Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 210110 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 910 PM EDT Sat May 20 2017 .SYNOPSIS... A beautiful day to close out the weekend will be followed by cool and wet weather on Monday. Dry and seasonable weather expected Tuesday, but unsettled weather returns Wednesday through Friday with some showers at times. A drier trend in the weather may finally arrive by next weekend. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/...
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910 PM update... Clear skies, light winds and a relatively dry airmass in place will allow for a chilly night with good radiational cooling. The normally colder locations of N central and interior E Mass as well as Martha`s Vineyard will likely see temps fall back to the mid and upper 30s. Some patchy frost may develop in those locations as well, though not widespread enough to issue a frost advisory at this point. Elsewhere, temps will fall back to the lower-mid 40s. Some high clouds may start to work into the CT valley after midnight.
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&& .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Sunday... Weak high pressure will break away from the ridge out of Quebec and settle in across the region through the day. Will see a lot of sunshine, though some high thin clouds may push in from W-E during the day. With a continued light pressure gradient, expect light and variable winds. Sea breezes will develop along the coast. Expect temps to only reach the upper 50s to lower 60s along the immediate coast, ranging to around 70 inland. Sunday night... The weak high will shift off the coast Sunday evening. Winds will shift to SE-S but remain light. Low pressure will push across the western Great Lakes, while its associated cold front will move across the Ohio Valley into western NY/PA. The leading edge of the moisture will approach the E slopes of the Berkshires and the CT valley around or after midnight. Scattered showers could push into central and western areas, though expect light rain amounts on the leading edge of the precip. Temps will only fall back to the mid 40s to near 50. && .LONG TERM /MONDAY THROUGH SATURDAY/... Highlights... * Periods of rain and unseasonably cool Mon/Mon evening * Dry weather returns Tue with seasonable temps * Some showers at times Wed through Fri but timing uncertain * Drier trend likely be next weekend Details... Monday and Monday night... Southwest flow aloft will push a shortwave and associated surface low pressure into the northeast. Modest southerly low level jet will develop along with a decent Pwat axis. Timing still uncertain, but forcing for ascent should increase allowing rain to overspread the region from west to east Monday morning. A secondary low pressure system should develop near the south coast and may result in a period of briefly heavier rain Monday afternoon into early evening, but flooding is not expected. There also is a low risk of a rumble or two of thunder, but certainly not expecting anything widespread. Onshore flow, clouds and rain will result in an unseasonably cool day with highs mainly in the 50s. Patchy fog may also develop especially later Mon into Mon night. Tuesday... Wave of low pressure departs so lingering low clouds should exit the region from west to east allowing partly to mostly sunny skies by afternoon. The one fly in the ointment is along the coast, especially the Cape and Islands where low clouds may linger longer than the models suggest. High temps will probably recover well into the 70s away from the coast given the strong late May sun angle, but weak gradient may allow for cooler sea breezes on the coast. Wednesday through Friday... Active weather pattern as deep anomalous closed upper level low drops south over the midwest. The result will be south to southwest flow aloft across southern New England. This will transport deep layer moisture northward along with several pieces of shortwave energy. Specific timing uncertain, but periods of showers likely at times Wed/Thu and into Fri. While the entire period will not be a washout, seems reasonable for several rounds of showers given the setup. The overall thunder risk is probably low Wed/Thu, but perhaps a better chance by Fri as upper low/cold pool aloft may be in the vicinity of southern New England. Temps Wed through Fri are uncertain and will depend on timing of precipitation and wind direction, but they should mainly be in the 60s to lower 70s. Deep moisture in place should result in dewpoints at least in the 50s, so low temps will almost certainly average above normal. Saturday... Low confidence in this time range but appears upper trough will be lifting to our northeast. This may result in a tendency for drier weather, although a few showers can certainly not be ruled out at this point, especially if upper trough is slower to depart. Highs probably in the 60s to lower 70s. && .AVIATION /01Z SUNDAY THROUGH THURSDAY/...
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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 Sunday Night/... Tonight...High confidence. VFR. Light/variable winds. Clear skies through midnight, then high thin clouds move into western areas. Sunday...High confidence. VFR. High clouds move in from W-E during the afternoon. Light N-NE winds early, shifting to E-SE up to around 10 kt along the S coast. Sea breezes likely along the immediate coast. Sunday night...Moderate confidence. VFR to start, lowering to MVFR from W-E in developing -SHRA, with IFR CIGS/VSBYS possible after 08Z-09Z. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Monday through Thursday/... Monday into Monday night...Moderate confidence in MVFR to IFR conditions in periods of rain with some patchy fog. Modest LLWS possible late Mon/Mon evening across the southeast New England coast along with the low risk for an embedded t-storm or two. Tuesday...Moderate to high confidence. Any lingering low cigs/vsbys across southeast New England should improve by late morning or early afternoon. Otherwise, VFR conditions. Wednesday and Thursday...Low to moderate confidence. Periods of MVFR to IFR conditions likely in rounds of showers, low clouds and fog. However, specific timing is quite uncertain.
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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 Sunday Night/...High confidence. Tonight and Sunday... Expect light/variable winds tonight. On Sunday, light E-NE winds to shift to SE during the afternoon. Sea breezes developing along the shoreline. Seas 4 ft or less. Sunday night...S-SE winds up to around 10 kt with light seas. Some showers may approach the waters from W-E mainly after midnight. Outlook /Monday through Thursday/... Monday and Monday night...Moderate confidence. Modest southerly low level jet should result in a period of southerly wind 20 to 25 knots Mon afternoon and evening. Marginal 5 foot seas are also anticipated on the southern waters along with patchy fog and even the low risk for an embedded t-storm or two. Small craft headlines will likely needed for some of our waters. Tuesday...Moderate to high confidence. Weak pressure gradient should keep winds and seas below small craft advisory thresholds. Wednesday and Thursday...Moderate confidence. Persistent southerly flow of 10 to 15 knots with occasional gusts between 20 and 25 knots anticipated over this time. Marginal small craft conditions at times, especially across the southern waters where long southerly fetch will build seas to between 4 and 6 feet Wed into Thu in those locales. Periods of showers along with areas of fog will also reduce visibilities for mariners at times. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Frank/EVT NEAR TERM...KJC/EVT SHORT TERM...EVT LONG TERM...Frank AVIATION...Frank/EVT MARINE...Frank/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.