Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 222019 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 419 PM EDT Thu Sep 22 2016 .SYNOPSIS... Low pressure moves along the U.S./Canada border tonight. This will bring a cold front across southern New England Friday afternoon and evening with scattered showers and isolated thunderstorms. Cool and dry weather will follow this weekend into early next week. A slow-moving low pressure and cold front could lead to some showers late next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... High pressure will move offshore as low pressure moves eastward along the U.S./Canada border to Maine. The changing airmass will remain north of the area through the night, so quiet weather is expected once again. Decent radiational cooling is expected with calm winds and clear skies so lows will drop into the mid 50s to around 60. Localized patchy ground fog is possible. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Friday...Low pressure in Maine will move into the Maritimes, bringing a cold front south through the region. Moisture is rather unimpressive ahead of the front, so expect any showers and storms that develop to occur behind the front. Friday will start off with clear skies but clouds increase from north to south as the front works its way through during the afternoon. Behind the front, deep layer moisture increases with K indices climbing above 30 and Showalter indices dropping below 0. Scattered showers and an isolated thunderstorm or two are possible during the afternoon, mainly north of the Massachusetts Turnpike. These will be hit or miss showers, nothing even close to drought busting. With the front not reaching the south coast until after sunset, expect temperatures to climb into the 80s once again. 925mb temperatures are a degree or two lower than on the 00Z model runs so not sure that upper 80s are likely but with decent sun and heating allowed throughout the day, it`s not unreasonable that it may occur. Friday night...The front will move offshore around 00Z and winds will have shifted to the north across all of southern New England. Showers and an isolated thunderstorm are still possible, with the best chance now south of I-90. Any activity that does occur will likely come to an end shortly after midnight. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Highlights... * Cool and dry weather follows for this weekend into next week. * Patchy frost possible for some interior locations Sunday night. * Seasonable temperatures late next week Overview and model preferences... Still looking at a significant pattern shift for this weekend. Expecting a mid-level cutoff low to linger over the Maritimes. This cutoff gets shunted out to sea during the middle of next week. Another open, mid-level trough should arrive sometime late next week. Guidance is in rather good agreement with the timing of pushing this cutoff low out to sea. Although the GFS and GEFS are a bit slower to do so than the ECMWF. Always leery of model timing with cutoff lows, especially anomalously strong ones. Will favor an ensemble approach biased more toward the slower GFS. Details... Saturday... High pressure starts to nudge south from Quebec and Ontario. The arrival of drier air should mean a mostly rain-free day. Some early clouds across southeast New England should dissipate through the morning. A noticeable temperature drop from Friday. How much of one will depend on how quickly the clouds dissipate. Below normal temperatures Saturday night. If winds decouple fast enough, will likely see some patch frost develop across portions of the east slopes of the Berkshires. Low confidence on frost formation. Sunday and Monday... The core of the colder airmass takes over, resulting in below normal temperatures for this portion of the forecast. Dry conditions are expected, thanks to subsidence from the high pressure. May need to watch for isolated frost patches Sunday night, but this aspect remains a low confidence aspect of this forecast. Tuesday and Wednesday... There is the possibility for a weak warm front to linger near our region. Moisture is lacking, so not looking at a tremendous risk for showers. Kept a risk of isolated showers in the forecast for now, and even that may bee too high. More seasonable temperatures during this time. Thursday... Another mid-level trough and a cold front may approach. Low confidence forecast, as the timing may change. Moisture increases slightly, so mentioned a chance of showers. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through 00Z...High confidence. VFR. Tonight...High confidence. VFR, except for some late night and early morning patchy valley fog in the typically prone locations. Friday...High confidence. VFR cigs lowering from north to south in the afternoon. Scattered showers and possibly an isold t-storm developing aft 18z north of the pike where patchy MVFR cigs are possible toward evening. Friday night...Moderate confidence. Mix of MVFR/VFR in scattered showers and fog. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Saturday through Tuesday/... High confidence. Mainly VFR. Isolated to scattered showers possible Tuesday. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. High confidence. High pressure moves offshore tonight, allowing seas to build ahead of a cold front that will move across the waters Friday and Friday night. We may see isolated 5 foot seas late Friday into Friday night, but conditions are rather marginal so have not issued any Small Craft Advisories quite yet. Southerly winds will shift to the north behind the front on Friday but will remain below 25 kts. Outlook /Saturday through Tuesday/... Saturday into Sunday...Moderate confidence. N to NW winds expected, with gusts up to 25 kt possible. These persistent winds, combined with swell from Karl well offshore, will yield 5-7 ft seas, especially across the outer coastal waters. Small craft advisories may be needed. Winds and swells gradually subside late Saturday through Sunday. Monday into Tuesday...High confidence. High pressure moves over the waters, mainly quiet boating weather expected. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Belk/RLG NEAR TERM...RLG SHORT TERM...RLG LONG TERM...Belk AVIATION...Belk/RLG MARINE...Belk/RLG

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