Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 030202 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1002 PM EDT Sun Oct 2 2022 .SYNOPSIS... A wave of low pressure will linger to our south for the first half of the week, which will keep onshore flow and perhaps some showers re-developing by Tuesday and/or Wednesday with the best chance across the southern half of our region. Sunshine and warmer temperatures return for the latter half of the work week before it turns unseasonably chilly heading into the weekend. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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10 PM Update... Winds have decoupled across the interior northern and western MA, but there are a lot of high clouds across the region and these clouds expected to stick around which will limit how cold it gets across NW MA. Not making changes to frost headlines but probably not getting any colder than 34-35 so any frost will be light and of limited duration. No changes to current forecast. Previous discussion... A strong ridge of high pressure anchored across Quebec will remain in control of our weather tonight. The low that has been meandering off the mid-Atlantic coast will push a bit further south tonight. This will allow some more low level dry air to work into southern New England and the pressure gradient to weaken just a bit. So while winds will diminish some tonight; they should still remain in the 20- 30 mph range along the coast and 30-40 mph across Nantucket. We will continue the Wind Advisory through 10 pm across Nantucket and Block Island as winds may continue to flirt with criteria for a few hours into this evening. Dry weather will persist tonight given the influence of Canadian High pressure. The question is how much partial clearing works in across the distant interior and are winds able to briefly decouple. The greatest risk for both of these to occur will be in northwest and north Central MA where we are expecting overnight lows to drop into the 30s. We will continue with our Frost Advisory for northwest MA. Later shifts may need to consider a southeast expansion, but winds may not be able to decouple enough given a good pressure gradient still in place. Therefore...expect the rest of the region to see overnight lows mainly in the upper 30s and 40s with the bulk of the lower clouds across eastern New England. But there will still be mid/high clouds around elsewhere based on model cross sections.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Monday... The ridge of high pressure to our northwest and the meandering wave of low pressure well to our south will continue to control our weather on Monday. We expect to see a mixture of sun & clouds, but certainly more sunshine that we experienced today given a drier low level push of air from the north. We still do expect an abundance of clouds across far southeast New England though give the NE low level flow. Dry weather will prevail across the entire region. High temps will remain below normal on Monday generally in the upper 50s to near 60; but a few spots could reach the lower 60s. The low level jet is weaker than today, but still supports 20 to 30 mph wind gusts with the strongest of those towards the southeast New England coast. Gusts up to 35 mph possible for Nantucket. Monday night... The guidance shows that this low off the mid-Atlantic coast does begin to slowly lift northward Monday night. This may allow for lower clouds to work northward later Monday night especially areas south of the MA turnpike. In fact...we may see a few showers work into our far southern zones toward daybreak Tuesday. Guidance differs on this potential, but greatest risk will be near the south coast, Cape and Islands. Low temps will mainly be in the upper 30s and 40s, but some middle or even lower 30s with frost are possible in parts of west/northwest MA if clouds remain to the south. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Highlights * Remnants of Ian linger to our south through Wednesday. Below normal temps and dry for most, with best chance of rain across southeast MA and southern RI. * Pick of the week weather Thursday into Friday, with plentiful sunshine and above normal temps in the 70s. * Strong cold front arrives Friday night into Saturday, with the first widespread frost/freeze possible Sat night. Temperatures moderate a little on Sunday but remain below normal. Details... Tuesday into Wednesday... Fairly benign weather overall for most with the first full week of October certainly bringing on a real fall feel. First half of the week, we are still dealing with the remnants of Ian or a secondary low that spins off Ian further to our south. The upper level pattern suggests that the remnants of Ian will not be in a hurry to exit into the Atlantic Ocean. The failure of the H5 low to get caught in the northern jet energy means it will meander across the Ohio valley/Appalachian. To the east, the Bermuda High will be strengthening, further blocking the exit route of Ian`s remnants or any secondary low that tries to spin off. Fortunately for those hoping for some dry weather to enjoy the foliage or outdoor activities, it does look like the bulk of the rain/overcast conditions will be to our south. Best chance for occasional showers or periods of rain will be across southeast MA and southern RI. Not out of the question rain showers could come up to the Mass Pike corridor. Certainly not a washout by any means, but much of the region will be in a prolonged cool northerly or northeasterly flow. So have kept PoPs rather probabilistic using blended guidance. So expect daytime highs to be about 5 to 10 deg below normal, except towards the CT valley which will be closer to normal. For reference, normal highs for the first week of October are in the mid 60s to near 70. NBM temps look reasonable for the most part. Given it is hard to pinpoint the northern extent of the clouds/rain, chose to stick largely to the NBM. It will also be quite breezy as well given the pressure gradient. But not anticipating the need for any land based wind headlines given the uncertainty of where the center of low pressure sets up and how quickly it exits. Thursday into Sunday... As the remnants of Ian and/or its spin off low finally exits, brief H5 ridging takes over New England so the latter half of the work week is looking spectacular. Temps warm back closer to normal if not at or slightly above normal. And the return of sunshine will make for very comfortable outdoor conditions during the day (mid 60s to low 70s) and cold nights (upper 30s to mid 40s). This is out ahead of a rather robust shortwave trough that looks to arrive overnight Friday into Saturday. There are still some questions how cold it gets, but models have trended with a latter arrival of the cold air mass, with 850mb temps falling to 0 to -3C and 925mb temps +2 to +4C, which is more typical of a late October air mass! In addition, given that forecast soundings show moist low levels, it is not out of the question we could see the season`s first snow flurries or showers across the Berkshires above 2500 ft, although better chances will be further north across northern New England given the colder temps and better jet dynamics. On a related note, there could be some showers accompanying the frontal passage, but it would be hit or miss in nature given that better jet dynamics are north of our area and the best chance for better shower coverage would be from the upslope component in the high terrain. So again not a given we can see snow at this time especially if it is a more progressive and drier frontal passage but this is a reminder that we are now into the part of the season where the high terrain can see snow from a climatology standpoint. Strong cold advection continues during the day on Saturday so highs are not expected to get out of the 40s across the high terrain and 50s elsewhere. Given the lingering 850-700mb moisture, should be quite a fair bit of stratocumulus and upslope showers. Drier air will also be advecting in with PWATs plummeting to less than 0.25 inches, which is near the minimum moving average according to the SPC sounding climatology for Chatham, MA! High pressure builds in and given mostly clear skies and depending on the extent to which boundary layer winds decouple Sat night, could see the region`s first widespread frost/freeze. Given the moderate confidence on how efficient the radiational setup is 6 days out, largely stuck to blended guidance. Temperatures moderate a little on Sunday, but remaining below normal. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 2340Z TAF Update... Tonight...High Confidence. Lingering MVFR cigs across the Cape/Islands should improve to VFR by early evening although this process may be a bit slower across Nantucket. We also may see some marginal MVFR ceilings try to develop again towards daybreak near the southeast New England coast. Otherwise...VFR conditions will continue. NE wind gusts of 25 to 35 knots along the coast will diminish to between 20 and 30 knots tonight; but gusts up to 35 knots will remain possible across Nantucket. Monday...High confidence. Mainly VFR, but can not rule out some brief marginal MVFR ceilings flirting with the southeast New England at times. NE wind gusts of 20 to 30 knots along the coastal plain and up to 35 knots across Nantucket. Monday night...High Confidence. Mainly VFR, but some MVFR ceilings may develop especially near daybreak Tuesday across the southeast New England coast. NE wind gusts of 15 to 25 knots towards the Cape and Islands and up to 30 knots for Nantucket. KBOS Terminal...High Confidence in TAF. KBDL Terminal...High Confidence in TAF. Outlook /Tuesday through Friday/... Tuesday: Mainly VFR, with local MVFR possible. Windy with areas of gusts up to 35 kt. Slight chance SHRA. Tuesday Night through Wednesday: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA. Wednesday Night: VFR. Breezy. Thursday through Thursday Night: VFR. Friday: VFR. Breezy. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Tonight through Monday night...High Confidence. The overall pattern with high pressure to our north and a wave of low pressure well to our south will continue through Monday night. The low level jet will diminish a bit tonight, but still expect modest NE wind gusts to continue right through Monday night. Overall...expect NE wind gusts of 25 to 35 knots with 7 to 12 foot seas persisting through Monday night. The higher of these winds and seas will be across our southern waters; where the gradient is the strongest. While we will gradually be able to transition Gales to small craft headlines as the night wears along across many of our waters; we will need to continue Gales right through Monday night across our southern outer-waters. Outlook /Tuesday through Friday/... Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. Chance of rain showers. Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Chance of rain showers. Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 9 ft. Chance of rain showers, isolated thunderstorms. Wednesday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers. Thursday: Winds less than 25 kt. Seas up to 5 ft. Thursday Night through Friday: Winds less than 25 kt. Seas locally approaching 5 ft. && .TIDES/COASTAL FLOODING... Coastal flood advisory has been allowed to expire for Nantucket for the high tide that happened around 6 PM. Preliminary obs shows a storm surge of around 1.1 ft with a peak water level of 4.93 ft. Given the 30-35 kt wind gusts out of the northeast, the main concern was minor splash over. Do not expect any coastal flooding issues further north as the expected surge here will be less, generally 0.5 to 1 foot, and seas not high enough to produce flooding. However, some minor beach erosion is possible for the next few days given persistent onshore flow. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...Frost Advisory from 1 AM to 8 AM EDT Monday for MAZ002-003-008. Wind Advisory until 10 PM EDT this evening for MAZ024. RI...Wind Advisory until 10 PM EDT this evening for RIZ008. MARINE...Small Craft Advisory until noon EDT Monday for ANZ230-236. Gale Warning until 2 AM EDT Monday for ANZ231-250-251. Gale Warning until 5 AM EDT Monday for ANZ232>234. Gale Warning until 8 AM EDT Monday for ANZ235-237. Gale Warning until 8 AM EDT Tuesday for ANZ254>256.
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&& $$ SYNOPSIS...Frank/Chai NEAR TERM...KJC/Frank SHORT TERM...Frank LONG TERM...Chai AVIATION...Frank/Chai MARINE...Frank/Chai TIDES/COASTAL FLOODING...

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