Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 262308 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 710 PM EDT Wed Apr 26 2017 .SYNOPSIS... A few showers, along with areas of drizzle and fog will persist tonight into Thursday, especially along the coast. A fast moving disturbance may bring a few more rain showers and perhaps an isolated thunderstorm very late Thursday night into mid morning Friday, with mainly dry and warm weather for Friday and Saturday afternoons. A backdoor cold front crosses the region Saturday night, bringing much cooler weather on Sunday especially along the coast. Another cold front will likely bring a period of showers sometime Monday into early Tuesday. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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***Dense Fog tonight across portions of eastern New England particularly along the eastern MA coast, Cape, and Islands*** 710 pm update... Weakening vertically stacked system with a light moist onshore was resulting in dense fog along much of the eastern MA coast and the Worcester Hills early this evening. As boundary layer cools a tad, may see this dense fog expand further west, so dense fog advisory continues overnight across the eastern half of southern New England. This dense fog will be accompanied with areas of drizzle and a few showers at times, given weak warm advection aloft. Further inland across western MA/northern CT mainly dry weather will dominate other than perhaps a spot shower overnight. Will have to watch this area for some fog developing later tonight as well, but should not be as dense or widespread. Low Temps will only drop into the 50 to 55 degree range given relatively high dewpoint air in place and cloud cover.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH 6 PM THURSDAY/... Weak surface low washes out as it lifts northeast of our area, but still have the mid level low passing near the Cape/Islands during the day. Will continue to have weak onshore flow. Areas of fog in the morning, with visibility gradually improving. Cloudy skies anticipated thru the day, with lingering drizzle eastern MA/RI. Can`t rule out some patchy measurable light rain in eastern MA and RI. Continuing to think that MOS guidance is likely a little too high with max temperatures Thursday, so will utilize the lower consensus of raw model 2 meter temperatures for max temperatures. && .LONG TERM /THURSDAY NIGHT THROUGH WEDNESDAY/... Highlights... * Brief scattered showers and perhaps an isolated t-storm possible very late Thu night into mid morning Fri * Dry/very mild to warm temps expected by Friday afternoon * Warm on Sat away from the south coast with the low risk for a few afternoon/early evening t-storms * Turning much cooler Sat night and Sun especially on the coast * Period of showers likely sometime Mon into early Tue Details... Thursday night and Friday morning... Still a lot of lingering low level moisture trapped beneath the subsidence inversion based on model cross sections Thu night. Therefore, feel there will be an abundance of low clouds and fog patches with even some drizzle possible. The clouds and low level moisture should keep low temperatures mainly in the lower to middle 50s. The majority of Thu night will be dry, other than perhaps some drizzle. However, a fast moving shortwave approaches the region toward daybreak Friday with a burst of elevated instability. This will probably result in a brief band of scattered showers and perhaps a few embedded thunderstorms. Activity should be scattered and short-lived with it mainly coming to an end by mid to late Friday morning. Friday afternoon... Steep mid level lapse rates along with decent instability/shear develop by Friday afternoon as temps warm with dewpoints in the 50s. However, subsidence behind the morning shortwave and very dry mid levels of the atmosphere should result prevent convection from developing Friday afternoon. Therefore, expect dry weather and with plenty of sun Friday afternoon. Highs should recover in the 70s to near 80 away from the marine influence of the south coast. Friday night... Upper level ridge off the southeast coast will pump unseasonably mild air into southern New England. Low temps should only drop into the middle to upper 50s in most locations. May also see some patchy fog develop given relatively high dewpoints in place. Saturday... A rather warm day appears to be in the cards away from the south coast, Cape and Islands. Given west to southwest flow out ahead of an approaching pre-frontal trough/cold front, should see high temps reach 80 to 85 in many locations. At the same time, a pre-frontal trough will be dropping south into the region but it is uncertain if it will trigger a few thunderstorms during the afternoon. While there are impressive wind fields along with some instability, forcing will be limited. The models actually show subtle height field rises during the afternoon, which is not normally a good sign for convection. Much of the guidance also pushes the plume of steeper mid level lapse rates south of the region by Saturday afternoon. Nonetheless, "If" a few thunderstorms are able to develop the risk for an isolated strong to severe t-storm or two would exist given impressive wind fields. Currently, we will consider this a low risk given limiting factors stated above, but certainly something will have to watch with pre-frontal trough. Saturday night and Sunday... Despite upper level ridging, a strong high pressure system will build into eastern Canada. This will send a backdoor cold front south of the region Sat night and result in much cooler temps on Sun. Highs Sunday will probably only in the 50s along the coast with 60s further inland. May see a spot shower or two Sat night/Sun, but the vast majority of the time will feature dry weather given lack of forcing. Monday into Tuesday morning... Low pressure across the central Plains will lift northeast across the Great Lakes Monday and then into eastern Canada Tue. Some over running showers are possible early Monday, but a period of steadier showers with even brief heavy rainfall will be possible later Mon into early Tue with the cold front. Temps highly uncertain on Mon as a frontal boundary may be jammed up across the region. Overall, coolest temps probably in northeast MA and mildest in our CT zones. Tuesday afternoon into Wednesday... Low confidence given the time range, but most guidance suggests mainly dry and pleasant weather as a weak ridge of high pressure builds in from the west. && .AVIATION /00Z THURSDAY THROUGH MONDAY/...
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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/... Tonight...Moderate to high confidence. Mainly IFR to LIFR conditions with the most widespread/lowest conditions across the eastern MA coast, Cape and Islands. This a result of dense fog, drizzle and scattered showers. Thursday...Moderate confidence. Conditions improve to MVFR across the interior. Meanwhile along the coast, LIFR conditions should improve by late in the morning/afternoon but probably only to IFR thresholds given moist onshore flow. KBOS TAF...Moderate to high confidence in TAF. KBDL TAF...Moderate to high confidence in TAF. Outlook /Thursday Night through Monday/... Thursday night into mid morning Friday...Moderate confidence. Mainly MVFR/IFR conditions in low clouds and fog patches Thursday night and early Fri morning. Also, a brief period of scattered showers and perhaps an isolated t-storm are possible very late Thu night into mid morning Fri. Late Friday morning and afternoon. Moderate to high confidence in mainly VFR conditions. Saturday and Sunday...Moderate confidence in mainly VFR conditions. Monday...Moderate confidence. MVFR/IFR conditions possible in lower clouds and some showers, particularly late Mon/Mon night.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High confidence. 4 pm update... Tonight... Low pressure continues to weaken as it lifts from south of Long Island northeastward into the southern New England coastal waters tonight. Gale Warning that was previously in effect for the southeastern coastal waters has been allowed to expire. Small Craft Advisory is in effect until 8 pm for Cape Cod Bay/Buzzards Bay/Vineyard and Nantucket Sounds for gusts to 25 kts, with winds diminishing. For the remainder of the coastal waters excluding Boston Harbor and Narragansett Bay, a Small Craft Advisory continues thru tonight. Visibility restrictions at times across the waters thru tonight in locally dense fog. Thursday... Low pressure weakens further as it lifts northeast of the waters. Winds will expected to be around 10 kt or less. However due to lingering swell, Small Craft Advisories will continue to be needed across the outer coastal waters as well as RI and BI Sounds. In addition, areas of drizzle, fog or patchy rain will lead to some visibility restrictions on the coastal waters. Outlook /Thursday Night through Monday/... Thursday night and Friday...Moderate to high confidence. Despite winds 20 knots or less, lingering southeast swell will result in marginal small craft seas persisting across the outer-waters and western sounds. Areas of fog may result in poor visibility for mariners Thu night into mid morning Friday. Saturday and Sunday...Moderate to high confidence. Winds and seas mainly below small craft thresholds, but some marginal small craft seas for a time on Saturday across our southern waters. May also see some near shore southwest wind gusts of 20 to 25 knots Sat afternoon. Monday...Moderate confidence. Winds and seas will probably increase to small craft thresholds on gusty southerly winds late Mon and especially Mon night ahead of the next cold front. && .TIDES/COASTAL FLOODING... * Isolated minor coastal flooding impacts during astronomically high tide tonight along the east and south coasts We are in a spring tide cycle with high tides that are astronomically high. This combined with an anticipated storm surge of around 1 foot may set the stage for isolated pockets of minor coastal flooding along both south and east coasts around the time of high tide tonight. The astronomical high tides remain very elevated through the end of the week. Due to the breadth of the fetch, we may encounter enough wave action with lengthening periods on top of an elevated tide to cause pockets of erosion tonight along the Martha`s Vineyard south coast, Nantucket south and east coasts, and the outer Cape ocean side from Truro to Chatham. Boston High Tides (flood stage at Boston 12.5 feet)... 11.92 feet / Thursday 12:07 am Providence High Tides (flood stage at Providence 7 feet)... 6.21 feet / Wednesday 9:00 pm && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...Dense Fog Advisory until 9 AM EDT Thursday for CTZ004. MA...Dense Fog Advisory until 9 AM EDT Thursday for MAZ005>007- 012>024. RI...Dense Fog Advisory until 9 AM EDT Thursday for RIZ001>008. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ231>234. Small Craft Advisory until 6 AM EDT Friday for ANZ235-237-250- 254>256. Small Craft Advisory until 9 AM EDT Thursday for ANZ251.
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&& $$ SYNOPSIS...NMB/Frank NEAR TERM...Frank/NMB SHORT TERM...NMB LONG TERM...Frank AVIATION...NMB/Frank MARINE...NMB/Frank TIDES/COASTAL FLOODING...Staff

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