Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 280920 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 520 AM EDT SAT MAY 28 2016 .SYNOPSIS... Hot weather is on tap for all but portions of the immediate coast today. While the majority of the region will remain dry, isolated showers/thunderstorms will occur early this morning and again this afternoon. A backdoor cold front will bring cooler temperatures to eastern MA Sunday but it will remain very warm across the interior, where scattered showers and thunderstorms likely develop during the afternoon. Tropical moisture will bring showers with locally heavy rainfall very late Sunday night into Memorial Day. Dry conditions with warm afternoons follows Tuesday into Wednesday, but unsettled weather may return by the end of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Strong low level jet /with h925 W-SW winds up to 35-40 kt/ along with low level moisture and good elevated instability /TQ values up to around 20/ caused a line of showers and scattered thunderstorms that developed off the RI coast early this morning. This line continues to push E near and S of Martha`s Vineyard at 08Z. Expect the line to cross Nantucket and Nantucket Sound as well as the waters S of the islands, then should weaken with sunrise as it continues eastward. Also have noted a few showers that have moved into the mid Hudson valley into the central Berkshires at 08Z, which may hold together through sunrise across the CT valley of Mass. Noticing a band of mid and high clouds crossing the region on IR satellite imagery, but should push offshore by mid morning allowing for partly to mostly sunny skies. Once the sun does come out, expect temperatures to soar with very warm airmass across the region. Noting H925 temps up to +20C to +22C, and H85 temps at +15C to +16C early this morning. Good mid layer cap in place, up to H85 as seen on 00Z NAM and GFS model soundings, so this has to break in order get some convection going. BUFKIT soundings suggesting the convective temps need to reach the lower 90s to break the cap, which looks like it will happen especially across inland areas. Some question as the the timing of the precip, but have kept good continuity with previous forecasts. Kept slight chance to low chance POPs for this afternoon and evening mainly central and western areas, but can not rule out isolated convection somewhat closer to the coast. Will be tough along the S coast with onshore winds though. Expect daytime highs to reach the lower-mid 90s, with some of our long term climate locations possibly approaching or exceeding record levels. Check the climate section below for specifics.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
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Tonight...With continued S-SW wind flow in place, low to mid level moisture will continue to increase as dewpts will rise to the lower- mid 60s. Leftover showers/thunderstorms may reach toward the coast before dissipating this evening. May also see some patchy fog develop across the normally prone inland valley after midnight. Expect overnight lows mainly in the 60s, mildest in the urban centers. May see a backdoor cold front start to work southwestward down from the Maine coast overnight. Model guidance suggesting winds shifting to N-NE after 06Z around Cape Ann as well as temperatures dropping to around 60, and may reach close to Boston by daybreak. Sunday...Expect the backdoor cold front to push further S-SW during the day. The big question will be where this front will stall, as it appears it will stall somewhere across the region. This will be a catalyst for convection though, especially near and south of the front. Have at least slight chance POPs across most areas, but looks like best shot for convection will be from W of Fitchburg to W of Willimantic where better instability is also in place along with the mildest temperatures. SPC has a mention of general thunder for central and western areas.
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&& .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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Highlights... * Heavy rain showers Memorial Day with localized flooding possible * Mainly dry w/near or above normal temps Tue/Wed * Unsettled weather may return late Thu/Fri or next weekend Details... Sunday night and Memorial Day... Any left over scattered convection across interior southern New England will quickly diminish early Sunday evening with the loss of daytime heating. The rest of the evening will mainly be dry other than perhaps a spot shower or two, but some fog may develop. Things then become quite interesting very late Sunday night into Memorial day. Tropical depression 2 currently several hundred miles southeast of Charleston South Carolina is expected to become Tropical Storm Bonnie today. This storm is then expected to track northwest and approach the Carolina coast Sunday, then move very slowly northeast through the middle of next week remaining well south of our region. This tropical storm will not have a direct impact in southern New England, and none of Bonnie`s winds/storm surge will affect our region. While a direct impact will not occur, an approaching cold front will pull a plume of its tropical moisture northward into southern New England. PWATS approach or possibly exceed 2 inches, which will be near record high levels based on historical upper air data for this time of year. The guidance also signals the development of a SSW 30 to 40 knot low level jet by 12z Monday which is 2+ standard deviations above normal. This all means we should see bands of heavy rain showers develop very late Sunday night/early Monday morning. Given the anomalously high PWATS combined with the low level jet, there will be a risk for localized flooding. While the models do a very good job these days in indicating potential for heavy rainfall/localized flooding, they often struggle with the location. At this time, appears that a lot of the guidance is indicating an initial band of heavy rain showers across eastern NY state towards 12z Monday, close to the shortwave/better dynamics. Western MA and Northern CT may be on the eastern edge of this band, so this will have to be watched. It then appears that a second band may develop later Monday morning/afternoon across southeast MA/RI on the nose of a 40+ knot low level jet. Some of the guidance has this lingering into Monday evening, while other data dries us out by then. So in a nutshell, expecting numerous showers with locally heavy rainfall. Given the above parameters, it is certainly possible that a narrow swath may see 2+ inches of rain in less than an hour. So while widespread flooding is not expected...there certainly is potential for localized flooding especially if a heavy rain band sets up in one of our more vulnerable urban centers. Greatest risk for that appears to be in our far western zones and perhaps southeast New England on the nose of the low level jet, but again that certainly is subject to shift. Tuesday and Wednesday... Dry weather with warm afternoon highs into the 80s are anticipated away from the immediate coast Tue/Wed as a ridge of high pressure builds over the region. Dewpoints will drop back into the 50s though so will get rid of the humidity. Thursday into Saturday... Forecast confidence becomes quite low over this time. Upper level ridge will eventually break down by the end of next week. Whether that happens later Thu or holds off until next weekend is uncertain, but once that occurs unsettled weather will return.
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&& .AVIATION /09Z SATURDAY THROUGH WEDNESDAY/...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through 12Z...Moderate confidence. Mainly VFR conditions. May see local visibilities to MVFR-IFR in any patchy fog that may develop across the locally prone inland valleys and along the immediate coast. Sct showers/tstms with local IFR conditions passing near Martha`s Vineyard and Nantucket, which should start to weaken around 12Z. Today...Moderate confidence. Mainly VFR. Low risk for MVFR-IFR conditions in widely scattered showers and thunderstorms this afternoon away from the coast. Tonight and Sunday...Moderate Confidence. Mainly VFR. Local MVFR- IFR conditions in patchy fog late tonight into early Sunday morning. Low probability of brief MVFR conditions in SCT afternoon SHRA/TSRA across the interior. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Sunday Night through Wednesday/... Sunday night and Memorial Day...Moderate to high confidence. MVFR- IFR Cigs/Vsbys likely develop late Sunday night and continue into Memorial Day. This the result of low clouds...fog patches and heavy rain showers. Isolated thunderstorms are also possible. Monday night through Wednesday...Moderate to high confidence. Lingering MVFR-IFR conditions possible Monday evening, but improvement to VFR Tue continuing Wed.
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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 Sunday/...High confidence. Through 12Z...Expect winds and seas to remain below small craft. Will see S-SW winds gusting up to 20 kt on the southern outer waters. May see some patchy fog with locally lower visibilities. Locally heavy rainfall in sct showers/thunderstorms through 12Z on the waters near and S of Nantucket and Martha`s Vineyard. Today...S-SW winds gusting up to 20 kt through midday then will diminish. Leftover isolated showers/thunderstorms with locally heavy rainfall and reduced visibilities, as well as patchy fog through late morning. Tonight and Sunday...SW winds may gust up to 20 kt on the southern waters this evening, otherwise winds and seas below small craft criteria through Sunday. May see patchy fog with locally reduced visibilities tonight into Sunday morning. Outlook /Sunday Night through Wednesday/... Sunday night through Monday night...Moderate to high confidence. Quiet Sunday night on the waters other than some fog. We may see some southwest wind gusts to 25 knots develop Monday morning and continue into the afternoon with the aid of a low level jet along with heavy showers/isolated thunderstorms. Marginal 5 foot seas may also develop across our southern waters late Mon into Mon night. Tuesday and Wednesday...Moderate to high confidence. Lingering 5 foot swell possible across our southern waters Tue, but should diminish by late Tue night. Otherwise, a ridge of high pressure will keep winds/seas below small craft advisory thresholds with good visibility into Wed.
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&& .CLIMATE...
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Some of today`s record highs may be challenged as temperatures reach the lower-mid 90s. Record highs for today, Saturday May 28... Boston...92 set in 1931 Providence...91 set in 1931 Hartford...93 set in 1977 Worcester...88 set in 1911 and 1929 Milton/Blue Hill...90 set in 1929
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for CTZ003-004. MA...Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for MAZ004>007-009>018-026. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...Frank AVIATION...Frank/EVT MARINE...Frank/EVT CLIMATE...EVT

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