Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 280306 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1106 PM EDT Tue Sep 27 2016 .SYNOPSIS... A front will stall just south of New England keeping the threat of showers over Cape Cod and especially the Islands through tonight. A cool and unsettled pattern will persist into the weekend, before slow improvement early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... 1040 PM Update... An area of showers continues to linger near and south of Nantucket and across the south coastal waters at 02Z. Also noting spotty reports of drizzle across E Mass including at KBOX. As E-NE winds freshen overnight, will likely see more reports of scattered showers and areas of drizzle across eastern areas. This is in line with the previous forecast. Temps at 02Z running mainly in the 50s, though a few lower-mid 60s linger across south coastal areas as well as the Worcester hills. Have updated overnight forecast to bring conditions current and incorporated trends. Previous Discussion... Frontal boundary and assocd deep moisture axis just south of New England and with upper level flow backing slightly tonight, the front and moisture will remain in place for most of the night before pushing south late as sfc ridging noses down from the north. Models indicate decent mid level omega south of New Eng in response to the convergence and right entrance region of upper jet which will result in showers continuing tonight for Nantucket. There is a fairly tight moisture gradient to the north which should keep focus for rainfall over Nantucket, but may see a few showers extend into Cape Cod and MVY. Rest of SNE should be dry, however there is a good set up for low clouds and areas of drizzle developing late tonight as low level moisture expands south within increasing low level NE flow and dry air aloft. Light winds will become NE late tonight. Lows temps will remain mostly in the 50s && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... Wednesday into Wednesday night... Upper level low digs south from the Great Lakes which will result in shortwave ridging aloft over New Eng. This will maintain surface ridging across the region from strong high pres over the Maritimes. Synoptic forcing is weak which should limit shower activity except perhaps across SE New Eng during Wed where deeper moisture axis remains. Showers approaching from the SW Wed night should remain to the west. Otherwise, increasing NE flow and abundant low level moisture below dry air aloft will result in patchy drizzle at times Wed into Wed night with widespread low clouds. A cool raw day and night in SNE with gusty NE winds to 30 mph along the coast. Highs Wed will be 60 to 65 degrees but only upper 50s northern MA as wedge of low level cooler air noses down from the north. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Highlights... * Onshore flow brings cooler/wetter pattern through Saturday * Slow drying early next week * Keeping an eye on the tropics Details... Uncertainty remains high through weekend as we deal with cutoff low moving through Ohio Valley and eventually across New England. While 12z models and their ensembles have come into better agreement with its position and eventual track, the models often struggle with details regarding timing of individual short waves around closed low which affects how much rainfall we will eventually see. Relying heavily on ensembles as opposed to individual model runs to help iron out uncertainty and run-to-run differences. GEFS and EPS probabilities both indicate greater potential for heavier rainfall well to our southwest across mid Atlantic region where better jet dynamics come into play as seen on 850/250 mb wind anomalies. Presence of downstream ridging over New England combined with persistent NE flow favors periods of rain/drizzle and patchy fog, though forecast will indicate showers to help convey it won`t be raining all of the time. Does look like a period of steadier rainfall will take place late Thu night into Fri and again late Fri night into Sat as a couple of short waves rotate across region, so bumped PoPs up to reflect this trend. Drier air begins to work into region Sat night and especially Sun as cutoff low heads to eastern Great Lakes, before it weakens as tracks across southern New England Mon along with surface cold front. High pressure builds into Northeast for midweek. Beyond that, still way too early to say much on Invest 97L. We`re sure many folks have seen longer range track guidance but we need to caution against jumping on any one particular solution. Our advice is to stay aware and informed over the next several days. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/... High confidence on trends and overall theme. Lower confidence on exact details. Overnight...MVFR-IFR CIGS/VSBYS across Cape Cod and the islands will eventually expand inland from east to west across eastern and central areas with patchy fog developing. CT valley will be last to see lower clouds around 06Z-07Z. Occasional showers will persist across ACK tonight with areas of drizzle developing elsewhere. Wednesday and Wednesday night...Widespread MVFR cigs likely with pockets of IFR possible. Areas of drizzle. NE wind gusts to 25 kt developing along the coast. KBOS TAF...Overall high confidence in TAF. Expect IFR cigs developing later tonight into Wed with slight improvement possible Wed afternoon. KBDL TAF...Moderate confidence in TAF. Mainly MVFR cigs developing late tonight into Wed. Outlook /Thursday through Sunday/...Moderate confidence. Thursday Through Saturday...Periods of MVFR/IFR in areas of drizzle and fog and possibly scattered heavier showers, especially near coast. NE winds with gusts up to 30 kts at times. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/...High confidence. Overnight...SCAs issued across the southern waters through the overnight across the southern waters with seas up to around 7 ft mainly across the southern outer waters in easterly swells. Light E-NE will increase across the NE Mass waters during the early morning hours then shifting S through daybreak. Expect reduced vsbys with scattered showers and patchy fog, mainly SE waters. Wednesday and Wednesday night...Increasing NE winds with gusts 25-30 kt developing, strongest on the eastern waters. SCA for all waters. Seas building up to 7-9 ft eastern waters. Patchy drizzle and fog will reduce vsbys at times. Outlook /Thursday through Sunday/...Moderate confidence. Small Craft Advisory conditions likely through at least Saturday due to persistent NE flow. Gusts could reach Gale force at times, especially later Thu night and Fri. As a result, seas should build to 8 to 10 ft offshore, possibly up to 12 ft. Also expect areas of drizzle and fog with scattered heavier showers, reducing visibility to around 1 NM at times. Winds diminish later Sat into Sun but seas offshore should take longer to subside. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 8 AM Wednesday to 8 AM EDT Thursday for ANZ230>237. Small Craft Advisory from 5 AM Wednesday to 8 AM EDT Thursday for ANZ250-251. Small Craft Advisory until 8 AM EDT Thursday for ANZ254. Small Craft Advisory until 8 AM EDT Thursday for ANZ255-256. && $$ SYNOPSIS...KJC/EVT/JWD NEAR TERM...RLG/EVT SHORT TERM...KJC/EVT LONG TERM...JWD AVIATION...KJC/RLG/EVT MARINE...KJC/EVT/JWD is the U.S. government's official web portal to all federal, state and local government web resources and services.