Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 241909 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 309 PM EDT Sat Jun 24 2017 .SYNOPSIS...
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Weak high pressure brings mostly clear skies and light winds tonight, as well as lower humidity. A fast moving disturbance moves across New York and Northern New England late Sunday, bringing scattered showers to northern parts of our area. A warming trend begins for the latter half of the week with a return to summer heat and humidity by Friday.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Weak high pressure builds over the northeast tonight, coincident with a shortwave ridge racing through the upper flow. Expect most of the clouds to diminish overnight. The diminishing pressure gradient will bring lighter wind. This opens the potential for some radiational cooling overnight. With dew points falling into the 50s, expect the cooler locations away from the cities to reach the low to mid 50s overnight, while the rest of us have mins in the upper 50s and lower 60s.
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&& .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/...
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Broad cyclonic flow across the northern USA, but with a strong 120-knot jet moving through the flow and driving features quickly through the flow. Shortwave over the Great Lakes Sunday morning races northeast, crossing Upstate NY in the afternoon and Northern New England Sunday night. This shortwave will carry enough cold air at 500 mb to destabilize the airmass across these areas Sunday. The instability parameters are consistant with this, and favor thunder to our north and west but not in Southern New England. Even so, we will be in the right entrance region of the upper jet, which will favor upper venting and generate some lift. We will forecast a chance of afternoon/evening showers, primarily across Western and Central Mass. The mixed layer is forecast to reach to at least 800 mb and possibly 750 mb. Winds in layer will be 15-20 knots, so expect southwest winds gusting to those speeds in the afternoon. Temperatures at 800 mb will be 7-9C, equiv to 12-14C at 850 mb. This would suggest max sfc temps in the low to mid 80s. After the shortwave passes to our north, any showers should diminish. For most folks, it should be a fair night with temps in the 50s.
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&& .LONG TERM /MONDAY THROUGH SATURDAY/...
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Highlights... * Cooler with a few showers/isold t-storm possible Mon into Wed * Warming trend toward end of the week with return to summer heat/humidity by Fri Details... Monday into Wednesday... Anomalous mid level trof moves eastward from the Gt Lakes Mon pushing into New Eng late Tue and may linger into early Wed. Temps continue to cool aloft Mon which may trigger a few showers or This afternoon and tonight... Showers and thunderstorms over the waters will trend northeast and move east of the waters during the early afternoon. Expect south winds to shift out of the west at that time. Winds will then diminish at that time. Waves of 5 to 7 feet will linger early afternoon on the outer waters and the Rhode Island waters, then subside towards Sunday morning. All other waters should remain below 5 feet.an isold t-storm in the interior, but best chance of showers/t-storms will likely be on Tue as the trof approaches and core of coldest air aloft moves overhead. Timing of when the trof exits is somewhat uncertain but GFS and ECMWF still have -21C at 500 mb 12z Wed before temps aloft warm in the afternoon. So expect isold showers and t-storms again on Wed with focus more across eastern half New Eng. Temps through Wed will average near or slightly below normal with highs mainly 75-80 and lows in the 50s. Thursday and Friday... Pattern change signaled as upper trof moves out with rising heights and zonal flow across New Eng. This will result in a warming trend with temps into the 80s Thu and possibly 90+ on Fri. Humidity levels should still be comfortable Thu as dry air remains in the lower levels, but higher dewpoints will be moving in by Fri. Mainly dry weather, but developing warm advection may bring a few showers Thu afternoon to northern areas, then chance of afternoon showers/t- storms Fri as atmosphere destabilizes.
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&& .AVIATION /18Z SATURDAY THROUGH THURSDAY/...
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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 Sunday Night/...Moderate-High confidence. Tonight... VFR. Mostly clear skies with diminishing wind, becoming calm in the interior. Sunday... VFR. Increasing cumulus clouds late morning and afternoon especially northwest of I-95. Scattered afternoon showers ORH- HFD-BAF and points north. Could be brief MVFR cigs/vsbys in any afternoon shower. Sunday night... VFR. West winds. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Monday through Thursday/... High confidence. Mainly VFR. A few diurnally driven showers and perhaps an isold t-storm each day.
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&& .MARINE...
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Tonight... West winds become gusty from the northwest early and then diminish overnight as high pressure builds over the waters. The high will bring drier air. Rough seas linger on the outer waters and on RI Sound and Block Island South with 5-7 foot heights this evening, then diminish overnight. Small Craft Advisory will linger on the RI waters this evening, and they will continue on the outer waters overnight. Sunday and Sunday night... Winds become south-southwest as the high pressure moves off to the east. Afternoon winds should remain 20 knots or less. Rough seas linger during the morning on the southern outer waters and possibly parts of RI Sound, but will trend below 5 feet by mid afternoon. Winds and seas remain below Small Craft thresholds Sunday night. Outlook /Monday through Thursday/... Sunday...High confidence. Some lingering 5 ft seas possible over the southern waters, otherwise winds will remain below SCA. Monday through Wednesday...High confidence. Quiet boating weather with winds and seas below SCA. A few hours of nearshore lower 20 knot wind gusts are possible each afternoon.
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&& .TIDES/COASTAL FLOODING...
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Astronomical tides are rather high through this weekend during the night time cycles. Boston has a 12.4 ft high tide forecast around midnight tonight and 12.2 ft just after midnight Sunday night. While most places had their highest astronomical tide of the year last month, a few spots along our coast will have it with this June set of highest tides. Either way, the difference between the May and June highest tides is small. While offshore winds are forecast, current conditions suggest a 0.4 surge which will result in minor splashover. Thus will continue a coastal flood statement for tonight`s high tide.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...High Surf Advisory until 8 PM EDT this evening for MAZ020-023- 024. RI...High Surf Advisory until 8 PM EDT this evening for RIZ006>008. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ231>234. Small Craft Advisory until 11 AM EDT Sunday for ANZ235-237. Small Craft Advisory until 2 AM EDT Sunday for ANZ250. Small Craft Advisory until 8 PM EDT Sunday for ANZ254>256.
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&& $$ SYNOPSIS...WTB/KJC NEAR TERM...WTB SHORT TERM...WTB/Sipprell LONG TERM...KJC AVIATION...WTB/KJC MARINE...WTB/KJC TIDES/COASTAL FLOODING...

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