Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 222003 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 403 PM EDT Sat Oct 22 2016 .SYNOPSIS... A strong upper level disturbance sweeping across New England will usher in colder air and blustery, potentially damaging-winds through Sunday. Wind advisories and gale warnings posted. Upper trough and possibly weak surface low pressure will pass south of New England Monday morning. Dry and cool northwest flow will persist Monday afternoon through Wednesday. High pressure will drifts east of New England late Thursday followed by a front and possible showers late Thursday night into Friday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... 4 pm update... */ Highlights... - Rain moving out, winds picking up quickly out of the W - Low pressure deepening, winds increase, temperatures drop - Gusts up to 50 mph possible Sunday - Wind Advisory in effect, event-driven with leafed trees */ Discussion... Through this evening... Negatively tilted trough continues to lift N/E across the region as a prominent dry slot wraps into the system. Along the leading edge, a well-defined line of moderate rain with embedded heavier showers pushing N, exiting over the next couple of hours. To the W, a dynamically driven environment of low to mid level QG forcing yielding an area of rain and a low risk of a rumble of thunder. This area will pivot N/E across S New England for the remainder of the afternoon, exiting out during the evening hours, lingering the longest across the high terrain. Colder air rushing in and numerous reports of snow accumulation across the high terrain well to the N/W over Upstate NY into VT / MA. Already reports of nearly an inch in Peru, MA as of 4 pm. Given the dynamic situation and likely many to be caught off guard with the first snow of the season, will go ahead with the issuance of a SPS for the high terrain along the E slopes of the Berkshires. Tonight... Blustery W winds with the possibility of wind-related damage. Wind Advisory for all of Southern New England. Surface low deepening to 980 mb as it lifts northeast through Maine. Tightening pressure gradient and isallobaric component. This as cold, dry air pushes across the region. Expect the shallow airmass to result in boundary layer mixing up to H9 throughout allowing the mix-down of faster momentum aloft, with the top of the mixed-layer blowing out of the W around 45 mph. While highest confidence of reaching wind advisory criteria is across the high terrain and along the immediate coast adjacent to warmer waters, the entire area is included given fully foliated trees and their susceptibility to potential impacts even with winds of 30 to 40 mph. Likely to see some down branches, trees, overall issues that will lead to isolated-scattered power outages. This as showers linger across the high terrain as the main comma- head vort-lobe associated with the negatively-tilted trough axis lifts N/E along with better QG-forcing and trowaling moisture. Do anticipate broken to overcast cloud decks to linger with cold air advection proceeding at the surface with milder, dry air aloft. Likely PoPs for the high terrain. Cold air advection pushes lows down into the upper 30s to low 40s. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday... Wind-related threats continue with the possibility of gusts up to 50 mph. Clouds clearing out allowing for abundant sunshine and boundary layer mixing up to H85 where forecast soundings suggest winds at the top of the mixed layer will be around 50 mph. Ensemble probabilities support a wind advisory threat over all of Southern New England with W gusts up to 45 mph, with highest confidence of strongest gusts over the high terrain and immediate coast adjacent to warmer waters. Question as to whether there is the additional threat of downsloping winds into river valleys given cold air within the low levels with H85 temperatures around -2C warming to 0C towards late in the day. Going to keep winds blustery throughout much of the day though the timing of greatest impacts looks to be around mid to late morning through early afternoon. Given temperatures aloft, looking at a cooler than average day with temperatures around the mid to upper 50s. Sunday night... Wet-weather expected overnight. Moistening low levels and increasing clouds associated with isentropic upslope of a continental-polar airmass along a leading warm-frontal boundary. This associated with mid-level forcing per stretched vort lobe through a broadly open- wave trough and accompanying reinforcing surface cold front. Looking at showery weather moving into S New England after midnight and into the Monday morning period. Could be a moderate W to E band parent to greatest forcing and low to mid level frontogenesis though. Tough to nail down but the consensus of forecast guidance and ensemble probs have the bulk of wet-weather activity S of the Mass Pike. Remaining mild with S winds. Lows forecast to fall down around the low to mid 40s. && .LONG TERM /MONDAY THROUGH SATURDAY/... */ Highlights... * Quick moving short wave trof and moisture plume brings chance of rain southern zones Mon morning * Series of cold nights Mon through Wed nights may trigger Frost/Freeze headlines for some zones not yet turned off * Potential rain event late Thursday night into Friday */ Overview... Trof over Labrador remains anchored in place for a time and then only slowly moves east over the North Atlantic. As a result, southern New England remains in NW flow with steady supply of cold air advecting into the region through at least mid week. There are a couple of short waves to keep an eye on during this period. One fast moving upper short wave trof with flat surface wave moves quickly along or just south of the New England south coast Monday AM. A second and higher amplitude short wave trof approaches the east coast Thursday night into Friday. Medium range deterministic models have come into better agreement for now and somewhat consistent with prior ensembles. Nevertheless, the time period is still 5 to 6 days out with energy still tracking across the Pacific. Hence, we may see varying depictions of how the energy is handled as we get closer to the end of the week. Some prior runs handled this energy differently due to split flow upstream. Probably a cool and dry regime going into the next weekend with early signals showing a tendency for one long wave trof to set up over the far eastern Pacific and another along or perhaps just east of the east coast. Details... Monday...Fast moving short wave energy rotating about the Labrador vortex may have enough going for it to reflect a very flat surface wave passing west to east just south of New England and deep enough moisture to support a period of light rain...most likely across RI and southeast MA. The south coast looks to be close to the left exit region of a H250 jet streak passing through the mid Atlantic region. At this time amounts look to be under a quarter inch. Since we do not have all that much continuity on this feature, will just indicate chance POPs for now. Clouds and rain could suppress temperatures a few degrees over the Cape and Islands. Monday night through Thursday...Looks dry and on the cool side during this period with NW flow persisting. May be enough decoupling Monday and Tuesday nights to allow temperatures to drop below freezing in many northern interior locations, although the more exposed areas may still experience some mixing. By Wednesday night, winds should be quite light over the area as surface high pressure drifts across the area, but the air mass will be starting to modify. Thursday night and Friday...Short wave trof energy will likely affect the area to at least some extent. Both the ECMWF and GFS deterministic models indicate what may be a cold occlusion with possible triple point moving across southern New England Friday morning, but those details are subject to change between now and then. At any rate, it seems prudent to depict chance POPs for that time frame. Temperature forecasts for Friday could be quite challenging with a high dependency on the timing of the system. Saturday...Looks to be dry and somewhat cool in a NW flow behind the departing surface front and upper short wave trof. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/... 20z update... Rest of Today... Improving to MVFR with TEMPO IFR CIGS and minor VSBY issues as an area of -RA/RA sweeps N/E across the terminals. Increasing W winds with gusts up around 35 to 40 kts possible, especially S/SE coastal terminals. Tonight...High confidence. MVFR cigs improving to VFR. SCT SHRA continuing, but becoming less, mainly N/W New England and focused over higher terrain. W wind gusts up to 40 kt with highest confidence over high terrain and coastal terminals. Sunday...High confidence. Clearing during the morning to VFR. W gusts around 30 to 40 kts during the day with strongest across the high terrain and coastal terminals where 45 kts is possible. Sunday night...Moderate confidence. W winds taper into evening. Will see increasing low-end VFR to MVFR cigs towards midnight and into morning associated with an area of -RA/RA. Impacts mainly focused along and S of the Mass Pike. KBOS TAF...Winds on the increase S/W of the terminal and expect such momentum to work into the terminal over the next hour or so. Can not rule out winds in excess of 40 kts overnight, but the lack of confidence as to when, will hold off on the issuance of an Airport Weather Warning at this time. KBDL TAF...While breezy tonight, the stronger winds will be across the terminal on Sunday. Some concern during the overnight period that should the winds remain light there could be an issue of LLWS as winds 2 kft agl tonight will be out of the W around 35 to 40 kts. Outlook /Monday through Thursday/...High confidence. Monday...VFR except possibly MVFR cigs/vsbys in light rain and fog during the morning along the south coast. Tuesday through Thursday...VFR. NW wind gusts to 25 knots still possible during Tuesday. Thursday night into Friday...Areas of IFR to MVFR cigs/vsbys in showers and areas of fog possible. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Sunday Night/...High confidence. 4 pm update... Tonight... A strong burst of winds out of the W/SW the last couple of hours with gusts up to 45 kts associated with faster momentum moving into the region and mixing down to the surface. Expect a general trend over all waters overnight of wind gusts around 35 kts, as high as 40 kts. Gale warnings ongoing. Seas becoming rough with the enhanced wind stress. Visibilities improving with increasing winds. Sunday... Gale force W winds continue with gusts up to 45 kts possible. Seas remaining rough building upwards of 10+ feet on the outer waters. Gale warnings continue. Sunday night... Gales taper and will see the conclusion of Gale Warnings as we go through the period. Will also see an area of rain sweep the S waters towards midnight and continue into the morning hours. Seas remain rough due to the wind stress. Likely see Gale Warnings converted to Small Craft Advisories. Outlook /Monday through Friday/... Through Thursday...High confidence. Small Craft NW wind gusts may persist over most of the waters through Tuesday. Quieter conditions anticipated for Wednesday through Thursday. Friday...Moderate confidence. Some uncertainty exists with the evolution of a weather system for Friday, but it has the potential to have enough of a pressure gradient to support wind gusts near the Small Craft Advisory threshold of 25 knots. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Wind Advisory until 2 PM EDT Sunday for CTZ002>004. MA...Wind Advisory until 6 PM EDT Sunday for MAZ002>024-026. RI...Wind Advisory until 6 PM EDT Sunday for RIZ001>008. MARINE...Gale Warning until 2 AM EDT Monday for ANZ231>234-251-255-256. Gale Warning until 11 PM EDT Sunday for ANZ230-235>237. Gale Warning until 5 AM EDT Monday for ANZ250-254. && $$ SYNOPSIS...Sipprell/Thompson NEAR TERM...Sipprell SHORT TERM...Sipprell LONG TERM...Thompson AVIATION...Sipprell/Thompson MARINE...Sipprell/Thompson is the U.S. government's official web portal to all federal, state and local government web resources and services.