Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 200807 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 407 AM EDT SAT AUG 20 2016 .SYNOPSIS...
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Isolated showers are expected at times through Sunday afternoon, but the vast majority of the time will be dry with increasing humidity. More widespread showers and thunderstorms with locally heavy rain will move through the region Sunday night as a cold front sweeps across the area. A few strong thunderstorms are possible. The showers will exit the eastern Massachusetts Monday morning followed by increasing sunshine and gusty winds. High pressure brings dry... cooler and noticeable less humid weather Tuesday with a gradual warming trend Wednesday through Friday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Gradual low level moisture return has allowed for spotty low clouds and fog patches to develop early this morning. Should see this burn off by mid to late morning in most locations. Otherwise, high pressure slowly moving east of the region will allow for a light south to southeast flow of air at the surface. This combined with some weak shortwave energy should generate isolated low topped showers later this morning and afternoon, mainly to the northwest of I-95. May see a bit more coverage across portions of the Worcester Hills and East slopes of the Berkshires with light upslope flow. Regardless, certainly not expecting a washout though and the vast majority of the day will be dry in a given location. While there is some Cape, opted to leave out thunder given shallow nature of the moisture. Partly sunny skies should allow high temps to generally reach the lower to middle 80s, but sea breezes will keep the immediate coast in the 70s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SUNDAY/...
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Tonight... Mainly dry weather expected tonight, but given weak warm advection a few spot showers will remain possible across interior southern New England. Should see more in the way of low clouds and fog patches develop overnight, particularly across the interior as the boundary layer cools. Low temperatures will mainly be in the lower to middle 60s. Sunday... Should see a mixture of clouds and sunshine, but probably more in the way of clouds across western MA/northern CT given model cross sections. While bulk of forcing will remain to our west, enough moisture/weak warm advection will be around for isolated to scattered showers mainly focused across western MA/Northern CT. Not expecting a washout though with the vast majority of the day ending up dry in a given location. Low risk of an isolated thunderstorm across the interior during the afternoon, but instability is rather marginal. High temps will be in the upper 70s to the middle 80s on Sunday, but it will feel humid with dewpoints between 65 and 70.
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&& .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/...
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Highlights... * T-storms w/locally heavy rain Sun ngt, few strong storms possible * Dry weather much of next week * A touch of Fall-like temps Mon night thru Tue night Sunday night ... Anomalous mid level trough exits the Great Lakes with its attending cold front sweeping across southern New England. This yields high confidence for a line of showers and T-storms to move across our region...roughly 03z to 09z west to east. Strong synoptic lift and frontal convergence coupled with PWATs briefly climbing over 2" will yield heavy downpours with a risk of brief localized urban/street flooding. Although the system is progressive and this will limit flood potential. Perhaps more concerning is the development of a surface wave on this approaching frontal boundary. While this will increase the heavy rain threat via convergence...increasing low level shear in vicinity of surface wave development along with high dew pts in the low 70s...low LCLs and MUcapes of 500-1000j/kg will yield a low risk of a few strong storms and a potentially brief tornado. While many mesoscale processes need to come into play for this to materialize and virtually impossible to predict at this time range...the synoptic background environment and time of year /warm SSTs not a limiting factor/ yields an enhanced risk for a brief tornado. Warm sector over the region with dew pts in the upper 60s and low 70s will result in a mild night with low temps only dipping to 65 to 70...along with humid conditions. Thus area will be primed for patchy fog. Monday... Good model agreement on deep layer moisture and lift offshore by 12z Monday. Thus any leftover showers/T-storms at sunrise will be confined to Cape Cod. Thus rapid drying from west to east across the region Monday morning. Breezy behind the front with secondary low strengthening over the ME coast then into the maritimes. Very pleasant with highs in the upper 70s to low 80s...low to mid 70s across the higher terrain. Turning much less humid as well with post frontal airmass accompanied by dew pts falling into the low 50s... refreshing! Monday night through Tuesday night... A sign of fall approaching as a 1026 mb Highs builds into the region this period...providing a cool and dry airmass with mostly clear skies and a touch of autumn as dew pts fall into the 40s! 850 mb temps drop to 6-8C Mon night before recovering late Tue. Highs Tue mostly 75-80 degrees with dewpoints in the 40s. Lows will drop into the 50s both nights with some upper 40s possible in the colder locations. Thus have leaned toward the cooler MAV temps esp Mon night into Tue morning. Wednesday through Friday... Subtropical ridge over the southeast states begins to build south of New England with rising heights over the northeast. This translates to a gradual warming trend...especially Thu and Fri as low level flow turns to the southwest. Highs will rise well into the 80s away from the shore Wed thru Fri. Dew pts still in check Wed with values in the 50s then slowly rising toward 60 Thu and well into the 60s Fri. So becoming more humid late next week. Mainly dry this period with a low risk of showers/T-storm late in the week as next northern stream short wave and attending cold front approach the area.
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&& .AVIATION /08Z 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. Short Term /through Sunday afternoon/... Today...Moderate to high confidence. Localized MVFR-IFR conditions in low clouds/fog patches should improve to VFR in most locations by mid to late morning. Otherwise, mainly VFR conditions expected with isolated showers likely later this morning and afternoon. Tonight...Moderate confidence. Cooling boundary layer and increasing low level moisture should allow areas of low clouds and fog patches to develop tonight. Timing and areal extent remain uncertain, but highest risk for low clouds and fog will be across western MA/northern CT. Sunday...Moderate confidence. Should see Cigs/Vsbys improve some by late morning, but still expect MVFR cigs at times for much of the region and even a low risk for localized IFR conditions across Cape/Islands. Isolated to widely scattered showers expected with focus across western MA/Northern CT. KBOS Terminal...Moderate to high confidence in TAF. KBDL Terminal...Moderate confidence in TAF. Outlook /Sunday Night through Wednesday/... Sunday night into Monday ... Moderate confidence. Lowering to MVFR/IFR from west to east as showers and sct t-storms move through 00-06z west and 06-12z east. Heavy rain likely with a few strong storms possible. Quick improvement to VFR from west to east late Sun night and Mon morning following wind shift to NW. Gusty post-frontal NW winds developing Mon. Tuesday and Wednesday...High confidence. VFR.
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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 afternoon/...High confidence. High pressure slowly moving east of the waters through Sunday afternoon will keep winds and seas below small craft advisory thresholds over this time. However, some 20 knot wind gusts are expected Sunday afternoon which may result in a period of choppy seas. Outlook /Sunday Night through Wednesday/...Moderate confidence. Sunday night into Monday ... South winds may briefly gust to 25 kt ahead of frontal boundary Sun night. Brief heavy showers and t-storm possible, mainly after midnight, then improving Mon morning. A few strong storms possible. Wind shifts to NW Mon morning with a few gusts to 25 kt possible Mon afternoon and evening. Tuesday and Wednesday...Light winds and seas. NW winds Tue and SW Wed but winds may become locally onshore over nearshore waters both days as seabreezes may develop. Excellent vsbys.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/Nocera NEAR TERM...Frank SHORT TERM...Frank LONG TERM...Nocera AVIATION...Frank/Nocera MARINE...Frank/Nocera

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