Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 231925 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 325 PM EDT Sat Mar 23 2024 .SYNOPSIS...
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Heavy rain today, exiting by midnight. Drying out Sunday into early next week but rather windy along the coast, especially Cape and Islands.Cooler with breezy to gusty northeast winds Monday and Tuesday, and chances for light rain showers expanding westward from the offshore waters. Building rough seas are likely Monday and Tuesday over the southeastern waters. It remains unsettled through mid to late in the week, with rain chances returning Wednesday night into Thursday, and a better chance around late Thursday and into Friday. Temperatures trend above normal for mid to late in the week.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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The low bringing us all this rain is currently centered over the Delmarva, poised to lift into our offshore waters and slide along the south coast then over the Cape Cod canal this evening and overnight. The excessive rainfall is the result of a strengthening low level jet coinciding with moist inflow off the Atlantic combined with large scale ascent thanks to placement beneath the entrance region of a 150 kt upper jet. This sets up a good pattern for heavy rainfall, with HREF guidance indicating the period of heaviest rain being generally 4pm-10pm with potential for as much as 1-2 inches in 3 hours for a brief period from coastal CT to RI to southeast MA. The Flood Watch remains in effect for some river flooding and the potential for urban/poor drainage flooding as well. The previously mentioned low level jet kicks in in earnest this evening with gusts to 40-50 mph. The cold front then drops through and colder air filters in on the back end. However, dry air also quickly moves in, so any changeover back to snow should be very brief with little to no impact. Rain comes to an end from west to east between 10pm and 2am. Winds quickly shift to the northwest and remain gusty overnight, gusting 25 to 35 mph.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/...
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Sunday will be dry but blustery thanks to our placement between a strong low well south over the Atlantic and high pressure over the Great Lakes. This also produces winds out of the northeast which will serve to keep moisture (clouds) over eastern MA, potentially into RI and even eastern CT tomorrow. Further west expect even more sun. Winds gusting 25 to 35 mph will make highs in the upper 30s feel more like upper 20s/low 30s. The gradient only tightens overnight as the storm passes closer to SNE and this will mean deteriorating conditions on our southern and eastern waters with wind gusts to 35 to 45 kts and seas of 12-14 ft.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/...
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Highlights: * Temps near or slightly cooler than normal Mon and Tue, with northeast breezes/gusts. Light showers offshore expanding westward Mon night/Tue? * Likely very choppy, rough seas over southeast waters Mon and Tue. * Remains unsettled mid to late week with chances for rain Wed night/Thu and a better chance Thu night/Fri. Temps trend near/above normal. Details: Monday and Tuesday: Rather prolonged period of onshore NE flow, with a tightening pressure gradient driven by a 1040 mb high pressure area over northeast Quebec and a nearly vertically-stacked but strong coastal low over 35N/68W lat/lon vicinity. Sfc ridge axis from the high is expected to extend southward through the mid-Atlantic states and Carolinas, though it tends to weaken as we move through time. With that said, there remains considerable disparity on when this ridge axis starts to weaken, which would influence the northward return of showers and how far west any showers may extend. The tightening NE pressure gradient will bring stiff NE winds to eastern and especially southeastern portions of Southern New England. NE gusts around 35 to 45 mph take place over eastern and southeast MA and RI and around 20-30 mph inland. Though this wind will bring a bit of chill, the persistent NE gradient and stable fetch region seem more likely to bring some impact for marine and coastal interests, with building seas and winds gusting to gale force. Rough, choppy seas building to 12-14 ft are expected and though it`s not beach season, could be some surf/beach erosion issues along east-facing shorelines, especially Cape and Islands. With the stated uncertainty in how any offshore moisture/related showers expands landward and further inland, kept PoP lower than the high-chance NBM values; GFS would favor a shutout entirely, although some consensus in the GEM/ECMWF in showing westward-spreading and light rain showers Mon aftn along the coast, then further inland into Tue/Tue night. PoPs will need adjusting, either up or down, as we move through time, but rain amts look light and wouldn`t be necessarily impactful. Despite slowly rising 925-850 mb temps, a limited mixing depth and more clouds further south and east will likely favor slightly below normal high temps and slightly above normal low temps for each day. Overall a pretty chilly, raw couple days are likely with the NE breezes, especially nearest the coast. Wednesday through Friday Night: Ridging aloft between the distant/offshore coastal low and a broad upper trough over the east-central CONUS weakens considerably early Wed. The broad trough gradually shifts eastward and sends a couple periods of rain showers to our area. One focused period looks to take place Wed night/early Thurs as a cool front moves east. Then a somewhat better chance later Thurs into Fri as the cool front stalls offshore and induces low pressure near the Carolinas to move NNE into the mid-Atlantic and coastal New England. PoPs were highest in this latter period in the 45-60 percent range, higher east. Still uncertain in some of the details and how quickly rain would shift eastward/offshore, but the mid to late week period looks pretty unsettled. Temps trend near to above normal, with highs in the upper 40s/low 50s and lows in the mid/upper 30s.
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&& .AVIATION /19Z SATURDAY THROUGH THURSDAY/...
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Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High- greater than 60 percent. 18Z update... This afternoon...High confidence in trends. Rain will pick up in intensity after 20Z across CT then heavy rain spreads NE into RI and portions of central and eastern MA this evening. Southeast winds gradually increase throughout the day ranging from 10 kt across the interior to 15 to 20 kt over the coastal plain. A strong low level jet will likely increase winds across Rhode Island and southeast MA between 21z and 03z, gusting as high as 35 to 40 knots. Tonight...High confidence in trends. Moderate in timing. IFR/MVFR cigs improve to VFR returns as precip gradually ends from west to east from 02Z to 09Z. Rain lingers a bit longer over The Cape/Island terminals likely tapering off between 04 and 07Z with VFR returning. Winds strengthen after 00Z behind a surface cold front. 15 to 25 knot sustained northwest winds with gusts up to 35 knots. Sunday...High confidence. VFR. Strong winds with local gusts up to 40 kt. Sunday night...High confidence. VFR. Northeast winds 15 to 20kts, gusting to 30 kts just offshore. KBOS TAF...RA becoming heavy this afternoon with IFR conditions. Rain ends late this evening around 04z. Gusty southeast winds as well, nearing 30 knot gusts around 00z through 02Z/03Z. Shift from southeast wind to northerly wind by 03z tomorrow with improving CIGS to MVFR. KBDL TAF...Rain for the rest of today with IFR to LIFR conditions. Rain becomes heavy this afternoon and through this evening, ending after 00z. Light northeast wind will become northerly after 00Z and gusting 20 to 25 knots, and improving CIGS to MVFR. Outlook /Monday through Thursday/... Monday: VFR. Strong winds with local gusts up to 40 kt. Monday Night: Mainly VFR, with local MVFR possible. Strong winds with local gusts up to 40 kt. Tuesday: Mainly VFR, with local IFR possible. Windy with gusts up to 35 kt. Tuesday Night: Windy with areas of gusts up to 30 kt. Chance RA. Wednesday through Wednesday Night: Chance RA. Thursday: Breezy. Chance RA.
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&& .MARINE...
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Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. * Gale Warning in effect for all waters Saturday and continues into Sunday Tonight: A cold front moves over the waters tonight. Winds become even stronger out of the north/northwest with 30 knot sustained winds for most of the marine zones. Wind gusts from 30 to 40 knots. Seas increase to 10 to 13 feet over the outer coastal waters, and 6 to 10 feet for the nearshore waters. Sunday: Low pressure system to our north will continue northerly gales with gusts to 40 knots. Seas on the outer waters are greater than 12 feet, near shore waves are 6 to 10 feet. Sunday night: Low pressure passing to our south will increase gusts and seas. NE winds 20-35 kts gusting 35 to 40 kts with seas increasing to 12-14 ft. Outlook /Monday through Thursday/... Monday: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 15 ft. Slight chance of rain. Monday Night: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 14 ft. Slight chance of rain. Tuesday: Low risk for gale force winds with gusts up to 40 kt. Rough seas up to 14 ft. Slight chance of rain. Tuesday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 12 ft. Slight chance of rain. Wednesday: Winds less than 25 kt. Rough seas up to 9 ft. Chance of rain. Wednesday Night: Winds less than 25 kt. Areas of rough seas. Chance of rain. Thursday: Winds less than 25 kt. Seas up to 5 ft. Rain likely.
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&& .TIDES/COASTAL FLOODING...
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There is some concern for Narragansett Bay during the high tide this evening but confidence has grown that th core of the jet stays just to the east and so the surge will likely be limited to 1.5-2 ft which will keep water levels below flood. A Coastal Flood Statement is in effect. The worst case scenario is for pockets of minor flooding.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...Flood Watch through Sunday morning for CTZ002>004. MA...Flood Watch through Sunday morning for MAZ005>007-009-011>024. Wind Advisory until 11 PM EDT this evening for MAZ017>024. RI...Flood Watch through Sunday morning for RIZ001>008. Wind Advisory until 11 PM EDT this evening for RIZ004>008. MARINE...Gale Warning until 2 PM EDT Sunday for ANZ230>235-237-251. Gale Warning until 2 AM EDT Sunday for ANZ236. Gale Warning until 8 PM EDT Sunday for ANZ250-254>256.
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&& $$ SYNOPSIS...Loconto/BW NEAR TERM...BW SHORT TERM...BW LONG TERM...Loconto AVIATION...Loconto/BW MARINE... TIDES/COASTAL FLOODING...KJC

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