Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 202017 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 417 PM EDT Thu Apr 20 2017 .SYNOPSIS... A warm front moves north across our region late tonight into Friday morning, and will be accompanied by another round of rain. Drier and quiet for Saturday. Rain skirts by to our south Sunday, with another shot of some rain late Tuesday into Wednesday. Otherwise, near normal conditions as temperatures moderate up against an east onshore flow. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... Not a lot of change from previous forecast. Still thinking greatest rainfall risk will be along and north of the Mass Pike, and most likely to fall after midnight Friday. Cannot rule out scattered showers west of the CT River between 8 PM and midnight. Temperatures will slowly fall tonight with a freshening east flow in place. Expecting a switch from the diurnal clouds we have this afternoon, to a lower marine stratus moving west into southern New England. These lower clouds should keep min temperatures slightly above normal. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
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Primary low pressure passes by our region well to our north, but close enough to try to push a warm front across southern New England late Friday into Friday night. Thinking this front will not make it completely through our region for a couple of reasons: 1. a high pressure over Nova Scotia will maintain an east to southeast flow near the surface and, 2. a weak frontal wave should develop just south of the islands friday night. Both of these factors should force this boundary to stall over eastern MA, for at least a time. The main limitation for rainfall will be the timing of a mid level dry slot, which should work its way from west to east along the south coast during the afternoon and evening. At the very least, expecting coverage of showers to diminish during the afternoon across northern CT, RI into southeast MA late Friday afternoon and evening. Eventually, the rain should move northeast of our region as this dry slot widens late Friday night. Latest guidance continues to advertise very marginal instability, so have kept thunderstorms out of the forecast. East to southeast flow continues. There could be gusts of 20-30 mph along the east coast, especially across Cape Cod and the islands, as well as Cape Ann. These onshore winds will mean high temperatures about 5-10 degrees below normal Friday, with near to slightly above normal low temperatures Friday night.
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/...
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Big Picture... Periods of rain through Tuesday and parts of Wednesday, then a high pressure builds in from the south returning dry and warmer weather. Details... Saturday... Saturday will be mostly dry, with potential isolated showers in the early morning hours as the low pressure system that affected the region Friday moves offshore. Skies will likely remain cloudy throughout the day, with a chance of broken clouds in the afternoon and evening. Temperatures will be seasonable with temps ranging in the 50s across Southern New England. Overnight temperatures will be in the 40s through the night as winds remain northwesterly with occasional wind gusts up to 10 mph. Sunday... Sunday will be mostly cloudy as a shortwave trough progresses across the region ahead of a cold front located over the Great Lakes. A low pressure area located over the Carolinas may advect some moisture into our region, possibly producing periods of rain along the southern coast. Sunday temperatures will range in the 50s to low 60s across the region. The Connecticut River Valley will likely see the warmest temperatures with the Cape and North Shore remaining in the 50s. With weak southwesterly winds, overnight temperatures will remain in the 40s across Southern New England. Monday... The cold front will make its way through New England Monday morning, causing winds to gust up to 20 mph behind the front. Afternoon temperatures will be seasonable with highs in the upper 50s. Winds will become northerly Monday evening after the frontal passage, dropping evening temperatures into the upper 30s and lower 40s across New England. There is a chance for light showers along the southeastern coast of New England late Monday evening as the cold front moves offshore and a warm front approaches from the south. Tuesday through Thursday... Tuesday will be windy along the southeastern coast of New England as the low pressure approaches the region from the south. Northeasterly winds will be advected down into the New England making for cooler temperatures through the period. Temperatures are expected to remain in the 50s throughout the day, with low temperatures in the 40s. Winds will diminish Wednesday inland, but remain strong along the coast. Winds may gust up to 25 mph at times as the low pressure skims the eastern coast of New England. Afternoon temperatures will be slightly warmer than Tuesday, with highs in the low 60s, due to a southerly windshift. The chance of rain persists through early Thursday morning as the low pressure continues to hug the eastern coast due to a strong low level jet. A high pressure area will build in behind the low pressure system, returning dry weather and warmer temperatures. Temperatures will return into the upper 60s for Thursday.
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&& .AVIATION /20Z THURSDAY THROUGH TUESDAY/...
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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 Friday Night/...Moderate confidence. Through 00Z... latest visible imagery showing a bank of marine stratus over the ocean, heading west. This stratus will impact the Cape and islands first, with MVFR to IFR CIGS. Elsewhere in southern New England, mainly VFR CIGS with local MVFR CIGS. Tonight... Dry to start, but rain redevelops after 03z from west to east. Rain may be briefly moderate to heavy at times, particularly toward the NH/VT border with MA. MVFR to IFR CIGS become more widespread after 02Z from east to west. Friday... A mix of IFR/MVFR in rain with a drying trend 18z-00z from west to east. Southeast winds becoming gusty across eastern coastal MA from Cape Cod to Cape Ann during the afternoon. Friday night... BKN-OVC MVFR/IFR CIGS lingering, especially across eastern New England with a chance of -RA, VFR conditions likely develop in the CT River valley late. KBOS TAF...High confidence in trends, but somewhat lower on exact details including timing. Later portion of the evening push could be impacted by marine stratus. Continuing to monitor timing. KBDL TAF...High confidence in trends, but somewhat lower on exact details including timing. Outlook /Saturday through Tuesday/... Saturday..High confidence IFR becoming VFR along the southeastern coast of New England late morning as rain and fog dissipates. Mainly VFR across New England then follows throughout the day. Sunday...Moderate confidence VFR with a slight chance for MVFR along the southern coast of New England late Sunday morning due to possible rain showers. Northern Massachusetts will remain in VFR throughout the day. Monday...Moderate confidence. Mainly VFR with high pres. Tuesday...Moderate confidence. VFR to start will give way to a mix of MVFR/IFR toward the evening hours, first across S coastal terminals then spreading north.
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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 Friday Night/...High confidence. Increasing east winds tonight into Friday will also result in building seas, especially across the eastern coastal waters. Will be posting a Small Craft Advisory for these waters, soon. Areas of rain will overspread the waters after midnight, then gradually move out Friday afternoon into Friday evening. Visibility will likely be less than 1 mile at times through Friday afternoon in areas of fog. Fog should linger Friday night as well, but with slightly improved visibility. Outlook /Saturday through Tuesday/... Saturday...High confidence Lingering swell near 5-7 ft on the ocean waters will yield continued small craft advisory conditions, but mainly along the eastern waters. Some fog, but otherwise quiet boating conditions. Sunday into Monday...Moderate confidence High pres over the waters will lead to generally quiet boating weather across the region. Tuesday...Low confidence. The combination of persistent E-NE flow reaching around 25 kt and a building swell as a result will lead to Small Craft conditions mainly during the latter half of the day.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 8 AM to 10 PM EDT Friday for ANZ231- 232. Small Craft Advisory from 2 AM Friday to 8 AM EDT Saturday for ANZ250-254-255. Small Craft Advisory from 6 AM Friday to 8 AM EDT Saturday for ANZ251.
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&& $$ SYNOPSIS...Belk/Doody/Correia NEAR TERM...Belk SHORT TERM...Belk LONG TERM...Doody/Correia AVIATION...Belk/Doody/Correia MARINE...Belk/Doody/Correia

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