Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 251915 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 315 PM EDT Sun Jun 25 2017 .SYNOPSIS...
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Scattered showers and isolated thunderstorms will diminish early tonight. 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.
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&& .NEAR TERM /THROUGH TONIGHT/...
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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 shortweave 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.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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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.
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&& .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 * A few showers possible Thu with sct showers/t-storms Fri/Sat * Backdoor front possible Sat but low confidence Overview... Mid level trof will begin to exit the northeast Wed, followed by building heights as subtropical ridge builds over the western Atlantic. Polar jet will be in the vicinity of New Eng late in the week into the weekend which will leave us susceptible to weak shortwave passages and bouts of showers and t-storms. Temps starting out slightly below normal Tue then warming through the end of the week. Will have to watch a backdoor front for next Sat. Details... Tuesday and Wednesday... Fairly robust shortwave lifts NE from the Gt Lakes Tue with mid level trof moving into New Eng by Tue evening before exiting on Wed. Increasing dynamic forcing and 500 mb temps cooling to -18 to -20C will bring sct showers and isold t-storms to SNE Tue into Tue evening with best chance in the interior. ECMWF is showing a more amplified trof with a second shortwave rotating around and inducing a coastal low south of New Eng Tue night with area of rain for SE New Eng. This does not have support of other global models so we have discounted for now but something to watch in later forecasts. On Wed, mid level trof begins to exit the region but 500 mb temps around -21C through 18z before warming toward evening. Moisture is limited but can`t rule out a few showers given the rather cold temps aloft. Temps mid/upper 70s Tue and a few degrees warmer on Wed. Thursday... Increasing warm advection pattern as warm front approaches from the SW will lead to increasing clouds. GFS and ECMWF differ on the positioning of the warm front which impacts sensible weather and temps. GFS lifts the front to the north with main focus for showers/t-storms to the north and west. ECMWF holds the front to the south with wetter and much cooler conditions. A low confidence forecast this far out so minimal changes were made to PoPs and temps and will have chc pops in the interior. Higher theta-e air and better instability remains to the west where best t-storm chances are. Gusty SW winds developing, especially in the coastal plain as low level jet develops. The risk for t-storms will increase Thu night as higher theta-e air moves in. Friday... Warm sector airmass with low level theta-e ridge axis across the region and decent instability so expect sct showers and t-storms developing. Difficult to pinpoint shear profiles this far out but it does appear the region will be on the southern edge of stronger deep layer shear so severe weather is possible. Temps should reach well into the 80s to near 90 degrees but cloud cover could have some impact. Very humid with dewpoints near 70. Saturday... Tricky forecast as we may be dealing with a backdoor front close to New Eng. Impossible to know where this front will be but there is potential for a sharp temp gradient across the region depending on where the front is located. Very warm/humid south of the front with temps well into the 80s but much cooler to the north of the boundary with 60s possible. It will all depend on where the front is. Continued risk for showers/t-storms, mainly south and west of the boundary. && .AVIATION /19Z SUNDAY THROUGH FRIDAY/...
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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 Monday Night/...High confidence. Tonight... VFR. Evening showers and scattered thunderstorms, especially in Western and Central Mass, will diminish. 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-storm 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 developing, especially coastal plain.
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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 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. Increasing SW winds with gusts to 25+ kt likely, especially over nearshore waters. Building seas may reach 8 ft over southern waters Thu night. Chance of showers and thunderstorms Thursday night.
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&& .TIDES/COASTAL FLOODING...
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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.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...None.
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&& $$ SYNOPSIS...WTB/KJC NEAR TERM...WTB/KJC SHORT TERM...WTB LONG TERM...KJC AVIATION...WTB/KJC MARINE...WTB/KJC TIDES/COASTAL FLOODING...

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