Area Forecast Discussion
Issued by NWS Boston, MA

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687 FXUS61 KBOX 240825 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 424 AM EDT TUE MAY 24 2016 .SYNOPSIS...
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Scattered showers and few embedded thunderstorms this morning will focus themselves primarily across Western MA and Northern CT by afternoon. An upper level ridge of high pressure will then bring very warm to borderline hot weather to most of the region Wednesday through Saturday, except for times of cooler temperatures on the immediate coast. A few showers and thunderstorms are possible Thursday night into Friday, but a better chance exists Saturday afternoon and evening ahead of the cold front.
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&& .NEAR TERM /UNTIL 6 AM THIS MORNING/... 1110 PM update... Light showers rotating westward around cutoff H5 low pressure near or just off the mid Atlc coast reaching the S coast of RI into N central and NE CT at 03Z. Looks like most of the activity will remain W of E MA and more of RI, but can not rule out widely sct showers pretty much across the remainder of the region into the early morning hours. Then, toward sunrise, will start to see sct showers pretty much anywhere as weak short wave rotates westward in the cyclonic upper flow to the south, as well as decreasing temp/dewpoint spreads especially near the coast. With the onshore wind, will see low clouds and patchy fog moving in. Would not be surprised to see some spotty drizzle as well. 18Z GFS and new 00Z NAM both continue to signal increasing instability, with total totals up to the lower 50s, surface based LIs down to zero to -2 and K indices to the lower 30s around or after 09Z. NAM appears too robust considering the lack of convection into the region, so used a blend of the GFS/NAM with a bit more weight to the GFS. Noting some CG and in cloud lightning S of 40N late tonight, but appears this will rotate S of the region for now. Have kept mention of thunder in the forecast toward daybreak into Tuesday morning, though went with isolated wording. Remainder of forecast in pretty good shape, but have updated to bring conditions current. Previous discussion... Low pressure wobbles N evolving into its dying phase undergoing occlusion. During this morphology, focus is on the crux of mid- level vortmax energy and parent weak low-level convergence rounding W-NW round the low into S coastal New England. Should see decent low to mid level forcing with some venting aloft, along the leading edge of which a band of light to moderate rain should emerge. Also isolated thunderstorms are possible given marginal instability and weak shear parent to expected lift, but such activity should be non severe with the main threats being lightning and locally heavy rain. A consensus of high-res and mos-guidance performed, confidence is for a band of activity to pivot NW across S New England settling N to S across W New England and along the high terrain. This keeps a good chunk of E/SE MA in chance PoPs. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 AM WEDNESDAY/... Tuesday... Breaking down. Low chokes itself off entraining drier air as it stacks and undergoes occlusion within its dying phase. The trowaling and comma shape to the low persists albeit weaker seemingly over W portions of New England parent with low level convergent flow along the E slopes of high terrain and forcing per rotating mid-level vortex energy. But to the E we could see some improvement with clouds becoming broken and perhaps some hints of sunshine. Thus can not rule out partial clearing. PoPs evolving with highest confidence over the Berkshires while chance-scattered to the E/SE if forecast models are right in the evolution of drier air wrapping into the system. A lot of wiggle room and wobble with this system to which the high-res guidance is not absolutely succinct but has a decent handle on the trend. Will avoid high PoPs accordingly with the scattered to broken nature of the low. Thunder does remain a possibility with continued marginal instability and weak shear. Think isolated chances and will prevail accordingly. Cooler day with clouds in abundance and E/NE flow. Highs up into the 60s. An edge warmer to the W as conditions improve late in the day with winds shifting out of the W/NW. Tuesday Night... The end. Low continues to undergo its dying phase choking upon drier air as it peels off to the E. Comma head over the W sweeps E across S New England per a consensus of high-res forecast trends, but by this point the activity is all but scattered. Should see most of the wet weather by consensus conclude by midnight behind which W/NW flow prevails. Anticipated clearing and light winds, would expect lows to drop into the 40s, and considering the recent rains, can not rule out some dense fog development if conditions are right. && .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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Highlights... * Very warm Wed/Thu/Fri with highs well up into the 80s except cooler immediate coast at times * Hot Saturday afternoon w/highs mainly upper 80s to the lower 90s * A few showers/t-storms possible Thu night/Fri but best chance Sat afternoon/evening ahead of cold front * Turning much cooler Sun and especially Mon along the coast Details... Wednesday...Closed upper level low lifts northeast of our region allowing for rising heights/warmer mid level temps. More importantly, surface winds will turn to the west which makes a huge difference in afternoon high temps this time of year. Given 850T between 13c/14c and plenty of late May sunshine, high temps should be in the mid to upper 80s for most including Boston, as any sea breezes that develop along the Eastern MA coast will be overcome by increasing gradient by afternoon. It will be a bit cooler on the south coast/Cape/Islands, but still should see highs well into the 70s to near 80. Dry weather will dominate Wednesday, but there is a low risk of a spot shower/t-storm during the afternoon/early evening across the interior. Limiting factors though will be dry mid levels and lack of low level forcing. Wednesday night...Other than a low risk for a spot shower/t-storm across the interior during the evening dry weather is expected behind a weak cold front. Low temps will only fall back into the 50s in most locations with 60 to 65 in some of the urban centers. A touch of patchy fog may develop in the typically prone locations toward daybreak. Thursday...Upper level ridging across the Southeast U.S. continues to nose into southern New England. This will result in plenty of sunshine and with warm mid level temps, highs again should reach well into the 80s in most locations. However, gradient will be weaker allowing for sea breezes to develop on the immediate Eastern MA coast including Boston by early afternoon. High temps will still likely reach well up into the 70s to near 80 in this region before sea breezes develop and temps fall a bit. Should remain dry given lack of forcing and upper level ridging nosing into this region. Thursday night and Friday...A shortwave will lift northeast into northern New England Thu night/Fri. While the best forcing will to our north, a few showers/t-storms are possible with the best chance across western and northern MA. Certainly not expecting a washout though and the majority of the Thu night/Fri will be dry. Still looks like a warm afternoon with temps into the 80s, but it may be cooler across Northeast MA depending on location of backdoor cold front. Saturday...A hot day with westerly flow and 850T near 16c. This should yield highs in the upper 80s to lower 90s for most locations. Dewpoints into the 60s will make it feel somewhat muggy. Pre-frontal trough ahead of an approaching cold front may trigger scattered showers/thunderstorms mainly Saturday afternoon and evening. Sunday and Monday...High pressure over the Canadian Maritimes will build south into New England. So despite rather high height fields, northeast low level flow will result in much cooler temps Sun and especially Mon particularly along the coast.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tonight/... Overnight...Moderate Confidence. Mainly VFR through 04Z-06Z, except LIFR CIGS/MVFR-IFR VSBYS moving onshore from Cape Cod to along E coastal Mass. Should see MVFR- IFR CIGS/MVFR VSBYS move W to about KORH-KIJD with spotty MVFR CIGS/VSBYS across the CT valley mainly after 06Z. Scattered showers with MVFR conditions across N CT/W RI into CT valley. Isolated thunder possible after 08Z mainly near S coast. Light E-NE winds. Tuesday...Moderate Confidence. SHRA and chance TSRA continue with greatest confidence over W terminals. Widespread MVFR/IFR impacts begin to shift E with the usherance of winds backing out of the W/NW. Gusts of around 15 kts possible. Tuesday Night...Moderate confidence. Continued clearing trend W to E with W/NW winds. Improving to VFR. It is perhaps at the start of the period that MVFR/IFR will only linger along the E coast of MA. KBOS TAF...Sct showers will move across the terminal tonight and into tomorrow. Low prob for some thunder. VFR will drop to MVFR/IFR after 06z. KBDL TAF...Confident the terminal will see a fair share of -RA beginning around midnight and continuing through much of Tuesday before clearing out late. Moderate prob for TSRA. MVFR conditions after 06z. Outlook /Wednesday through Saturday/... Wednesday and Thursday...High confidence. VFR conditions other than a few hours of patchy ground fog possible toward daybreak Thu in the typically prone locations. Thursday night and Friday...Moderate confidence. VFR conditions likely dominate but some brief MVFR conditions possible in a few showers/t-storms mainly across the interior. Saturday...Moderate confidence. Mainly VFR conditions but brief MVFR- IFR conditions possible Saturday afternoon/evening in scattered showers and thunderstorms.
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&& .MARINE...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Overnight and Tuesday...Moderate Confidence. E-NE winds with gusts up to 15 kt mainly overnight, then diminishing Tuesday. Seas 4 feet or less. Visibility reductions in areas of fog moving W from Mass Bay and E of Cape Cod overnight, local mist as well. Scattered showers along the S coast of RI, then continue to develop across entire S coast, possibly reaching to E coastal areas by daybreak. Isolated thunderstorms after 08Z through mid morning Tuesday possible. Tuesday Night...Moderate Confidence. Winds back out of the W/NW with departure of the low. Change in wind direction against a E/SE swell, could see some wave heights up to 5 feet on the outer waters requiring small craft advisories. Aside, rain comes to an end and visibilities improve if they had not done so during the day Tuesday. Outlook /Wednesday through Saturday/...High Confidence. Winds and seas will remain below Small Craft Advisory thresholds the majority of the period with the exception being Wednesday night. Some brief near shore southwest wind gusts of 20 to 25 knots are likely Wed afternoon...which will result in some choppy seas. In addition, long southwest fetch may bring a period of 5 foot seas across our southern waters Wednesday night which may require headlines.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas from 1 PM this afternoon to 4 AM EDT Wednesday for ANZ254-255. Small Craft Advisory for hazardous seas from 3 PM this afternoon to 1 AM EDT Wednesday for ANZ256.
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&& $$ SYNOPSIS...Frank NEAR TERM...Dunten/EVT SHORT TERM...Sipprell LONG TERM...Frank AVIATION...Frank/Sipprell/EVT MARINE...Frank/Sipprell/EVT

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