Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 231911 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 311 PM EDT MON MAY 23 2016 .SYNOPSIS...
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* Updates to near- and short-term forecast portions only... An area of low pressure will wobble north along the coast into this evening and through Tuesday bringing with it showers and the chance of thunderstorms. Warmer weather follows beginning Wednesday. A weak front will move south of the region Wednesday night with dry, warm weather for Thursday. The front will move north toward southern New England as a warm front on Friday bringing scattered showers and thunderstorms. The front will continue to drift slowly north over the Memorial Day weekend.
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&& .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
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315 pm update... Cumulus continues to bubble with showers and thunderstorms emerging W/SW outside of New England within the more favorable region of low level convergence beneath mid level forcing per inverted elongated vortex energy parent to the Mid-Atlantic mid to upper level low. More on that later. Mesoanalysis has signaled a somewhat limited environment of instability to which some have noted in the office to be diminishing. Appearing more like the day will end up dry with highs ranging around the mid to upper 70s mainly across the interior with a few places topping out at or slightly above 80, but again can not rule out a spot shower over the CT River Valley. Anywhere well over the convective temperature of 76 per 12z Albany sounding yields an environment of considerable buoyancy given the lapse rates aloft. Can not call it finished just yet. Less threat along the coast as it remains cool with the onshore flow. Activity diminishes with sunset and temperatures drop. Attention then turns on the mature low over the Mid-Atlantic beginning to transition into its dying / occluding phase as it wobbles N. More on that in the tonight section below. Tonight... Unsettled, wet weather expected though variance within near-term high-res forecast guidance leaves a lot to be desired with respect to specifics. Taking a broader view, low pressure wobbles N evolving into its dying phase undergoing occlusion. Airstreams cyclonically trowal into the low center yielding a comma-head structure. During this morphology focus is on the crux of mid-level vortmax energy and parent weak low-level convergence rounding NW round the low into S New England. Should see decent low to mid level forcing, with some venting aloft, along the leading edge of which a band of light to moderate rain should emerge. Also possible embedded thunderstorms given marginal instability and weak shear parent to expected lift, but such activity should be non-severe with the main threats being lightning and heavy rain. So taken altogether likely PoPs would be warranted, but it`s unclear as to when and where specifically. A consensus of high-res and mos- guidance performed, confidence is for a band of activity to pivot NW across S New England settling N to S across W New England and along the high terrain. This keeps a good chunk of E/SE MA in chance PoPs. A moderate confidence forecast with mild conditions as low range around the mid 50s. Likely a mixed-bag of conditions consisting of mist and fog resulting in subsequent reductions in visibility.
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&& .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
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Tuesday... Breaking down. Low chokes itself off entraining drier air as it stacks and undergoes occlusion within its dying phase. The trowaling and comma shape to the low persists albeit weaker seemingly over W portions of New England parent with low level convergent flow along the E slopes of high terrain and forcing per rotating mid-level vortex energy. But to the E we could see some improvement with clouds becoming broken and perhaps some hints of sunshine. Thus can not rule out partial clearing. PoPs evolving with highest confidence over the Berkshires while chance-scattered to the E/SE if forecast models are right in the evolution of drier air wrapping into the system. A lot of wiggle room and wobble with this system to which the high-res guidance is not absolutely succinct but has a decent handle on the trend. Will avoid high PoPs accordingly with the scattered to broken nature of the low. Thunder does remain a possibility with continued marginal instability and weak shear. Think isolated chances and will prevail accordingly. Cooler day with clouds in abundance and E/NE flow. Highs up into the 60s. An edge warmer to the W as conditions improve late in the day with winds shifting out of the W/NW. Tuesday Night... The end. Low continues to undergo its dying phase choking upon drier air as it peels off to the E. Comma head over the W sweeps E across S New England per a consensus of high-res forecast trends, but by this point the activity is all but scattered. Should see most of the wet weather by consensus conclude by midnight behind which W/NW flow prevails. Anticipated clearing and light winds, would expect lows to drop into the 40s, and considering the recent rains, can not rule out some dense fog development if conditions are right.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/... Highlights... * Significantly warmer Wednesday and Thursday * Cooler on Friday with Scattered showers and thunderstorms * Warm for Memorial Day weekend with a few showers/thunderstorms Overview and Model Preferences... At upper levels...a persistent upper low moves northeast over the Canadian Maritimes by late Wednesday afternoon. A strong upper level ridge of high pressure will develop from the mid-Atlantic coast to New England late in the week and next weekend. At the surface...a weak front will slip south of the region Wed night bringing a wind shift to the north and drier air for Thu. That front will strengthen and move northward as a warm front by Fri...bringing increasing chances of showers and thunderstorms and cooler weather. The front will slowly edge northward next weekend allowing summerlike temperatures to return for the Memorial Day weekend but with a few showers and thunderstorms possible each day. Tuesday night... As the upper low finally moves northeast away from the region, any lingering light showers will end in the evening and skies will clear out after midnight. Lows mainly 50-55. Wednesday... Brief ridge of high pressure to our south takes over, leading to westerly downslope air flow, drier conditions, and more summer- like temperatures away from the coast...mainly 80 to 85.There could be seabreezes, but it appears the synoptic flow could be just strong enough to prevent lower temperatures along parts of the MA east coast. Cape Cod and the islands, as well as Cape Ann, however, will likely remain as cool as the south coast of New England, where southwest winds should prevail...upper 60s to mid 70s there. Wednesday night and Thursday... Weak low pressure passes by to our northeast Wed evening and an associated weak front will move across our region. The front will usher in very dry air aloft and light west winds will turn northerly. With a good deal of sunshine on Thu, high temperatures will again reach the 80 to 85 degree mark over the interior. But there will be a better chance of sea breezes along the entire east and southeast coastline, with temperatures only reaching mid 60s to mid 70s at the immediate coast. Thursday night and Friday... The front that moved through Wed night will strengthen to our south and begin to head northward Thu night. Winds will turn to the east and southeast, bringing an increase in moisture and a chance of showers and isolated thunderstorms later Thu night. Friday now looks like a much cooler day than earlier anticipated, with a warm front in our vicinity and a continuation of E to SE flow. It will be on the cloudy side with a chance of showers and thunderstorms, especially in western sections. Highs only in the 70s...cooler at the immediate coast. Saturday and Sunday... This far out...there is still a fair amount of uncertainty. However, it looks like the warm front will drift slowly northward on Saturday and be completely north of the region on Sunday. The Memorial Day weekend should feature a return of summer-like temperatures with highs in the mid 80s. Upper 80s are possible in the Connecticut River valley on Sunday. There is a possibility of scattered diurnally-driven afternoon and evening showers or thunderstorms, but most of the time it should be dry. && .AVIATION /19Z MONDAY THROUGH SATURDAY/...
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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 Night/... 18z update... Today...High Confidence. Mostly VFR. SHRA/TSRA potential over CT Valley terminals into this afternoon and towards evening to which could produce TEMPO MVFR/IFR. E/NE winds with gusts up around 15 kts. Tonight...Moderate Confidence. Specificity difficult to nail down. Will prevail VCSH with uncertainty while -RA with confidence. Anticipate scattered SHRA with chance TSRA with greater confidence of impact over W terminals. With respect to cigs and vsbys, confident widespread MVFR/IFR impacts with fog and mist especially over E/SE terminals. NE winds with gusts upward of 15 kts. Tuesday...Moderate Confidence. SHRA and chance TSRA continue with greatest confidence over W terminals. Widespread MVFR/IFR impacts begin to shift E with the usherance of winds backing out of the W/NW. Gusts of around 15 kts possible. Tuesday Night...Moderate confidence. Continued clearing trend W to E with W/NW winds. Improving to VFR. It is perhaps at the start of the period that MVFR/IFR will only linger along the E coast of MA. KBOS TAF...Wet weather likely to be either approaching or in the area during TAF periods of VCSH. -RA prevailed where there was greater confidence of rain impacting the terminal. -RA could become more widely scattered into Tuesday with much of the activity focused W. Can not rule out SCT-BKN cigs and TEMPO VFR before conditions clear out Tuesday evening. KBDL TAF...Confident the terminal will see a fair share of -RA beginning around midnight and continuing through much of Tuesday before clearing out late. There is the possibility of TSRA, in the vicinity to the N/W this afternoon, and again overnight. With the anticipated isolated nature, opted not to prevail TSRA. TAF will be amended accordingly should confidence increase and conditions warrant. Outlook /Wednesday through Saturday/... Tuesday night... Moderate confidence. Any lingering MVFR improving to VFR after midnight. Could be isolated IFR in patchy fog late. Wednesday through Thursday...High Confidence. VFR. Thursday night and Friday... Low to Moderate Confidence. Mainly VFR early Thu night...becoming MVFR with areas of IFR in showers and possible fog patches. Isolated thunderstorms late Thu night. Mainly MVFR throughout the region on Fri with scattered showers and thunderstorms. Isolated IFR possible in heavier showers or in patchy fog mainly near the coast.
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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. 315 pm update... Tonight and Tuesday...Moderate Confidence. Low pressure wobbles around S New England. E/NE winds with gusts up to 15 kts. Seas dropping below 5 feet early. Main concern is with anticipated wet weather that there will be reductions to visibility out on the waters. Can not rule out visibilities falling as low a a few miles with mist / fog. Tuesday Night...Moderate Confidence. Winds back out of the W/NW with departure of the low. Change in wind direction against a E/SE swell, could see some wave heights up to 5 feet on the outer waters requiring small craft advisories. Aside, rain comes to an end and visibilities improve if they had not done so during the day Tuesday. Outlook /Wednesday through Saturday/... Wednesday... Moderate Confidence. Seas subside into Wednesday afternoon. Light winds. Wednesday night and Thursday... Moderate confidence. Light winds from the southwest will shift to the northwest Wed night and to the northeast to east on Thu. Seas mainly well below small craft criteria...but could reach 5 feet over the waters southeast of Nantucket late Thu afternoon. Thursday night and Friday... Moderate confidence. Southeast winds on the order of 10-15 kt and seas 1 to 3 feet. Just a slight chance of showers or a thunderstorm.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 8 PM EDT this evening for ANZ250-254-255.
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&& $$ SYNOPSIS...Sipprell NEAR TERM...Sipprell SHORT TERM...Sipprell LONG TERM...GAF AVIATION...Sipprell/GAF MARINE...Sipprell/GAF

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