Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 081056 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 656 AM EDT Sat May 8 2021 .SYNOPSIS... A few showers are possible today, but most of the day should be dry, as a coastal low passes offshore and another weak low pressure moves into the Great Lakes. A brief period of fair and seasonable weather for Sunday beneath high pressure. A wave of low pressure likely brings a period of appreciable rainfall Sunday night into Monday morning, followed by a dry but cooling trend Tue and Wed. Dry and seasonable weather is possible Thursday, before yet another round of rain is possible Thursday night into Friday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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7 am update... Cloudy skies prevail this morning and will continue through the day. Satellite shows the offshore low well displaced enough that we shouldn`t see any precip from it. Could see a few sprinkles in western MA this morning, but the appreciable showers don`t appear until the afternoon. No significant changes to the forecast. Previous Discussion... A mishmash of weather features today. Nothing particularly strong, which would make this forecast a little easier. Starting out the day with a weak surface ridge, along with a weak mid level inverted trough extending back to the Great Lakes. Expecting yet another weak mid level shortwave to arrive later this afternoon. Put it all together, and there is a risk for some showers, but not likely a widespread rainfall. The greatest risk for showers will be from late morning into this afternoon. Yet another day of onshore flow and clouds. Below normal temperatures continue.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... Weak surface ridging should slowly develop across southern New England tonight into early Sunday. Some mid level drying with the corresponding subsidence should mean showers end near or shortly after sunset. These drier conditions should hold into Sunday morning, and perhaps last all day for most of our region. Another low pressure will approach from the southwest late in the day. Thinking an increasing risk for rainfall during the late afternoon and evening hours. This will be mainly across the western half of southern New England. It is possible this timing may change with later forecasts. Gut feeling is precipitation arrival timing may be slower than current forecast. Below normal temperatures continue. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... Highlights... * Seasonable to slightly cooler than normal temperatures through next week * Rain returns late Sunday into Monday * A few scattered showers Tuesday then drier through at least Thursday Details... Sunday night and Monday... A mid level shortwave and surface low approach from the Ohio Valley on Sunday night into Monday bringing the returns of widespread rain chances, mainly Sunday night into Monday morning. The warm front lifts north after sunset on Sunday bringing isentropically forced rain showers to much of southern New England. This front together with a PWAT plume ~1 inch and 40-50 kt low level jet will bring a widespread decent soaking on the order of 0.25 to 0.75 inches under the heavier bands. Whether the heavier rain falls over the south shore or further north will be honed in on in future updates, heavily dependent on the exact track of the low and surface warm front. For now, most guidance would suggest we remain on the cool side of the low. After 12-15Z, drier air pushes in above 800 mb bringing the widespread rain to an end, so the second half of Monday should be drier; could even see some breaks of sun. Temperature- wise highs won`t get out of the low 60s. Tuesday through Thursday... This will be a mainly dry stretch, with a few scattered showers mixed in, mainly on Tuesday. Behind the departing system from Monday a cool and drier northwest flow kicks in with a 30 kt low level jet between the departing low and incoming highs. So, should see a breezy day, gusting 15 to 20 mph. The upper level trough and cold pool move overhead, so should see some widely scattered instability showers. This cold airmass (-3 to -4 C at 850 mb) will be brief, but passing overhead Tuesday night into Wednesday. Thus, low temps will take a dip back into the 30s for much of the interior; low to mid 30s at higher elevations. Drier air brings clearer skies Wednesday, so sunshine together with a rapidly moderating airmass will bring quickly rebounding temps, back into the 60s. Thursday a high pressure ridge moves in with a much warmer airmass. 850 mb temps return to +3 to 4 C, allowing for highs in the upper 60s. Friday into the weekend... Our next shot at some rain comes around next Friday with an approaching shortwave, but confidence is low. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 12Z update... High confidence. Mostly VFR through Sunday. Increasing risk for showers today. Scattered MVFR in SHRA is possible across the western half of southern New England late this morning and afternoon. Relatively light onshore flow becomes variable this evening, then generally light westerly flow late tonight through Sunday. KBOS TAF...High confidence. KBDL TAF...High confidence. Outlook /Sunday Night through Wednesday/... Sunday Night: Mainly VFR, with local IFR possible. Breezy. RA. Monday: Mainly VFR, with local IFR possible. Breezy. Chance RA. Monday Night: VFR. Slight chance RA. Tuesday through Wednesday: VFR. Breezy.
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&& .MARINE... Weak high pressure near the Maritimes will maintain relatively light winds and seas across the waters through today. There is a small chance for 5 foot seas across the southern outer coastal waters today, especially south and east of Nantucket. While it is marginal, will be issuing a Small Craft Advisory for the southern outer coastal waters as seas should build, especially tonight into Sunday. Outlook /Sunday Night through Wednesday/... Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Rain. Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Chance of rain. Monday Night: Winds less than 25 kt. Areas of rough seas. Tuesday: Winds less than 25 kt. Seas up to 5 ft. Tuesday Night: Low risk for Small Craft Advisory winds with gusts up to 20 kt. Seas up to 5 ft. Wednesday: Winds less than 25 kt. Seas up to 5 ft. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT Sunday for ANZ254-255. Small Craft Advisory from 5 AM to 8 PM EDT Sunday for ANZ256.
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&& $$ SYNOPSIS...Belk/BW NEAR TERM...Belk/BW SHORT TERM...Belk LONG TERM...BW AVIATION...Belk/BW MARINE...Belk/BW

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