Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 200220 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1020 PM EDT FRI AUG 19 2016 .SYNOPSIS... 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. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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1020 pm update... High pressure will slowly move east of the region overnight. This will allow for a very light low level southeast flow. In response, we may see some spotty low clouds/fog patches develop after midnight but overall confidence in this remains uncertain as moisture is marginal. Highest risk for this will be across western/central MA and northern CT. Mainly dry weather expected overnight, but a spot shower or two is possible mainly in our southern zones. Low temps will bottom out mainly in the upper 50s to middle 60s by daybreak.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Saturday... H5 ridge builds across New England Saturday morning, then will slowly shift E during the afternoon. The surface ridge will also shift offshore, with S-SE winds in place through the day. Cloudiness will increase during the afternoon away from the coast. With residual subsidence in place, should remain dry for most of the day, though some isolated showers may sneak into western and central New Eng during the afternoon within the developing low level theta-e ridge axis. With the cooler temps early Saturday morning, agree with previous thinking that highs will be a bit lower than today`s. Expect readings to reach the lower-mid 80s for most areas, but holding in the mid-upper 70s along the immediate S coast, Cape Cod and the islands. Saturday night... Big question during this timeframe will be the amount of low level moisture that will move in across mainly central and western areas as an H5 trough moves slowly across the Great Lakes, bringing the flow aloft to a more S-SW direction. At this point, looks like bulk of the moisture should remain W of the region through the night, but can not rule out isolated showers pushing across the CT valley during the pre dawn hours. Have put in slight chance POPs mainly across the E slopes of the Berkshires. Expect overnight low to be cooler across interior E Mass (in the lower 60s) with readings a bit milder over the CT valley (65 to 70). It will be mild along the S coast as well, with temps only bottoming out in the 65-70 degree range. May see more patchy fog developing as well. && .LONG TERM /SUNDAY THROUGH FRIDAY/... 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. && .AVIATION /01Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/... Tonight...Moderate confidence, mainly due to cloud cover and cig heights. Mainly VFR through midnight, then areas of valley fog developing with MVFR-IFR VSBYS. May see area of stratus develop in the CT valley 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. A few showers possible central and W New Eng. 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 will shift to S by 02Z but redevelop Sat. 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. && .MARINE... 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 through the period. Winds and seas remain below small craft criteria with high pressure ridge across the waters tonight, then slowly shifting south and east Saturday and Saturday night. 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. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...KJC/EVT NEAR TERM...Frank SHORT TERM...EVT LONG TERM...KJC AVIATION...KJC/EVT MARINE...KJC/EVT

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