Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 201408 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1008 AM EDT MON JUN 20 2016 .SYNOPSIS... Not much change from the past several days, as a high pressure remains in control. Humidity increases, with a chance of showers and thunderstorms, ahead of a cold front tonight into Tuesday. Seasonable temperatures through the work week. A low pressure passes to the south late Thursday, with high pressure then building back in for the end of this week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1015 AM Update... No major changes to the forecast at this time. Still watching some high level cirrus moving across the region this morning. Low level stratus has officially burned off, but something that could redevelop tonight. Did adjust wind speed up a bit as a few locations are already gusting to 15 kts. Otherwise forecast is on track for today as temperatures will continue to climb into the mid to upper 80s away from the south coast. A few spots may hit 90s, depending on cloud cover. Previous Discussion... Primary changes this morning were to bring skies more in line with current trends. Area of stratus has formed in CT and snaked up the CT valley over the last couple of hours. This is a very thin deck, so with mixing already ongoing, should see this dissipate by about 10AM or so at the latest. NAMDNG only guidance handling this well at all, so skies are tailored toward it`s solution. Did make some minor adjustments to the southern sections of the CT valley, which will be slower to warm because of this stratus. Peak warmth today in the upper CT valley and Merrimack valleys.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... A cold front will move into southern New England tonight, then move offshore Tuesday. 20/00z guidance continues the trend of a faster timing for this frontal passage. With the timing still changing, have only moderate confidence in that aspect of this forecast. With the most likely timing being late tonight into Tuesday morning, there is not a lot of opportunity to generate instability. There are some dynamics to support thunderstorms. With a climatologically unfavorable time, thinking any thunderstorms will be isolated at best. Should a slower front timing actually occur, then the coverage and intensity of thunderstorms and showers would most likely increase. Tuesday will also start off a bit muggy, with dewpoints rising to around 60 degrees. However, expecting more drier air to arrive from the west for the afternoon hours. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... HIGHLIGHTS... * Chance for showers across the South Coast late Thursday from passing coastal Low * Cooler and less muggy conditions through most of the week into Sat Overview and model preferences... Longwave trof will gradually deepen and dig connected vortex centered just south of Ungava Bay. Little change expected as this trof will lie blocked between high pres center stalled across the SW CONUS and strong blocking ridging just to the E. This trof defines the wx, keeping temps near normal through much of the end of the week. It also acts as a conduit for secondary shortwave energy, which will trigger low pres development along a stalled frontal boundary to the S. How close this front lies will ultimately define how much of an impact is seen across Srn New England on Thu. Ensembles showing less spread with the 20.00Z runs, closer to the 40/70 benchmark. Therefore, will continue to lean closer to a blend of ensemble means as a baseline for the forecast, which follows the forecast from the last few days. Details... Tue night into Wed night... Trof continues to settle across the northeast with H5 temps dropping below -15C and strong cyclonic flow. This will lead to a continuation of cloud cover and even a few diurnally driven shra on Wed especially across the nrn tier, closer to the core of cold air aloft. Some TS and even small hail not out of the question with mid-upper temps this low. H85 temps only drop to around +10C so this with a combination of the mixed cloud, expect highs to still reach into the upper 70s and low 80s thanks to some breezy downsloping flow. Thu and Thu night... Cold frontal boundary which moves through on Tue will stall S of the region as it becomes parallel to the flow on the cyclonic shear side of the mean trof. A second shortwave, currently wrapped in the PACNW vortex will be entering this flow and is expected to be catalyst for cyclogenesis of the mid Atlantic along this stalled frontal boundary. The ultimate state of this front and passage of the frontal wave will determine how much if any impact is felt in Srn New England. Current ensembles bring it close to the benchmark. Precip shield likely thanks to connection to sub- tropical moisture. Will maintain the slight to chance pops as suggested by the ensemble blend, highest to the S. Temps, mainly near the low 70s with lows falling into the 60s. Fri into the weekend... Shortwave moves E allowing longwave trof base to shift E as well. Zonal flow expected across all of the NRN CONUS. With slight ridging upstream another round of high pres will gradually take control after what remnants of the offshore low pres move out to sea. Temps begin near normal, but then show signs of increasing as high pres shifts E, allowing return flow. More hot/humid wx possible by the late weekend. && .AVIATION /14Z MONDAY 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 Tuesday/... Today...High confidence. VFR dominates the rest of the day. Southerly flow should limit sea breezes on east coast. Tonight...Moderate confidence. VFR cigs developing after midnight and continuing towards morning, with scattered showers and isolated thunderstorms. Lower confidence for thunderstorms. Continued S winds around 10 kt. Tuesday...Moderate confidence. Mainly VFR conditions. Scattered showers with isolated thunderstorms during the morning may result in brief periods of MVFR conditions. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Tuesday Night through Friday/... Tue night into Wed...High confidence. VFR. Wed night into Thu...Moderate confidence. MVFR/IFR possible especially south of the Mass Pike as low pres moves across the S coastal waters. Fri...High confidence. Mainly VFR.
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&& .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday/...High confidence in trends. Moderate confidence in timing late tonight into Tuesday. Good boating weather overall, though there is the potential for hazards for small boats. S winds continuing with the likelihood of gusts up to around 20 kts. With tidal influence, waves are expected to be choppy at times across the nearshore waters, and up to 5 feet on the outer waters, especially across the outer coastal waters Tuesday. There`s a chance of wet weather late tonight into Tuesday. Drying conditions should occur Tuesday afternoon, although that timing is not certain. Low risk of thunderstorms late tonight into Tuesday morning. Increasing south winds ahead of a cold front should lead to rough seas across the outer coastal waters. Outlook /Tuesday Night through Friday/... Tue night into Wed night...Moderate confidence. Winds shift from SW to W-NW early Wed. Although gusts are likely to remain below small craft thresholds, seas 5-6 ft will linger into Wed night, so hazardous seas will remain an issue. Thu and Fri...Moderate confidence. Winds shift from W to E-SE late Thu into Fri. Once again winds should generally remain below small craft thresholds, but there is a risk for building seas (especially the southern waters) as low pres passes to the south. Small craft advisories may still be needed. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 PM this evening to 6 PM EDT Tuesday for ANZ250. Small Craft Advisory from 3 AM to 6 PM EDT Tuesday for ANZ254>256. && $$ SYNOPSIS...Belk/Doody NEAR TERM...Doody/Dunten SHORT TERM...Belk LONG TERM...Doody AVIATION...Belk/Doody MARINE...Belk/Doody is the U.S. government's official web portal to all federal, state and local government web resources and services.