Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 192005 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 405 PM EDT FRI AUG 19 2016 .SYNOPSIS...
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Mainly dry weather prevails through Saturday with just a low risk of a spot shower. Humidity levels will increase Sunday with a few showers or a thunderstorm possible, mainly across western areas. More widespread showers and thunderstorms with locally heavy rainfall will move through Sunday night as a cold front sweeps across the region. The showers will exit the southeast New England coast Monday morning followed by increasing sunshine and gusty winds. High pressure brings dry and cooler weather Tuesday with a gradual warming trend Wednesday through Friday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/... 210 PM Update... Fair weather cumulus clouds have developed across most areas away from the coast this afternoon. Dewpoints have dropped to the mid and upper 50s across most of Mass away from the immediate coast with drier air on light N-NW winds, while they hold in the lower-mid 60s across RI/N CT as well as on Martha`s Vineyard and Block Island. Some question remains whether isolated showers will develop across portions of Conn into W RI with pooling of low level moisture and modest low level convergence due to the sea breeze. Noting a few showers beginning to develop across W CT and central Long Island, which are tending to move SE with prevailing NW winds in the mid levels. Also noting marginal K values across central CT southward, keeping more stable air across the region even with a weak H5 short wave moving across. At this point, should remain mainly dry for most areas, but can not rule out a stray shower into N CT and extreme W RI, but should not last long. Will keep the mainly dry forecast going. Temps mainly in the lower-mid 80s even down to the coast, except holding near 80 along the immediate east coast with sea breezes in place. Have updated forecast to bring conditions current and incorporated into near term trends through the remainder of the afternoon. && .SHORT TERM /6 PM THIS EVENING THROUGH SATURDAY NIGHT/... Tonight... Another good setup for radiational cooling as pres gradient remains weak clearing skies is expected with enhanced mid lvl ridging, and dwpts are drier by afternoon mixing. More widespread upper 50s and low 60s. This will also lead to increased fog potential across the interior as weak return flow develops aloft with moisture trapped beneath the subsidence inversion. Will need to monitor typically prone valleys. Sat... Continued height rises as high pres shifts to the E and allows for return flow to develop, although weak. The increased moisture suggests higher risk for interior cloud development, which combined with the cooler start should yield slightly cooler highs, mainly in the low-mid 80s across the region. In spite of the increase in low-lvl moisture, the building heights should limit shra development, so will continue with NIL pops. && .LONG TERM /SUNDAY THROUGH FRIDAY/...
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Highlights... * Showers/t-storms with locally heavy rain Sun ngt, exiting the coast early Mon * Dry and cooler Mon night into Tue night * Warming trend Wed through Fri Overview... Model guidance in good agreement on timing of mid level trof and attending cold front Sun night into early Mon. Some timing changes still possible but trend for a faster solution continues which should confine bulk of rainfall confined to Sun night. The trof and post frontal airmass will deliver cooler and much drier airmass later Mon into Tue night with slightly below normal temps, then subtropical ridge builds back north along the east coast with warmer temps returning for the mid to late week period. Next approaching trof may introduce threat of convection by next Fri. Sunday... Some low clouds expected to start the day Sun then skies should gradually become ptsunny. Model guidance all generating some light QPF during Sun, especially away from the coast, likely in response to higher theta-e air moving in from the west. Instability marginal so looking at mainly a few showers but thunder chances increase later in the day in western New Eng. Temps seasonable 80-85 degrees with increasing humidity as dewpoints climb to near 70. Sunday night... A period of showers and sct t-storms likely as mid level trof approaches and cold front moves into SNE. A plume of subtropical moisture with PWATs 2+" surge north ahead of the front with right entrance region of upper jet providing favorable synoptic lift for locally heavy rainfall. However, as prev forecaster indicated, the main focus of the low level jet and best moisture transport lifts north into northern New Eng, and the upper jet dynamics do as well. This and speed of system will limit rainfall potential with most areas receiving less than 0.50" and likely less than 0.25" across SE New Eng. Heaviest rainfall will be across western New Eng closest to best forcing with amounts 0.50-1.00". Timing of rainfall 00-06z in the west and 06-12z in the east. Monday... Based on latest timing of the fropa, showers and sct t-storms should be exiting eastern MA by early Mon with deep layer drier air sweeping across the region from the west. It is possible the showers could be mostly east of the coast by 12z except for the Cape/islands. Expect increasing sunshine with gusty NW winds developing as modest cold advection develops. Max temps mostly mid to upper 70s with some lower 80s RI and SE MA and dewpoints falling through the 50s. Monday night through Tuesday night... High pres builds into the region providing cool and dry airmass with mostly clear skies and a touch of autumn as high pres builds into region. 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. Wednesday through Friday... Temps aloft moderate quickly with 850 mb temps approaching 15C by late Wed and increase further by Fri. This will result in temps recovering into the low/mid 80s Wed/Thu and possibly near 90 in spots by Fri. Comfortable humidity levels expected Wed/Thu but increasing humidity by Fri. High pres will maintain dry weather Wed/Thu, then next trof and approaching front may bring a few showers Fri.
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&& .AVIATION /20Z FRIDAY 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 Saturday Night/... Through 00Z...High confidence. SCT-BKN clouds around 5Kft across most of the region, except mainly clear along the immediate E coast. Light W-NW winds inland with light/variable winds across eastern interior areas. Sea breezes along the coasts should end by around 22Z-23Z. Clouds should begin to dissipate around 23Z or so. Tonight...Moderate confidence, mainly due to cloud cover. Mainly VFR through midnight, then areas of valley fog developing with MVFR- IFR VSBYS. May see area of low stratus move off the ocean as winds shift to SE after midnight with IFR-LIFR CIGS possible. Saturday...Moderate to high confidence. any areas of MVFR-IFR CIGS should improve to VFR by around mid day, though low clouds may linger across portions of interior Mass into early afternoon. Areas of fog should dissipate by mid morning, then VFR VSBYS. Sea breezes likely along the coast. Saturday night...Moderate confidence. Mainly VFR. May see IFR-LIFR CIGS move into central and western areas after midnight, along with patchy fog with MVFR-IFR VSBYS and a chance for showers. KBOS TAF...High confidence. Sea breeze should kick out by 22Z-23Z. KBDL TAF...High confidence in TAF. Outlook /Sunday through Wednesday/... Sunday...Moderate confidence. Areas of MVFR/IFR cigs and patchy fog may linger into Sun morning, then improving to VFR. Low risk of a few showers and an isold t-storm, mainly across western areas. 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. 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 Saturday Night/... High confidence. Winds and seas remain below small craft advisory thresholds as high pres builds across, then moves slightly south and east of the waters late tonight and Saturday. Outlook /Sunday through Wednesday/...Moderate confidence. Sunday...Quiet boating weather with S/SE winds 10-20 kt with mainly dry weather and good vsby. 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. 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...KJC NEAR TERM...EVT SHORT TERM...Doody LONG TERM...KJC AVIATION...KJC/EVT MARINE...KJC/Doody/EVT

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