Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 220314 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1114 PM EDT TUE JUN 21 2016 .SYNOPSIS... Seasonable temperatures are expected for tomorrow with a few showers possible. Low pressure passes just south of New England Thursday, bringing showers and cooler temperatures followed by dry and seasonable conditions Friday. Dry and very warm weather this weekend into early next week away from the coast, with a chance of showers/t- storms next Tue ahead of a cold front. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
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1045 PM Update... While the cold front ever so slowly shifts S this evening, scattered showers developed from the far northern fringe of convection that moved off the N NJ coast. These showers have tracked across the southern waters, including the south shore of the lower and mid Cape, Nantucket and Martha`s Vineyard over the last few hours. Lightning has remained well S of the Islands, though have noted a couple of C/G strokes well E of Nantucket since 02Z. Also noting light patchy fog across the outer Cape and Nantucket, as well as some haze that was reported early this evening by the Nantucket and Vineyard ferry boats. Expect continued low temp/dewpt spreads across the Cape and Islands, so should see low clouds and fog develop overnight. May see some fog also develop around or after 08Z along S coastal areas, but should be brief there. Elsewhere, will see mainly clear skies with diminishing winds as a weak ridge crosses. Have adjusted temps along the S coast a bit with the low temp/dewpt spreads, otherwise appears they are in good shape. Have updated the near term forecast to bring conditions current. Previous discussion... The front will be slow to move offshore with a slow decrease in dewpoints over Cape Cod and especially the islands. As the boundary layer cools, this will set up favorable conditions for areas of fog to develop over the south coastal waters and the adjacent islands. Otherwise, expect a pleasant night with comfortably dry air and diminishing winds which will allow low temps to drop into the 50s most locations. The low dewpoints should preclude fog development outside of the islands.
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&& .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
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WEDNESDAY... Very potent shortwave will move through the region. This wave combined with cold pool aloft will yield to diurnal showers. Highest coverage will be across route 2, which is closer to the better dynamics, with more scattered showers north of the Mass Pike. Some instability will develop which could trigger a few isolated thunderstorms, but the better chance will be north of the region where the temps aloft are cooler. Shortwave will already be moving out of the region by 18z so any precip will be confined to the morning to early afternoon hours. Appears a pleasant afternoon is on tap for the region with clearing skies and temps warming into the mid to upper 70s. A few spots reaching into the 80s. Dewpoints will remain in the mid 40s to low 50s, very comfortable! WEDNESDAY NIGHT... Weak ridging will build into the region as heights aloft rise. Anticipate a mostly dry night with high level clouds overspreading ahead of the next weather system. Temperatures will remain in the low to mid 50s.
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&& .LONG TERM /THURSDAY THROUGH TUESDAY/...
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Highlights... * Showers likely Thu with below normal temps * Dry and seasonably warm Fri * Much warmer this weekend into early next week with 90+ degree temps possible Sun/Mon in the interior * More humid with chance of showers/t-storms next Tue Overview... Model guidance in good agreement on the overall pattern in the extended period with longwave trof over the NE lifting NE as expansive ridge over southern CONUS builds north across Gt lakes and into New Eng this weekend into early next week. A frontal wave to the south will likely bring a period of showers to SNE Thu, then mainly dry with a notable warming trend this weekend into early next week with 90+ degree heat possible interior. Next upstream trof approaching next Tue will bring a threat of showers/t-storms. Details... Thursday... Frontal wave approaches on Thu with consensus of the guidance keeping the warm front and sfc low south of New Eng. We discounted the NAM which is too deep and too far N with low pres with unrealistically strong low level jet. It should start out dry early Thu, then showers will overspread the region as deep moisture plume and mid level lift move in. Best instability, higher theta-e air and low level jet will remain to the south where best chance of t-storms and locally heavy rainfall. However, there is some elevated instability just south of New England so can`t rule out an isold t- storm near the south coast. GFS is a bit more robust with QPF than ECMWF. We used a blend which gives potential for 0.25-0.50" rainfall. With showers moving in and E/NE flow north of the boundary, temps will be below normal with highs upper 60s to lower 70s. Friday through Monday... High pres builds in with dry weather and a warming trend. Seasonable temps Fri with coastal seabreezes, then warming temps this weekend into early next week, especially interior away from potential seabreezes. Warmest days will likely be Sun/Mon with 90+ degree temps possible in the interior valleys. Warmer ECMWF has 18-19C at 850 mb which would translate to mid 90s. GFS not as hot. Southerly flow will hold temps in the 70s along the immediate south coast. Dewpoints mostly in the 50s so humidity levels will be low. Tuesday... Another very warm day with temps well into the 80s while ECMWF shows potential for more 90+ degree heat. Dewpoints will be increasing into the 60s ahead of a cold front which will help to destabilize environment so increasing threat of showers/t-storms but this will be dependent on the timing of the approaching front.
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&& .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
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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 Wednesday Night/... Overnight...High Confidence. VFR through the period. IFR CIGS/VSBYS in low stratus/fog likely developing over the outer Cape and KACK. Wednesday...Moderate Confidence. Scattered showers during the first half of the day with a low risk for thunder. Mainly VFR conditions through the period. Wednesday night...High Confidence. VFR. KBOS TAF...High confidence. VFR. Low risk for -TSRA early Wed afternoon. KBDL TAF...High confidence. VFR. Outlook /Thursday through Sunday/... Thursday...Moderate confidence. Conditions lowering to MVFR with showers developing and low risk for t-storms near the south coast. Friday through Sunday...High confidence. VFR. Sea breezes likely.
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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. Short Term /through Wednesday Night/...High confidence. Weak cold front will push through the waters tonight switching the winds to a more westerly directions. Seas and winds will relax this evening and into tonight so have dropped SCA. Showers and isold thunder possible across the eastern waters Wednesday afternoon. Otherwise building southerly swell on Wednesday will result in seas reaching 5-6 feet. Issued a SCA for seas where confidence was highest that this would occur. Seas will begin to relax by Wednesday night. Outlook /Thursday through Sunday/... Thursday...Moderate confidence. SW Winds becoming easterly with speeds less than 20 kt. Seas may approach 5 ft over southern waters. Friday...Moderate Confidence. North winds becoming locally onshore over nearshore waters as seabreezes develop. Lingering 5 ft swell possible southern waters. Saturday and Sunday...Moderate confidence. Light winds becoming onshore each day over nearshore waters as seabreezes develop. Seas below SCA.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas from 8 AM Wednesday to 8 AM EDT Thursday for ANZ255-256. && $$ SYNOPSIS...KJC/Dunten NEAR TERM...KJC/EVT SHORT TERM...Dunten LONG TERM...KJC AVIATION...KJC/Dunten/EVT MARINE...KJC/Dunten/EVT

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