Area Forecast Discussion
Issued by NWS Boston, MA

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564 FXUS61 KBOX 220236 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1036 PM EDT SAT MAY 21 2016 .SYNOPSIS... Mid-Atlantic low pressure moves up the coast overnight, passing southeast of New England into the Gulf of Maine for Sunday. A return of cooler conditions with wet weather mainly confined to E/SE portions of New England. A second low pressure brings more scattered showers Monday into Tuesday. A warming trend begins Wednesday, with showers diminishing. A front lingers just to our north late next week. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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Rain is moving across the islands and Cape Cod. Also an area of showers moving into Western MA/CT. Trends continue to support forecast of rain/showers moving into Southern New England during the night. Meanwhile, dew point depressions of 10-15 degrees will limit rainfall in the interior sections of our region. No significant changes to this forecast.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday into Sunday night... Continued low maturation into the Gulf of ME as a cold front pushes S into the NE CONUS. Two separate airmasses between which sinking air and dry weather prevails. While forcing parent to the Gulf of ME low is far removed from New England, cold and dry conveyor belt motions prevail. It is anticipated that across interior New England it will remain quiet with dry conveyor belt motions, while over E New England it remain socked in with the threat of drizzle / light showers. Along with NE flow, looks to be cool and dreary. To the W, cold pool associated with the broad troughing pattern yields an unstable profile ahead of the diffuse weakening cold front. With any sunshine a diurnal storm pattern emerges. But emphasize some wiggle room considering the difficulty already as to which the forecast models are having with the present synoptic situation. This warrants a look at ensemble probabalistic forecasts. Such wiggle room can alter the balance in airmasses in New England with a more unstable environment to the W and a dreary environment to the E. In-between prevailing dry with sinking air. Can not rule out such a shift in activity either E or W. So a cautious forecast that is not concrete. A model blend preferred with equal weighting to a MOS consensus. Does appear a SW-NE line across interior New England has the best chance of remaining fairly dry in comparison to other areas along the immediate W and E. Quiet over most of S New England overnight with only issues across E/SE with continued anticipated cold conveyor belt motions with the initial low dissipating and another redeveloping off the Mid- Atlantic parent with a mid-upper level cutoff low invoked by N- stream energy diving S. Looking at continued drizzle / light showers for E/SE New England and overall cool conditions. && .LONG TERM /MONDAY THROUGH SATURDAY/... Highlights... * Unstable and wet, but milder, Monday and Tuesday. * Warmer still, and drier Wednesday * Warmer still late week, but potentially unsettled. Overview and Model Preferences... Still looking at an amplified pattern, with our region beneath an anomalous cutoff through early next week. A strong downstream blocking ridge should shift east just enough mid week to permit this cutoff to eventually dissipate toward the end of next week. As it does, we get into more of a zonal mid level flow, which should stall a frontal boundary just to our north late next week. As usual with these patterns, models are in very good overall agreement with the trends and evolution. The portion of the forecast most likely to be an issue will be the timing. Will favor a consensus approach to smooth over some of these timing differences, which are more pronounced late next week. Details... Monday into Tuesday... Core of the upper level cold pool moves over southern New England, especially Monday night into Tuesday. In addition, a second surface low pressure should move into our region Monday night into Tuesday. This will mean another period of clouds, along with some showers. Timing-wise, expecting most of these showers to arrive from the south late Monday afternoon, peak Tuesday morning, then gradually move away Tuesday evening. This timing could change with later forecasts. Isolated thunderstorms are possible, despite modest CAPE values less than 500 J/kg. This is just due to the strength of the cold pool aloft. With fewer clouds to start, temperatures should be a bit higher Monday, then fall lower heading into Tuesday beneath the cold pool core. Wednesday... Brief ridge of high pressure to our south takes over, leading to drier conditions and more summer-like temperatures. Will have to consider seabreeze potential some more. At this point, it appears the synoptic flow should be just strong enough to prevent lower temperatures along most of the east coast of MA. Cape Cod and the islands, as well as Cape Ann, will likely not share in as much warmth. Thursday through Saturday... Warm front shifts into Canada and northern New England with return flow and ridging, Thursday. This front looks like it will get stalled just to our north late next week, due to the nearly zonal flow aloft. Looks like a good warm sector setup, with potential destabilization possible. The question will be available moisture. Thinking diurnally-driven showers and thunderstorms are possible, and will feature rainfall chances as such, especially Friday into Saturday across the western half of southern New England. Summer-like temperatures should continue. && .AVIATION /03Z SUNDAY 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/... Tonight...Moderate Confidence. Timing and the northward extent of rainfall remain the greatest uncertainties in the forecast. Approaching offshore storm system. Risk of -RA across S/SE terminals increasing, with deteriorating conditions to MVFR expected later this evening. S winds backing NE and increasing, with gusts up to 20 kts by morning. Sunday...Moderate Confidence. Continued optimistic forecast. MVFR over E/SE coastal New England with -DZ/-SHRA. VFR across the interior. Low risk of TSRA across W CT River Valley. E/NE flow, with gusts up to 30 kts especially over SE New England, Cape Cod, and Islands. Sunday Night...Moderate Confidence. MVFR over E/SE Coastal New England but E/NE winds diminishing. VFR elsewhere. KBOS TAF...Sea-breeze eroding out over the next hour or two, then winds turn variable for a time out of the S prior to backing out of the NE overnight and increasing towards morning. Will keep with an optimistic forecast keeping both -RA and MVFR mainly out of the terminal until Sunday morning. KBDL TAF...Optimistic forecast with keeping -RA and MVFR out of the terminal. Confident this will be the case through the TAF forecast. Outlook...Monday into Wednesday. Monday into Tuesday...Moderate Confidence. Although not a complete washout, periods of showers will continue across the area with northeasterly flow. This also suggests low clouds. Therefore, periods of MVFR/IFR are likely, but it`s possible occasional VFR, especially across the interior, will occur. Wednesday...High Confidence. Mainly VFR with high pressure. Thursday...Moderate Confidence. Mainly VFR. Scattered MVFR in showers possible, mainly west of KLWM-KORH-KIJD. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through Sunday Night...High Confidence. Low off the Mid-Atlantic / Delmarva lifts NE past the 40N/70W benchmark tonight into the Gulf of ME Sunday and Sunday Night. Will see an increase in areal coverage of rain and reductions in visibility down to roughly 3 to 5 miles starting this evening and continuing through Sunday Night. In addition to the low passage will see NE winds increase with gusts up to 30 kts and waves building to 6 to 8 feet. Low risk of gales so will continue with Small Craft Advisories. Outlook /Monday through Thursday/... Monday...High confidence. North winds will diminish and shift northeast to east. While remaining less that 25 kt, rough seas will linger across the eastern coastal waters. Will likely still need small craft advisories for some of the waters. Tuesday...Moderate Confidence. Winds still remain below 25 kt, but a second approaching low pressure will allow for building southerly swell. Small craft advisories may need to continue for some waters. Wednesday into Thursday...High Confidence. High pres briefly builds over the waters, mainly quiet boating weather expected. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 5 AM to 11 PM EDT Sunday for ANZ232>234. Small Craft Advisory from 5 AM Sunday to 8 AM EDT Monday for ANZ231-250-251-254. Small Craft Advisory from 2 AM Sunday to 5 AM EDT Monday for ANZ235-237. Small Craft Advisory from 2 AM Sunday to 8 AM EDT Monday for ANZ255-256. && $$ SYNOPSIS...Belk/Sipprell NEAR TERM...WTB/Belk/Sipprell SHORT TERM...Sipprell LONG TERM...Belk AVIATION...Belk/Sipprell MARINE...Belk/Sipprell

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