Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 281421 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1021 AM EDT SAT MAY 28 2016 .SYNOPSIS... Hot today away from the immediate coast. Mostly dry but isolated to scattered showers and/or thunderstorms will be possible. Into Sunday a backdoor cold front will drop south over E/NE Massachusetts behind which low clouds and poor visibility is expected, whereas along and ahead scattered showers and thunderstorms are likely. Late Sunday night and through Memorial Day, rain, locally heavy at times, and chances for thunderstorms associated with tropical moisture streaming north from Tropical Depression Number 2 expected. 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/... 1030 am update... Hot and mostly dry day with temperatures warming well into the upper 80s into the mid 90s, potentially record-breaking (see the climate section below). But there still remains the potential for isolated to scattered thunderstorms away from the immediate coast with the possibility of a rogue storm with heavy rainfall and gusts to 40 mph. More on that below. Evaluating 12z atmospheric soundings along with the latest high- res near-term guidance, interpreting an environment of weak shear with decent instability upwards of 1000 j/kg developing midday into afternoon beneath a mid to upper level ridge and warmer and drier air around H5. Convergence possible along immediate E MA coastal sea- breeze, and S flow against interior high terrain. And finally, boundary-layer becoming well- mixed up to H7 with a note- worthy inverted-V profile setup, especially where low to mid 90s are forecast breaking the cap more effectively per the warm- dry airmass around H5. Temperatures overall should easily exceed the convective temperature threshold. Taken altogether can not rule out low- to mid-layer convection albeit not especially deep, and considering the aforementioned environment, isolated to scattered activity. Think some of the high-res guidance is hinting upon areas of impact in the interior where it becomes warmest, and along the W-progressing sea-breeze. Thus the likelihood that most activity will be sub-severe though can not rule out that rogue storm. Activity to develop around midday and afternoon shifting E/SE into evening with the mean wind flow, so could see a repeat of last night with activity across the Cape and Islands though uncertain as to extent and magnitude. Just something to think about and to keep an eye out. Slight chance to chance PoPs away from the immediate coast. Again, highs from upper 80s into the mid-90s. S/SW winds overall with strongest along the S-coast with an E onshore sea-breeze along E MA. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/... 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. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... 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. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 14z update... Today...High confidence. VFR. Isolated to scattered TSRA to which TEMPO MVFR/IFR possible with 20-40 kt gusts away from the coast. Potential sea-breeze along the immediate E-coast. S winds overall around 5-10 kts. Tonight...Moderate Confidence. VFR. Isolated to scattered SHRA/TSRA erode SE across RI and SE MA early with potential MVFR implications. Otherwise BR or patchy FG possible E-coast MA and NW MA. Light winds. Sunday...Moderate Confidence. Winds back NE across E/NE MA with MVFR/IFR cig and vsby impacts. Towards the SW of this wind shift, SCT SHRA/TSRA expected with TEMPO MVFR/IFR impacts and possible 20-40 kt gusts. Focus around midday into afternoon. S winds overall for those areas S/SW of the NE wind shift. KBOS TAF...VFR. Potential seabreeze around midday into early afternoon. Will keep the terminal dry. As for Sunday, still evaluating as to whether winds back NE and MVFR/IFR conditions sulk S. Terminal may remain on the cusp in an area of convergent flow with winds from the S versus winds from the NE. KBDL TAF...VFR. Potential isolated to scattered SHRA/TSRA developing around early afternoon. Higher confidence into Sunday for convective activity and TEMPO MVFR/IFR. S winds prevailing. 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. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday/...High confidence. 1030 am update... Today...S-SW winds gusting up to 25 kt through midday then will diminish. Seas 2 to 4 feet. Can not rule out some small craft advisory conditions along the S waters. 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. && .CLIMATE... 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 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Air Quality Alert until 11 PM EDT this evening for CTZ002>004. MA...Air Quality Alert until 11 PM EDT this evening for MAZ004>007- 009>018-026. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/EVT NEAR TERM...Frank/Sipprell/EVT SHORT TERM...EVT LONG TERM...Frank AVIATION...Frank/Sipprell/EVT MARINE...Frank/EVT CLIMATE...WFO BOX Staff is the U.S. government's official web portal to all federal, state and local government web resources and services.