Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 232019 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 419 PM EDT MON MAY 23 2016 .SYNOPSIS...
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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/... 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. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... 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. && .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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HIGHLIGHTS... * Significantly warmer and dry Wednesday and Thursday * Above average temperatures will continue Friday into Sat * Hit or miss showers with thunderstorms are possible into the Holiday weekend. OVERVIEW... Large scale pattern is in agreement with both determinisic and ensemble guidance. Upper level low will move towards the Maritimes as Midwest ridge builds into the Northeast. This ridge will bring summer-like warmth and humidity to the region as ensembles show both the 700 and 500 heights nearly 1-2 standard deviations above normal. Several waves will move through the flow keeping a chance of showers and thunderstorms in the forecast for Late Thursday into Saturday. Because of the mesoscale differences in the guidance trended the forecast towards an overall blend. DAILIES... Wednesday into Thursday...Moderate Confidence. Upper level low will push towards the Maritimes on Wednesday. However, a quick moving shortwave will try to push through the region during the day. This approaching frontal system will slow down or stall as mid-level heights begin to build across the region. Therefor, believe that an isolated shower across the higher terrain is possible but most of the day appears to be dry. Good mixing during the afternoon will help warm temperatures back to above average with highs in the low to mid 80s. This may be the first time that Boston Logan will hit 80F. The cold front weakens and stalls over the region by Thursday as ridging aloft continues. There is the potential for a spot thunderstorm especially across the CT valley and points west where the better instability will occur. So another mainly dry day is anticipated on Thursday. Temperatures will be similar to that on Wednesday with mixing up to 800mb. Will be cooler along the coastlines as a sea breeze looks to develop during the afternoon. Thursday night into Friday...Moderate Confidence. Depending on where the front stalls, we could see scattered showers and thunderstorms Thursday night into Friday. Guidance continues to hint at the possibility of a decaying MCS moving from the Great Lakes region towards southern New England. However latest trends is that this will pass closer to NH than directly over southern New England. Something to watch in the coming days. Friday, it still remains unclear how far northward the front will make it. If it stalls/remains over the region then showers and thunderstorms may continue, keeping more clouds than sun which will lower temperatures. Right now believe that the front will get through a good portion of the area allowing for temps to reach into the 80s with mid to upper 70s across the east coast. Memorial Weekend...Moderate Confidence on Saturday. Low Confidence on Sunday. High pressure south of the region will begin to strengthen on Saturday. This will continue to build the ridge to 2-3 standard deviations above normal. Saturday looks quite balmy with 925 mb temps warming close to 21-23C. This could result in highs in the mid 80s on Saturday, with a low probability of a 90F across the CT valley. For now continue with a conservative route for temperatures. These warm temperatures and lingering moisture may trigger off afternoon convection on Saturday. Low confidence on Sunday as EC wants to push a backdoor cold front through the region where the GFS brings the front through on Monday. Depending on the frontal timing, temperatures on Sunday could be in the mid 80s with sun or the upper 60s with clouds and drizzle. Will have to wait for the guidance to come in better agreement before having a better idea on how the weekend will end for southern New England.
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&& .AVIATION /20Z 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/... Wednesday through Thursday...High Confidence. VFR. Thursday night and Friday... Low to Moderate Confidence. Mainly VFR...becoming MVFR. Showers and thunderstorms beginning late Thursday night lasting through Friday. Saturday...Moderate Confidence. Mainly VFR with some MVFR within in scattered shower or thunderstorm.
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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/...Moderate confidence. Wednesday...Seas subside into Wednesday afternoon. Light winds. Wednesday night and Thursday...Light winds from the southwest will shift to the northeast by Thu as a frontal system stalls over the waters. Seas mainly below small craft criteria but cannot rule out a few hours of 5 footers across the southeastern waters. Thursday night and Friday...Southeast winds on the order of 10-15 kt and seas 1 to 3 feet. Just a slight chance of showers or a thunderstorm. Saturday...Southwest winds will prevail with seas less than 3 feet.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 8 PM EDT this evening for ANZ250-254-255. && $$ SYNOPSIS...Dunten/Sipprell NEAR TERM...Sipprell SHORT TERM...Sipprell LONG TERM...Dunten AVIATION...Dunten/Sipprell MARINE...Dunten/Sipprell

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