Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 240613 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 213 AM EDT Tue Apr 24 2018 .SYNOPSIS...
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High pressure remains in control today bringing dry weather with mild daytime temperatures. Low pressure approaches and then passes through New England tonight into Wednesday night, bringing rain to the area. Another weak low pressure center may bring another round of showers to the area Friday night.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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150 AM Update... Other than patchy low clouds and fog reported from KMVY over the last several hours, skies were partly cloudy on average, with more high clouds moving in across the region from the SW as seen on latest GOES-East Night Fog and RBG Nighttime Microphysics products. Noting mainly light southerly or calm winds at most locations as high pressure ridge keeps low pres gradient across NE CT/RI/SE Mass, though a few spots still reporting SW winds up to 10 kt at 05Z. Dewpts were mainly in the 20s, except mid-upper 30s along the S coast, Cape Cod and the islands. Only exception was at KMVY where T/Td down to 26 degrees, the coldest spot across the region at 05Z. Will continue to see high clouds stream across the region from low pressure across E TN/KY as seen on latest satellite trends. Will continue to monitor for more patchy fog along the immediate S coast as T/Td spreads lower especially across the outer Cape and islands. Will also continue to monitor temp trends across SE Mass with the onshore winds off the milder ocean waters.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 AM WEDNESDAY/...
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Today... As the surface high moves further offshore, Tuesday will bring developing S to SW wind. A sea breeze is possible along east coastal MA for part of the day, however as the SW flow increases some during the afternoon, the east coastal sea breeze should come to an end. Mostly sunny skies expected for much of the day, with increasing clouds during the afternoon. A slightly warmer day with highs in the 60s across much of the area, some locales may reach 70 degrees. The cooler area will be the immediate south coast of MA/RI, where the persistent S wind will keep highs in the upper 50s to near 60. Tonight... Models show mid level ridging moving east of our area while deep trough currently over the lower Ohio/Mississippi Valleys works its way eastward. This pattern shift prompts a moisture-rich low pressure system to track eastward towards the Delmarva coastline. Moisture well ahead of this system will result in skies becoming cloudy during the evening, but it will take some time to moisten the column with respect to any precipitation. Expecting rain to become likely after midnight. PWATs during the overnight increase to 1 to 1.3 inches, so some moderate rainfall possible but generally thinking rainfall of a tenth to half inch prior to 12Z Wed. Cloud cover and increasing dew points will keep overnight lows somewhat milder, lows in the low to mid 40s for much of the area.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * Wet weather Wednesday, diminishing Wednesday night * Another round of showers possible Friday night and late Saturday Discussion... The 23/12Z operational guidance has come into better agreement with the details into Thursday. Fairly good overall agreement thereafter, although the Canadian model really goes off on its own later this weekend. Preferred a solution more like the GFS and ECMWF camp. Further prefer an ensemble mean approach, especially after Thursday. Wednesday and Wednesday night... Essentially the same story from the past few days. Multiple waves phase in the vicinity of the central Appalachians, or perhaps into the Mid Atlantic. Coastal low develops and tracks north through southern New England Tuesday night into Wednesday night. This will mean a period of wet weather for our region. Modest elevated instability still present, so cannot dismiss the possibility of isolated thunderstorms. Still looking like a general one half to one inch of rainfall when all is done. Locally heavier amounts possible in any persistent/slow-moving thunderstorms. Thursday through Friday... Except for possibly widely scattered late Thursday afternoon or early evening instability showers over the NW higher terrain, it looks dry Thursday afternoon through at least most of Friday. Confidence has increased of at least most of daytime Friday remaining dry. Friday night... A weak coastal low pressure may pass by just close enough for a risk of showers late Friday into Friday night, mainly across southeast MA and RI. Also will have to monitor the progress of a cold front associated with a low pressure in the St. Lawrence valley, which could also bring a chance for showers across the western half of southern New England late Friday night. Confidence remains rather low on these details, so later forecasts may change. Rest of this weekend... A cold front associated with a northern stream trough may result in scattered showers Saturday, but confidence in details remains low. Monday...High pressure expected to build in with drier weather. && .AVIATION /06Z 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/...High confidence. Overnight...VFR with SCT-BKN high clouds streaming in. Light S-SW or calm winds. Low to moderate risk of MVFR VSBYS in patchy fog across outer Cape Cod, KMVY and KACK. Today...VFR. Prevailing wind from the S-SW, increasing to around 10 kt by midday. Tonight...Mainly VFR. Patches of MVFR conditions after midnight, with local IFR possible towards daybreak across CT valley. -RA moving across the area by around midnight across the CT valley, then shifting E after midnight. Wednesday...Conditions lower to IFR from W-E by midday, with local LIFR possible along S coastal terminals. SE wind gusts up to 25-30 kt across Cape Cod and the islands Wed afternoon. Isolated TSRA. KBOS Terminal...High confidence in TAF. Low risk for possible brief sea breeze late morning to midday today before S-SW winds increase. KBDL Terminal...High confidence in TAF. Outlook /Wednesday night through Saturday/...High confidence. Wednesday Night: Mainly IFR, with local MVFR possible. Breezy. RA likely, tapering off to SHRA. Isolated TSRA possible. Patchy FG. Thursday: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA. Thursday Night through Friday: VFR. Friday Night through Saturday: VFR. Slight 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 Tonight/...High confidence. Overnight... High pressure across the waters with southerly winds 10 kt or less, seas 1 to 2 feet on the outer coastal waters. Good visibility. Today... S-SW wind increasing over the course of the day to 10-20 kts. Sea breeze along east coastal MA possible late morning or midday, then S winds should prevail as they strengthen. Seas 1 to 3 feet. Tonight... SE winds less than 25 kt. Seas locally approaching 5 ft, especially on the southern outer coastal waters. SCA headlines may be needed. Rain showers becoming likely towards daybreak. Outlook /Wednesday through Saturday/...High confidence. Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Rain, isolated thunderstorms, patchy fog. Areas of visibility 1 nm or less. Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 13 ft. Rain likely, chance of rain showers, isolated thunderstorms, patchy fog. Local visibility 1 nm or less. Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 10 ft. Slight chance of rain showers. Thursday Night: Winds less than 25 kt. Areas of rough seas. Friday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft.
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&& .EQUIPMENT... The NOAA Weather Radio transmitter serving Providence is 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. The transmitter serving Hyannis is back in service. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/NMB NEAR TERM...Belk/EVT SHORT TERM...NMB LONG TERM...Belk AVIATION...Belk/EVT MARINE...Belk/EVT/NMB EQUIPMENT...Staff

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