertainty continues for Sunday night and Monday regarding potential for another low pressure system Overview... Cutoff H5 low pressure center and associated long wave trough across the Great Lakes Wednesday night will bring another round of rainfall as surface low pressure crosses the region. This low will linger across southern Quebec into Maine then eventually the Maritimes late this week into the weekend as upper level steering currents tend to flatten out. Should see mainly dry but cool conditions during this timeframe. Another H5 low closes off across the SW U.S. during the weekend. 00Z model suite and associated ensembles continue to have wide divergence on their solutions for the evolution of this cutoff low into early next week. Details... Wednesday night... Areas of rain, heavy at times, will continue through around 06Z, as highest PWATs /on order of 1.25 to 1.5 inches/ move across. Expect the heaviest precip across E Mass possibly into RI, but should be steadily moving offshore as H85 jet up to 40-50 kt passes S of New England. The precip will begin to taper off across W Mass into N Central CT overnight as drier air wraps in as the low exits to the central Maine coast. Should see the main precip push offshore by daybreak, though showers may linger across eastern areas. QPF amounts overnight will range from 0.4" over the west to 0.75" along the E coast. Could still see some localized street flooding due to water backing up in leaf-clogged catch basins. Expect overnight lows mainly in the 40s, though will range to around 50 along the S coast. Thursday... Low pressure will exit to the Maritimes early Thursday, with drier W winds moving across the region. Noting area of good low level mixing through H85 moving into the region by around midday Thursday, so could see blustery conditions developing during the day mainly along the S coast and across the higher terrain. Will probably see diurnal clouds develop with the colder air aloft by midday through the afternoon. It will be a mild day as H92 temps do not begin to drop until Thursday afternoon. Highs will range from upper 40s across the E slopes of the Berkshires ranging to the mid and upper 50s along the coastal plain. Thursday night through Sunday... Will see mainly dry conditions, but it will be cooler with blustery winds. With H5 heights falling, may see a few weak short waves in the general W-NW flow aloft. Weak low pressure will pass across western Maine during Friday as well. May see some sct rain and/or snow showers across the E slopes of the Berkshires and possibly the northern Worcester hills during Friday. Temperatures will return to seasonal levels through the weekend. Sunday night-Monday... As 00Z models and ensembles continue to show a wide spread in their solutions during this timeframe, have very low confidence for this period`s forecast. The question lies in how the closed H5 low over the SW U.S. evolves, whether it opens up and becomes progressive as suggested by the ECMWF, or if it remains blocky and slows weather systems across the lower 48. Continued with a model compromise for this period with chance POPs. && .AVIATION /16Z TUESDAY THROUGH SATURDAY/...
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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 Wednesday/... This afternoon...Moderate to high confidence. Low end MVFR to IFR conditions overspread the region through early afternoon along with widespread rain. Heaviest rain affects CT/RI and SE MA from west to east between 20z and 02z and there may even be a rumble or two of thunder. LLWS will develop by late afternoon and continue into the evening with strong low level jet of 50+ knots. In addition...southerly wind gusts of 30 to 40 knots expected to develop this evening across the Cape/Islands. Tonight... Heavy rain with isolated thunder at 02z begins to exit offshore. LLWS at 00z weakens between 03z and 06z. Period of IFR begins to improve toward 06z. However as modest south winds shift to the west in the evening and then become light and variable areas of dense fog are possible after midnight. Moderate to high confidence on trends but lower especially on details of dense fog potential. Wednesday... Low risk of patchy IFR in dense fog. Otherwise VFR and dry weather in the morning gives way to IFR and rain for the afternoon. KBOS TAF...MVFR arrives around 15z and IFR about 21z along with moderate to heavy rain. Heaviest rain and risk of isolated thunder may slide south of Logan 21z-02z. KBDL TAF...MVFR arrives around 13z followed by IFR near 18z along with moderate to heavy rain. Outlook /Wednesday Night through Saturday/... Wednesday night...Moderate confidence. Expect IFR CIGS/VSBYS in areas of rain and fog with local LIFR CIGS. Periods of heavy rain likely through 06Z. Rain begins to taper off across the CT valley with CIGS improving to MVFR-VFR toward 12Z. VSBYS will also improve to MVFR. Thursday...Moderate confidence. MVFR-IFR CIGS will improve from W-E by mid morning, but lower CIGS may linger across the higher inland terrain through midday. CIGS may lower to 3000 ft around or after 21Z. VSBYS improve to VFR by around midday. Thursday night through Saturday...Moderate confidence. Mainly VFR CIGS. May see periods of MVFR CIGS across higher inland terrain at times. Gusty W winds expected mainly along the coast.
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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. Short Term /through Wednesday/... This afternoon and tonight...Moderate to high confidence. Low level jet of 60 to 70 knots develops by late afternoon/evening across our waters. Despite inversion, opted to upgrade many of our waters to Gales for 30 to 40 knot gusts. Heavy rain bands will probably allow for some gusts to mix down and with water temps in the 50s, inversion is not as strong as what we would see in a few months. Wednesday... Next wave of low pressure approaches from the southwest. E-SE winds develop along with another round of rain and fog. Outlook /Wednesday Night through Saturday/... Wednesday night...Moderate confidence. E-SE winds will veer to W-SW overnight. Gusts increase to 25-30 kt, highest along the southern open waters where seas will build up to 6-10 ft. Reduced vsbys in areas of rain and fog, beginning to improve on the southern waters toward daybreak. Thursday and Thursday night...Moderate confidence. W winds will continue, gusting up to 25-30 kt. Seas remain high on the southern waters, up to 6-10 ft over the outer waters. Visibilities improve by mid morning, and remain good through Thu night. Friday through Saturday...Moderate confidence. W-NW winds continue, with gusts to 25 kt at times. Seas AOA 5 ft will persist over the south coastal waters. Good vsbys.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Wind Advisory from 5 PM this afternoon to midnight EST tonight for MAZ021>024. RI...None. MARINE...Gale Warning from 4 PM this afternoon to 1 AM EST Wednesday for ANZ231>235-237-250-254>256. Small Craft Advisory from 2 PM this afternoon to 1 AM EST Wednesday for ANZ230. Small Craft Advisory until 1 AM EST Wednesday for ANZ236-251. && $$ SYNOPSIS...Nocera/EVT NEAR TERM...Frank SHORT TERM...Nocera LONG TERM...EVT AVIATION...Frank/Nocera/EVT MARINE...Frank/Nocera/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.