Area Forecast Discussion
Issued by NWS Boston, MA

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183 FXUS61 KBOX 271411 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1011 AM EDT Tue Jun 27 2017 .SYNOPSIS... A strong jet stream will result in widespread afternoon showers and thunderstorms across Massachusetts, Rhode Island and Connecticut. A few of the storms may contain gusty winds and small hail. A warming trend begins for the latter half of the week with a return to summer heat and humidity Friday and Saturday. A warm front may bring some showers and some thunderstorms Thursday night, with more showers and thunderstorms possible Friday through the weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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A band of showers is moving northeast across RI and into SE Mass, associated with a weak shortwave that is mostly visible in the low level fields. Lightning detectors have shown a few flashes and pulses with this line. These should be clear of eastern Mass around midday. A second zone of clouds may sweep across our region midday/early afternoon but should then move off. Expect periods of sun much of the afternoon that will allow for some solar heating. Temps at the top of the mixed layer will be 8-10C or its equivalent, so we expect max sfc temps 75-80. We continue to watch the potential for strong thunderstorms this afternoon/evening. Morning soundings show an elevated dry adiabatic lapse rate reaching 700 to 750 mb, 850 mb winds around 25 knots, and 500 mb winds 50-60 knots. Cold temperatures aloft are giving us stability parameters favorable for convection. Synoptically, A sharp upper trough is moving through the Eastern Great Lakes with a 120-knot upper jet moving around the base of the trough and across New England. Our area will mainly be on the left entrance region of the jet rather than one of the more favored areas for upper venting. Wet bulb zero values this morning ranged from 6700 feet at Albany to 8800 feet at Brookhaven NY...Gray ME and Chatham were 7300-7400 feet. We note SPC has areas west of I-95 in a Marginal Risk for severe weather. Considering all of this, we will maintain some enhanced wording for strong winds and small hail in the forecast. Observed winds aloft in the projected mixed layer this morning were 20-25 knots. Model guidance forecasts a range of 20-30 knots during the afternoon. Expect afternoon wind gusts of 20-25 knots, with some potential for gusts of 25-30 knots.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Tonight... Cyclonic flow continues along with cold temps aloft and 40-45 kt of deep layer shear. This will support leftover showers and isolated T- storms to persist into the evening (especially over RI and eastern MA) before taping off after midnight. Patchy fog possible given leftover low level moisture from earlier storms Wednesday... Mid level flow is still cyclonic however flow becomes more WNW which results in column drying out along with surface dew pts falling into the 40s. Cyclonic flow aloft combined with cold temps will yield plenty of diurnal clouds and the risk of an isolated shower/T-storm. However given lack of moisture areal coverage should be limited to isolated. Otherwise a fairly nice day by late June standards with a mix of sun and clouds, highs 75-80 along with comfortable humidity with dew pts in the upper 40s and low 50s! && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Highlights... * Thunderstorm chances increase Thursday night through Sunday * Heat and Humidity return Friday, lasting into the weekend Pattern Details... 00z guidance is in general agreement synoptically with some difference in strength and timing for each wave late in the week. Upper level trough axis will begin to push offshore on Wednesday resulting in a quasi-zonal flow for the region beginning on Thursday. The upper level pattern will become more amplified by the weekend resulting in a broad trough over the Great Lakes with sub- tropical ridge building over the weekend. Because of the ridging over the East Coast and the Midwest trough, a cold front will be come nearly stationary with very little eastward progress this weekend. Ridging out West by Sunday will push towards the Great Lakes by early next week, pushing the broad upper level trough over the Northeast. Details... Wednesday night into Thursday... Surface high pressure over the region Wednesday night will help keep winds light and skies clear. Overnight lows will drop into the mid to upper 50s with metro regions in the 60s. Dry day to start on Thursday as high pressure will slide offshore. The flow will turn more active with zonal flow aloft and a few weak waves passing through. Impressive warming aloft as surface warm front pushes through the region. This will push southern New England in the warm sector resulting in increasingly warm and humid temperatures. A weak shortwave will move through the flow Thursday evening/night. With zonal pattern and both 850mb isotherms and winds becoming parallel, appears that anything the fires across upstate NY will ride through the flow moving into the area. In fact, guidance is indicating a lingering MCS will move through the flow late in the afternoon/evening which could result in a few strong storms, esp north of the Pike. However, new convection could refire along its southern edge given the strong low level jet and moisture over the area. Trends will have to be watched. Depending on the outcome of convection and cloud cover, temperatures will remain in the low 80s. But it will feel warmer as humidity will be on the rise. Showers and thunderstorms will continue during the overnight hours keeping temps in the upper 60s. Friday into Sunday... Unsettled weather pattern for this time period as southern New England remains in the warm sector with heat and humidity. 850 mb temps warming to 17-18C as well as southwesterly flow, will allow for the summer heat to returns to the region. Appears that the potential for 90 degrees is possible on Friday and Saturday as the back door cold front continues to remain well north of the region. Heat headlines may be needed as 70F dewpoints beginning to pool into the area. There remains a chance for showers and thunderstorms each day, but difficult to place the exact timing and location of any strong storms due to lack of surface boundary. Daytime heating will allow for scattered showers and thunderstorms to develop on Friday. Another shot for scattered showers and thunderstorms will develop on Saturday, but western locations have the better shot thanks to approaching pre-frontal trough. Lower confidence for eastern locations as subtropical ridge will build in pushing a dry slot into the area on Saturday. Cold front will approach on Sunday triggering another round of showers and thunderstorms for southern New England. Through this period, the potential for strong to severe weather appears possible as the region remains in the warm sector. Plenty of instability and moisture will continue to pool into the area with 0- 6 km shear values around 30 kts. Main risk will be strong gusty winds as well as heavy downpours as PWATs will be above 1.5 inches. Still uncertainty with this portion of the forecast so stay tuned for updates. Monday... Cold front will slowly pass through the region on Monday, however is appears that it may get hung up. Cyclonic flow aloft with southwest flow in the mid-levels may trigger another round of showers for the area. Low confidence on this portion of the forecast as there is still a spread in the guidance. && .AVIATION /14Z 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. 7 AM update... Short Term /through Wednesday/...High confidence. This afternoon... VFR. Periods of MVFR cigs/vsbys possible in heavier showers and embedded T-storms this afternoon/evening. A few of the stronger storms may contain gusty winds and small hail. Increasing pressure gradient will result in gusty SSW winds even in the absence of T-storms. Tonight... Marginal VFR-MVFR in scattered showers and T-storms during the evening, especially across eastern MA and RI. Activity should diminish after midnight. Wednesday... VFR and drier weather. Although can/t rule out an isolated shower/T-storm during the afternoon. Modest WNW winds. KBOS Terminal...High confidence in TAF. Showers and T-storms likely this afternoon. A few of the stronger storms may contain small hail and gusty winds. KBDL Terminal...High confidence in TAF. Showers and T-storms likely this afternoon. A few of the stronger storms may contain small hail and gusty winds. Outlook /Wednesday Night through Saturday/... Thursday...High confidence. Mainly VFR. Afternoon/evening showers possible in the interior with showers/t-storms possible all SNE Thu night. Gusty SW winds to 25-30 kt developing, especially coastal plain. Friday into Saturday...Moderate confidence. Patchy early morning fog each day. Otherwise mainly VFR, except local IFR in possible strong thunderstorms, mainly during the afternoon and evening hours through the period.
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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/...High confidence. This afternoon... SSW winds increase up to 25 kt along the RI and MA coastline. Strongest winds near shore and occurring from noon to 6 pm. SCA posted for all the near shore waters. Showers and T-storms develop this afternoon. A few strong storms possible especially north shore of Boston. Tonight... Showers and thunderstorms most numerous during the evening hours. A few strong storms possible with gusty winds and small hail. SSW winds may yield patchy fog especially during the evening. Improving after midnight. Wednesday... Winds become WNW at modest speeds. This results in good vsby and mainly dry weather, other than an isolated shower or T-storm. Outlook /Wednesday Night through Saturday/... Thursday...Moderate confidence. Small craft advisories will likely be needed. Increasing SW winds with gusts to 25+ kt likely, especially over nearshore waters. Building seas may reach 6 to 8 ft over southern waters Thu night. Friday into Saturday...Moderate confidence. SW winds continue, mainly 20-25 kt with building seas. Scattered thunderstorms, some with reduced visibilities and strong gusty winds for each day.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230>237-251.
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&& $$ SYNOPSIS...Nocera/Dunten NEAR TERM...WTB/Nocera/Dunten SHORT TERM...Nocera LONG TERM...Dunten AVIATION...Nocera/Dunten MARINE...Nocera/Dunten

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