Area Forecast Discussion
Issued by NWS Boston, MA

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494 FXUS61 KBOX 260200 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1000 PM EDT Sun Jun 25 2017 .SYNOPSIS... Scattered showers and isolated thunderstorms will diminish by midnight. Additional upper level disturbances move across New England on Monday and Tuesday, bringing a few showers or isolated thunderstorm. Then a warming trend begins for the latter half of the week with a return to summer heat and humidity by Friday. A warm front may bring some showers Thursday with more showers and thunderstorms possible Friday and Saturday. A backdoor front may drop south into the region Saturday. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/... 10 PM update... Area of showers and isold t-storms moving through MA have developed in the right entrance region of the upper jet. Wind gusts to 30-40 kt have been reported. More showers are developing in eastern NY and HRRR indicates these will hold together as they move across the MA Pike region next few hours. Updated PoPs to reflect current trends and hi-res guidance. Previous discussion... Lingering instability along with the right entrance region of the upper jet...this may support a few showers/tstms through the first hours of the night. Upper shortwave moving along the Canadian border moves off to the northeast tonight. The instability will diminish and the upper jet will shift southeast during the night, so expect any showers to end and skies clear. Clearing skies and light wind will allow some radiational cooling. With dew points in the 50s, expect min temps mainly in the 50s...except low 60s in some urban centers. && .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Upper flow remains cyclonic. A weak shortwave moves through the flow and across New England on Monday. Temps aloft will be a couple of degrees cooler, with solar heating working on the surface temperatures. The resulting lapse rates should be favorable for a few showers/tstms. Mixing will again reach high, up to 800 mb or a little higher. Temps at that level, equivalent to 11C at 850 mb, will support max temps in the upper 70s and the low 80s. Convection will again diminish after sunset with clearing skies and light wind. With dew points in the 50s, expect min temps in the 50s and low 60s. && .LONG TERM /TUESDAY THROUGH SUNDAY/... Highlights... * A few showers/isold t-storm possible Tue/Wed * Warming trend toward end of the week with return to summer heat/humidity by Fri * Thunderstorm chances increase Thursday night through Saturday * Low confidence - Backdoor front possible far northeast MA Sat. Overview... Mid level trough exits New England Wed., followed by building heights as subtropical ridge builds over the western Atlantic. Polar jet will be in the vicinity of New Eng next weekend which will leave us susceptible to weak shortwave passages. A warm front will meander back and forth near the MA/NH border Friday through Sunday with a series of weak low pressure systems moving along the boundary. Thus the chance of showers and thunderstorms will increase as we head into the weekend. Details... Tuesday and Wednesday... Strong mid-level shortwave trough lifts northeast from the Great Lakes Tue with axis of the trough moving into New England by Tue. evening before exiting on Wed. With 500 mb temps cooling to -18 to -20C, will see scattered showers and isolated thunderstorms. The best chances, where K Indices reach 25-30 along with Total Totals greater than 50, will be in the northwest half of the region, west of a line from northern CT to the Merrimack Valley. For the second run in a row, the ECWMF shows a surface trough south of New England, which creates an area of rain showers for south coastal RI and southeast MA Tue. night into early Wed. morning. Will forecast a chance of showers there. On Wed, mid level trough exits the region. There will still be a cold pool aloft, hence Total Totals Indices in the lower 50s. However, the column will be drying out with westerly winds and K Indices struggling to surpass 20-25. Cannot rule out a slight chance of a few showers. But not expecting thunder. Highs both Tue. and Wed. from 77 to 80 in the interior. Thursday... Increasing warm advection pattern as warm front approaches from the SW will lead to increasing clouds. Southwesterly low level jet is forecast to increase to 40-50 kt at 850 mb by late in the day. Despite some cloud cover temperatures will rise to the mid 80s and this will allow for mixing to create wind gusts to 20-30 mph, especially in the coastal plain. GFS and ECMWF now in agreement that the warm front will move to near the MA/NH/VT border by Thu. evening. There is a pronounced increase in K Indices as high theta-e air moves in from the west. The implication is that a cluster of thunderstorms, possibly severe to our west, will travel eastward along the warm front, aided by swift 55-70 kt west winds at 500 mb. There is a good chance of thunderstorms in northern and western MA late Thu. afternoon and Thu. night as a result, with scattered storms possible elsewhere Thu. night. Friday and Saturday... Somewhat tricky forecast due to placement of active frontal boundary. Very unstable air mass in place both Fri. and Sat. High temperatures will reach well into the 80s with near 90 possible. Dewpoint temperatures are forecast to hover between the upper 60s and lower 70s. The frontal boundary is forecast to become quasi- stationary near the MA/VT/NH border by Saturday...and it may even shift southward a tad as a backdoor cold front into the Cape Ann region on Saturday. Several thousand Joules of CAPE are possible on either day. Scattered thunderstorms are expected both days and there is the potential for severe weather, with wet microbursts a possibility. Helicity values could be higher near the MA/NH/VT border, close to the front, which may add to severe potential. Sunday... Tricky forecast continues...with models suggesting a slow moving surface trough and a continued chance of scattered showers and thunderstorms. Highs mainly in the mid 80s due to cloud cover, but subject to change...could be higher if more sunshine. && .AVIATION /02Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. 654 PM update... Tonight... VFR. Scattered showers and isolated thunderstorms will progress eastward across portions of southern New England tonight, exiting the coast around 04-05Z. Brief MVFR vsbys in any showers. Clearing skies overnight with light winds. Monday into Monday night... VFR. Daytime heating will develop cumulus clouds with bases 4000-5000 feet. These will lead to scattered showers and a few thunderstorms. Brief vsbys below 5 miles in any showers. Clouds and showers dissipate after sunset. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Tuesday through Friday/... Tuesday and Wednesday...High confidence. Mainly VFR. A few showers and isold t-storms possible Tue and still can`t rule out a shower on Wed. Thursday...Moderate confidence. Mainly VFR with cigs lowering from NW to SE. Afternoon 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...Moderate confidence. Patchy early morning fog, with local MVFR. Then VFR, except local IFR in possible strong thunderstorms, mainly during the afternoon and evening hours. MVFR in patchy fog late Friday night, especially south coast. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. High pressure offshore with west to southwest winds. Speeds should remain 20 knots or less. Seas have diminished, and should remain at 4 feet or less through the period. Outlook /Tuesday through Friday/... Tuesday and Wednesday...High confidence. Quiet boating weather with winds and seas below SCA. Gusts to 20 kt possible nearshore waters. 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. Chance of showers and thunderstorms Thursday night. Friday...Moderate confidence. SW winds continue, mainly 20-25 kt with seas 4-8 ft over the southern waters and 3 to 6 ft over the eastern waters. Scattered thunderstorms, some with reduced visibilities and strong gusty winds. && .TIDES/COASTAL FLOODING... High astronomical tides have peaked at most spots, but still at high levels for at least one more cycle. The overnight tide cycle will be the one of concern, with Boston reaching 12.2 feet after midnight tonight. Tidal departures will be around 0.3 to 0.4 feet along the Massachusetts East Coast. This means conditions will be high enough along the Mass East coast for at least some minor splashover at high tide. Subsequent high tides will be trending lower, and thus less of a risk for splashover concerns. && .EQUIPMENT... KBOX radar is down. Technicians have been notified and will be looking into the problem. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/GAF NEAR TERM...WTB/KJC SHORT TERM...WTB LONG TERM...GAF AVIATION...WTB/GAF MARINE...WTB/GAF TIDES/COASTAL FLOODING... 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