Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 270920 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 520 AM EDT WED JUL 27 2016 .SYNOPSIS...
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High pressure will bring dry but continued hot conditions through Thursday. A cold front will slowly drop south across southern New England Thursday night, then stall across the region Friday. Low pressure will push off the south coast Friday into Friday evening, bringing the chance for showers and thunderstorms. Showers may linger this weekend, with a few thunderstorms possible Sunday. Conditions will improve early next week as high pressure slowly moves in from the northwest.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/... High pressure builds overhead bringing sunny skies and light shifting wind. The solar heating will allow temperatures to climb quickly during the day, and the light wind will allow sea breezes to develop along the coasts around midday. The heating will build the mixed layer to at least 800 mb and possibly a little higher. Forecast temperatures at that height would be equivalent to 18-19C at 850 mb. So expect max surface temps in the low to mid 90s, buffered a little at the shoreline by the sea breeze. No change to humidity levels. Heat index values in the low 90s. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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Tonight... High pressure moves offshore but maintains fair skies and light wind. Light south winds possible by morning, but advection of higher dew points limited. Expect similar min temps, mainly in the upper 50s and 60s. The light flow may also allow some patchy fog in the valleys. Thursday... High pressure offshore with south to southwest winds over New England. Fair skies will again allow deep mixing. RH fields below 850 mb remain dry while some moisture increase at 800 mb would allow increasing clouds during the afternoon. Temperatures in the mixed layer are equiv to 19C at 850 mb, so low to mid 90s again looks reasonable. Depending on the strength of surface winds, there may be another buffering sea breeze along the eastern MA shore for part of the afternoon. But confidence in a persistent sea breeze is low at this time. This leaves the question of precip. Moisture and instability is initially focused on Northern New England but could slip south into Northern/Western MA late afternoon/evening. Models do show a surface front moving south into our area, but also show moisture and favorable jet dynamics remaining in Northern New England. Plenty of dry air below 850 mb to interfere with showers. We will show chance pops moving into Northern/Western MA starting 21Z, with slight chance into Northern CT.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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Highlights... * Temperatures near seasonal levels into early next week, then warming again by Tuesday * Low pressure wave looks to pass near or south of the region Friday and Friday night, which may bring steady rainfall along with scattered thunderstorms * Spotty showers/thunderstorms through the weekend as front lingers * High pressure builds slowly south out of Quebec early next week Overview and model preferences... Medium range models continue to show digging H5 trough across the Great Lakes region while a surface front slowly works S out of northern New England Thu night/Friday. As the H5 flow backs to SW, the front will tend to stall across the region. Looks like best shot for steady rainfall as well as convection during Friday/Friday night. The H5 trough will slowly shift E during this weekend. The cold front will slip S of the region Saturday with mainly dry conditions. However, may see another wave move off the south coast during Sunday with the chance for scattered showers, with some thunderstorms possible near and S of the Mass Pike as well as the E slopes of the Berkshires. Lower confidence with this feature as models showing wide solution spread with this feature. Models also showing the H5 trough flattening out as it shifts E while high amplitude ridge builds toward Hudson Bay. Expect the NW upper flow that develops with this H5 ridge to bring high pressure into the region early next week. Can not rule out isolated diurnal convection during Monday, but should be mainly dry with seasonal temperatures early next week. Details... Thursday night...Will be a muggy and warm night as clouds increase from the NW. Looks like there will be fair chance for sct showers/thunderstorms, mainly after midnight. PWATs increase to 1.6 to 1.8 inches, so might see a few downpours with any convection. Temps will only fall back to the upper 60s to lower 70s, possibly warmer in the urban centers. Friday and Friday night...Model suite remains in pretty good agreement with stalled front across the region. Will see rather potent H5 short wave move along the front. Noting PWATs on order of 1.6 to 1.9 inches, highest along the S coast, with this feature. So, could see some heavy downpours especially in any convection. This signal has been increasing over the last few model runs, so have fair confidence that we may actually see some pretty good rainfall from this system. 00Z QPF suggests 0.5 to 0.8 inches of precip during this timeframe, highest amounts along the S coast. Big question will be whether this will be widespread or spotty, depending upon organization of the short wave as it comes across. Looks like pretty good elevated instability as TQ values up to around 20 during the day Friday into Friday evening. Also noting surface based LIs in the zero to -2 range and K indices in the lower 30s. Most parameters maximize during Friday afternoon/evening then tend to weaken Fri night. As short wave exits after midnight, should see slowly improving conditions across NW Mass. Will also see late night patchy fog with dewpts lingering in the 60s. Highs on Friday will be from 80-85 for most areas, a bit cooler along the coast. Saturday and Sunday...With the departing low, expect mainly dry conditions during Saturday. May see a few showers lingering across the region as a muggy airmass remains in place along with a light N-NE wind. Have kept slight chance of showers going for Saturday. May see another weak short wave move across during Sunday, but low confidence due to wide model solution spread. Have chance POPs going for this feature, mainly for sct showers. However, some instability works in across the E slopes of the Berkshires as well as S of the Mass Pike, so have mentioned possible thunderstorms there mainly from late Sunday morning into the evening. Monday and Tuesday...High pressure builds out of Quebec, with a drier NW flow in place. However, it is still summer so can not rule out a few isolated showers during Monday. Also have a slight chance of showers across the higher inland terrain Tuesday afternoon. Expect highs Monday in the lower-mid 80s, then in the mid-upper 80s on Tuesday.
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&& .AVIATION /09Z 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 Thursday/...High confidence. Today... VFR. Light wind will allow sea breezes to develop along the coastline starting late morning. Tonight... VFR. Light variable wind. Patchy fog possible with MVFR/IFR cigs/vsbys overnight. Thursday... VFR. Local MVFR cigs/vsbys in northern/western MA during the late afternoon due to scattered showers/tstms. KBOS TAF... VFR. High confidence. Light variable wind will allow a sea breeze to develop around 15Z. KBDL TAF... VFR. High confidence. Light variable wind. Outlook /Thursday night through Sunday/... Moderate confidence through the period. Thursday night...Mainly VFR. Areas of MVFR-IFR in patchy fog late at night mainly along the south coast. MVFR CIGS/VSBYS possible in any scattered showers/thunderstorms. Friday-Friday night...VFR early Friday, lowering to MVFR throughout the region by afternoon. Areas of IFR conditions possible in showers and scattered thunderstorms Friday afternoon/night. Locally heavy downpours possible. Areas of IFR in patchy fog Friday night. Saturday and Sunday...Mainly VFR, except MVFR CIGS/VSBYS possible in scattered showers. Chance for thunderstorms across E slopes of the Berkshires and S of the Mass Pike Sunday with local MVFR-IFR conditions. Potential for local MVFR-IFR in patchy fog and low CIGS after midnight both nights.
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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 Thursday/...High confidence. Winds remain below 25 knots and seas below 5 feet through the period. Sea breezes will develop near shore late this morning and afternoon. Winds become south to southwest Thursday. Outlook /Thursday night through Sunday/... Moderate to High confidence through the period. Thursday night...Winds and seas below small craft criteria. South winds 10 kt or less. Patchy late night/early morning fog with reduced visibilities. Isolated showers/thunderstorms possible. Friday-Friday night...Winds and seas remain below small craft, mainly S-SE winds Fri...becoming N-NE Friday night. May see gusts up to 15 kt Fri night. Reduced visibilities in patchy fog as well as scattered showers and thunderstorms. Best chance for showers from late Friday morning into Friday evening. Saturday and Sunday...Expect N-NE winds around 10 kt with gusts up to 15 kt Saturday morning, then becoming light/variable Saturday afternoon/night. Mainly E-SE winds 10 kt or less Sunday. Seas may build to around 4 ft on the southern outer waters Saturday night. Visibility restrictions in late night/early morning fog each day, and in scattered showers. Isolated-scattered thunderstorms possible Sunday, mainly on the waters south of the RI coast.
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&& .FIRE WEATHER... Dry conditions are expected to persist Today and Thursday across Southern New England. Minimum relative humidity values will be 30 to 40 percent inland both days, and 40 to 60 percent along the South Coast. Less wind Today than Tuesday, becoming a sea breeze along the coast late this morning and afternoon. Wind directions become more southerly on Thursday but remain below 15 knots. Concern for Thursday will be how far south showers/tstms reach. Most support is in Northern New England, but scattered showers/t-storms could reach Northern/Western MA late afternoon. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/EVT NEAR TERM...WTB SHORT TERM...WTB LONG TERM...EVT AVIATION...WTB/EVT MARINE...WTB/EVT FIRE WEATHER...WTB

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