Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 221949 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 349 PM EDT Sun Apr 22 2018 .SYNOPSIS... High pressure remains in control through Tuesday bringing dry weather with moderating temperatures. Wet weather returns Wednesday into Thursday as low pressure moves through our region. Unsettled weather continues into the weekend, but not a washout. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... Just about as quiet as it gets around here weatherwise with high pressure in control. Satellite imagery shows clear skies around region with nearest (high) clouds in PA and southern NJ. Deep mixing to nearly 850 mb has prevented sea breezes from developing so far this afternoon. However, model guidance suggests winds aloft will weaken just enough to allow a weak sea breeze to develop along E MA coast and a slightly stronger SW sea breeze along south coast from mid to late afternoon. Mixing has also brought drier air to surface, as dewpoints have fallen into teens and lower 20s, resulting in relative humidity values dropping to less than 20 percent. Dewpoints will gradually recover through this evening as mixing subsides. Otherwise, clear skies and light winds tonight with patchy valley fog. Leaned closer to MOS for lows which tend to perform well in these situations. Lows drop back into 30s to around 40 with some patchy frost inland. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... High pressure becomes centered over SNE Monday. Once again plenty of sunshine with light winds, and coastal sea breezes will get underway by their usual late morning time frame. This will give way to S/SW flow Monday night as the high shifts offshore, with some increase in high clouds late. Stayed close to MOS with highs in the 50s/60s Monday, perhaps approaching 70 in CT valley, and lows falling back into 30s to near 40 Monday night. && .LONG TERM /TUESDAY THROUGH SUNDAY/...
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*/ Highlights... - Wet and breezy midweek - Perhaps a reprieve Friday - More showers possible Saturday Overview and model preferences... 22/12Z guidance remains in decent overall agreement through this portion of the forecast, although more detail differences arise after Wednesday. Generally expecting two mid level waves to phase over the Ohio valley/central Appalachians towards Wednesday. This amplify the resulting trough, and steer a low pressure closer to southern New England Wednesday into Thursday. Near normal temperatures much of this period, except for Wednesday. Continue to favor an ensemble approach for this portion of the forecast, especially after Wednesday. Details... Dry weather through Tuesday, with a large high pressure over the Maritimes. Some question as to how quickly this high pressure will move offshore. Latest guidance has sped up the arrival of rainfall into late Tuesday night. Some surface ridging noted over southern New England Wednesday morning, so this might be too fast. Preferred a slower arrival to rainfall than the latest guidance for this reason. Good setup for a soaking rain Wednesday into Wednesday night. This looks to be our most likely period of wet weather during the next 7 days. Southern New England should be in the dry slot of this system Thursday, although there could be some lingering showers north of the Mass Pike Thursday morning. A brief dry period possible Thursday night into early Friday, before another low pressure moves into the Great Lakes. This system should be close enough where there would at least be a chance for some showers. Not looking like a washout, though. High pressure may start to arrive Sunday, leading to drier weather.
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&& .AVIATION /20Z 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 Night/...High confidence. Sea breeze potential still questionable along E MA coast this afternoon as winds aloft have been just strong enough to maintain W/NW flow. However, there should be some weakening in winds later this afternoon to allow sea breeze to develop between 20z-23z. Confidence is higher for south coastal sea breeze which should get underway around 20z as well. VFR. Light W/NW winds prevail tonight with local MVFR/IFR visibility in patchy valley fog. Higher confidence in sea breezes along both coasts Mon. KBOS Terminal...Moderate confidence in TAF. E sea breeze expected 20z-23z but if it does not occur, winds will veer to N. KBDL Terminal...High confidence in TAF. Outlook /Tuesday through Friday/...High confidence. Tuesday: VFR. Tuesday Night: Mainly VFR, with local IFR possible. Chance RA. Wednesday: MVFR/IFR conditions possible. Breezy. RA. Wednesday Night: Mainly VFR, with local IFR possible. Breezy. Chance SHRA, chance RA. Thursday: VFR. Breezy. Slight chance SHRA. Thursday Night: VFR. Breezy. Friday: VFR. Breezy. Chance SHRA.
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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 Monday Night/...High confidence. High pressure builds over waters with light winds, flat seas, and good visibility. Only concern for recreational boaters is for sea breezes along South Coast this afternoon with 15-20kt gusts and choppy seas near shore, especially when opposing outgoing tide. Similar conditions Monday. Outlook /Tuesday through Friday/...High confidence. Tuesday: Winds less than 25 kt. Tuesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain. Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Rain. Wednesday Night: Winds less than 25 kt. Rough seas up to 12 ft. Chance of rain, slight chance of rain showers. Thursday: Winds less than 25 kt. Rough seas up to 9 ft. Thursday Night: Winds less than 25 kt. Areas of rough seas. Friday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers.
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&& .EQUIPMENT... NOAA Weather Radio transmitters serving Providence and Hyannis are out of service due to phone line problems. The phone company has prioritized the issues and is working to get the weather broadcast back on the air as soon as possible. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/JWD NEAR TERM...JWD SHORT TERM...JWD LONG TERM...Belk AVIATION...Belk/JWD MARINE...Belk/JWD EQUIPMENT...Staff

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