Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 170207 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1007 PM EDT Thu Aug 16 2018 .SYNOPSIS... Showers and thunderstorms will be on the increase Friday into Saturday as a cold front approaches southern New England. This front moves through late Saturday, followed by mainly dry and cooler weather Sunday into Tuesday as high pressure builds in from the north. The humidity will return by Wednesday leading to the risk of more showers and thunderstorms. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 950 PM Update... Any precip from earlier this evening has ended across the region. Noting only a few spotty clouds in the W-NW flow aloft from SW NH southeastward across portions of N RI and E Mass, as seen on latest GOES-East RGB Nighttime Microphysics composite. Should see these clouds dissipate or push offshore through around midnight or so. May be seeing some patchy fog developing along the immediate S coast where the higher dewpoints remain, but will be spotty at best. Other than minor adjustments to bring conditions current, not much change to the previous forecast. Previous Discussion... Mostly clear skies expected through around 2 AM or so before clouds begin to approach from west. Lows will fall back to the 60s and lower 70s. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... * Potential for strong/severe storms later Fri into Fri evening * Localized wind damage/flash flooding possible * Isolated short-lived tornado also possible Showers and thunderstorms become more likely Friday, especially during afternoon and evening across interior, as front lifts back north thru SNE as a warm front. Models show good instability with MLCAPE up to 1500 J/kg but 0-6km shear is minimal, however it does increase later in day and especially Friday evening. Setup favors potential for a few strong/severe storms with localized wind damage. Also have potential for localized flash flooding as precipitable water values climb back to 2 inches or higher. We also need to be concerned with an isolated short-lived tornado late Friday afternoon/Friday evening given rather high 0-500m helicity near 100, low LCLs, and warm front nearby. Later Friday night, conditions become less favorable for organized strong/severe storms as warm front lifts into northern New England but showers/storms should make their way to coast due to approach of mid level short wave. Warm and humid conditions return with highs Friday in 80s and lows Friday night only falling back into upper 60s to mid 70s. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Highlights... * Showers/thunderstorms likely Saturday across a good portion of southern New England * Locally heavy rainfall possible, along with the potential for a few strong to severe storms Saturday * Mild to warm days and cool nights Sun/Mon/Tue * More humid with increasing risk of showers/thunderstorms Tue night/Wed 16/12Z guidance remain in decent overall agreement, with the typical detail differences towards the end of next week. In general, expecting the current heat and high humidity pattern to break for a time, about Sunday into Tuesday. Expecting the Bermuda high to move back out to sea, which will allow a mid level trough to settle over New England. This should mean dew points in the 60s (and perhaps upper 50s across the higher terrain), with high temperatures in the 70s. Unfortunately, this mid level trough will still mean at least a risk for periodic showers and thunderstorms. No single day would be a complete washout. There remains a low risk for stronger thunderstorms Saturday, mainly south of the MA Pike, which would be closer to the greater instability. Not a certainty, though. Will continue to favor a consensus approach to smooth over the less predictable details. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/... High confidence. Overnight...VFR. Expect dry conditions. May see brief spotty MVFR VSBYS in patchy fog across N central and W Mass after 08Z. Friday and Friday night...Scattered showers/storms develop in western New England Friday morning and head east, reaching coast Friday evening and continuing Friday night. VFR conditions expected most of the time but areas MVFR/IFR in showers/storms. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Friday Night through Tuesday/... Friday Night: Mainly VFR, with areas MVFR possible. Chance SHRA, chance TSRA, patchy FG. Saturday: Mainly VFR, with local MVFR possible. Chance SHRA, slight chance TSRA. Saturday Night: Mainly VFR, with areas MVFR possible. Chance SHRA. Sunday: Mainly VFR, with local MVFR possible. Breezy. Slight chance SHRA. Sunday Night through Monday: VFR. Slight chance SHRA. Monday Night: VFR. Tuesday: Mainly VFR, with local MVFR possible. Slight chance SHRA. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. Weak cold front stalls near or just S of Cape Cod overnight, with winds becoming light/variable before veering to S-SE Friday. Seas 3 ft or less. Increasing S winds expected Friday night with gusts up to 20 kt on south coastal waters, which may bring seas up to 5 ft offshore. Outlook /Friday Night through Tuesday/... Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, chance of thunderstorms, patchy fog. Local visibility 1 to 3 nm. Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, slight chance of thunderstorms, patchy fog. Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, isolated thunderstorms, patchy fog. Sunday through Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. Monday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Air Quality Alert until 11 PM EDT this evening for MAZ020- 022>024. RI...Air Quality Alert until 11 PM EDT this evening for RIZ006>008. MARINE...None. && $$ SYNOPSIS...Belk/JWD NEAR TERM...Belk/EVT SHORT TERM...JWD LONG TERM...Belk AVIATION...Belk/EVT/JWD MARINE...Belk/EVT/JWD

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