Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 291007 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 507 AM EST Tue Nov 29 2016 .SYNOPSIS...
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An approaching warm front will result in a widespread rainfall today across the region...beginning this morning then becoming 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.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/... 345 AM Update... Freezing Rain Potential... Rain overspreads the region later this morning from southwest to northeast in response to warm air advection on the nose of strong mid level jet. However cold/dry airmass lingers over the area this morning with temps at 3 am subfreezing across western and northern MA. This shallow cold layer will be slow to erode/dislodge especially with light northerly winds being reported now at BAF and HFD. Threat for freezing rain will hinge on timing/arrival of precip and if shallow cold air lingers long enough. Global and high res guid in good agreement that risk for freezing rain is greatest across northwest MA from about 10z to 14z. Thus will continue with freezing rain advisory for this region. As we know from past events it only takes a trace of freezing rain to yield icy roads. Elsewhere temperatures will warm to above freezing before rain arrives. Heavy Rain Potential... Plume of subtropical moisture overspreads the region this afternoon and early evening with PWATS surging up to +3 standard deviations from climo during this time. Strong jet dynamics will be acting on this anomalous moisture with 925 mb SSW jet increasing to +3 standard deviations by 00z as this low level jet clips the south coast. Global guidance in good agreement on widespread rainfall of 0.5 to 1.0 inches. While hi res guid including the NAM/RGEM/ARW and NMM all suggest some embedded convective elements from instability aloft yielding potential isolated rainfall amounts up to 2.0 to 2.5" pending areal coverage of elevated convection. Heaviest rain appears to fall from 20z west to 01z eastern MA. Good agreement on axis of heaviest rainfall from CT-RI and south of the Massachusetts turnpike. This will likely impact the late day/evening commute with minor highway and street flooding. Temperatures... Given the strong thermal advection leaned on the high res guid for highs today/this evening. ARW/NMM and NAM suggest late day/early evening highs of 55-60 from 00z-03z as warm sector overspreads much of the region. Warm front may not clear northern MA so places along and north of RT-2 may only warm into the lower 50s. For this morning...given the light winds and trapped low level cold air followed the colder MOS temps. Strong winds... Low level SSW jet of 50-60 kt overspreads RI and southeast MA 21z- 02z. However model soundings become inverted and preclude stronger winds aloft from mixing to the surface. Thus winds should remain below wind advisory criteria with most gusts 40 mph or less. However can/t rule out isolated higher gusts in heavier downpours. Although majority of wind gusts will remain below advisory criteria. Thus no wind headlines issued. However these modest winds will result in a windswept rain this evening for the coastal plain of MA and RI. && .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/...
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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.
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&& .AVIATION /10Z 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/... 1:15 AM Update... Thru 12z... VFR conditions at 06z will lower to MVFR around 12z across western MA along with the risk of freezing rain in this region. Elsewhere dry weather and VFR continues. Forecast confidence is moderate to high. After 12z... VFR to start except MVFR western MA along with risk of freezing rain across this region. Risk of freezing rain ends by 15z across western MA. Then by 18z much of the region is MVFR with moderate to heavy rain overspreading the area from SW to NE. Heaviest rain 21z-00z with widespread MVFR and IFR across the higher terrain. Low risk of isolated Thunder too 21z-00z. LLWS likely toward 00z as 50-60 kt SSW low level jet moves across the area. Forecast confidence moderate to high. Tonight... Heavy rain with isolated thunder at 00z begins to exit offshore. LLWS at 00z weakens 03z-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/... 345 am update... Today... Winds becoming SSW and increasing up to 30 kt toward sunset. Rain overspreads the waters later this morning from southwest to northeast. Heaviest rain with isolated thunder occurs 5 pm to 9 pm. Tonight... SSW winds up to 30 kt early this evening then shifting to west toward midnight and becoming light thereafter. Heavy rain early this evening tapers off before midnight. Wednesday... Next wave of low pressure approaches from the southwest. East to southeast 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...
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CT...None. MA...Freezing Rain Advisory until 10 AM EST this morning for MAZ002>004-008-010-026. RI...None. MARINE...Small Craft Advisory from noon today to 1 AM EST Wednesday for ANZ231-232-251. Small Craft Advisory from 10 AM this morning to 7 AM EST Wednesday for ANZ233>235-237-254>256. Small Craft Advisory from 2 PM this afternoon to 7 PM EST this evening for ANZ230. Small Craft Advisory from noon today to 11 PM EST this evening for ANZ236. Small Craft Advisory from noon today to 7 AM EST Wednesday for ANZ250.
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&& $$ SYNOPSIS...Nocera/EVT NEAR TERM...Nocera SHORT TERM...Nocera LONG TERM...EVT AVIATION...Nocera/EVT MARINE...Nocera/EVT

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