Area Forecast Discussion
Issued by NWS Boston, MA

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454 FXUS61 KBOX 231459 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1059 AM EDT Mon Oct 23 2017 .SYNOPSIS...
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High pressure offshore will provide mild temperatures today but also increasing humidity. A slow moving cold front will bring rounds of heavy rain Tuesday into Wednesday with a period of strong to damaging wind gusts possible. A few lingering showers are possible Thursday, but the trend towards drier, less humid and more seasonable temperatures are expected Thursday into Friday. Above normal temperatures may return by this weekend.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1025 AM Update... Patchy dense fog lingers across portions of the region, though not as organized as it was earlier this morning so allowed the Dense Fog Advisory to expire. Low clouds also linger across most of the interior, though noting breaks in the clouds across portions of the CT valley and across coastal SE RI and S Mass including Cape Cod and the islands on the latest GOES-16 (prelim, non-operational) satellite imagery. Seems the light wind field across eastern areas holding from the SE, which appears to keep the low visibility going into early this afternoon before briefly lifting through the remainder of the day. Still some question as to whether any scattered showers will develop across portions of the CT valley later this afternoon. Noting some differences in model solutions for later this afternoon/evening as to whether there will be enough low level lift and instability for any showers to develop there. Have kept slight chance POPs mainly for the E slopes of the Berkshires after 18Z or so, which might slip toward the Springfield/Hartford areas later today. As the winds slowly veer to S during the remainder of the day, will see temps slowly rise even with the cloud cover. Have kept max temps in the mid-upper 60s across the interior higher terrain to the lower 70s elsewhere. Have updated forecast to incorporate current trends through the remainder of the day. Previous Discussion... As the visibility slowly improves, lower clouds will linger a while longer. This will mean somewhat lower max temperatures, but still well above normal for mid/late October. Much of today should remain dry, but cannot completely dismiss the possibility of a few showers reaching western MA and portions of CT late today.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... Precipitable water increases tonight into Tuesday. Widespread showers arrive along a cold front late tonight into Tuesday, especially from Worcester county west. Strong winds of 35-40 kt jet just off the deck. Gusty winds will be more likely within areas of heavier rainfall, especially Tuesday. Low temperatures tonight should be close to our normal high temperatures, with some increase in temperatures Tuesday from the strong low level warm advection. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Highlights... * Period of strong to damaging wind gusts possible Tue into Wed * Heavy rain will result in an urban/street flooding threat Tue-Wed along with low risk of isolated flash flood threat * Less humid & more seasonable weather finally return Thu/Fri Tue night and Wed... Synoptic Overview... Slow moving cold front becomes parallel to upper flow as mid level trough takes on negative tilt. This front will be associated with an impressive warm conveyor belt up the eastern seaboard containing subtropical moisture with PWATs near the 2.00 inch mark, or nearly 3 std deviations above normal. Also embedded within this warm conveyor belt is very strong wind anomalies with 925 mb wind speeds of 55-65 kts, +4 std deviations above climo! This low level jet builds a low level thermal anomaly with nearly moist adiabatic lapse rates above this warm anomaly. This very strong low level jet also advects surface dew pts into the mid and upper 60s across southern New England late Tue into early Wed, generating MUcapes of 300-500 j/kg, very impressive for late Oct. Wind risk... As mentioned above low level jet peaks at about 55-65 kt late Tue into early Wed. Heavier showers (via precip drag) and especially potential low top fine line (very strong frontal convergence coupled with marginal instability) across western MA/CT will increase the risk for stronger winds aloft mixing to the surface. Given leaves remain on most trees, this will exacerbate the risk for downed limbs or even some trees with localized power outages. Wind headlines will likely be needed as we draw closer to the event. Heavy rain... Subtropical moisture streams up the eastern seaboard with PWATs nearing 2 inches, +4 std deviations from climo for about 24-30 hrs! This duration coupled with strong frontal forcing and marginal instability should be sufficient for periods of heavy showers with isolated thunder possible. Much of the global guidance offering a widespread 1-2" rainfall amounts with localized 3-5" possible especially eastern NY into western MA/CT given greater risk of low top fine line. Thu... Global guidance including ensembles suggest dry slot moves across the area, thus a drying trend develops. However cold pool aloft combined with cyclonic low may result in isolated diurnal showers especially across the high terrain. Otherwise mainly dry weather is expected. Turning less humid but only seasonably cool. Fri through the weekend... Looks like a period of short wave ridging between departing trough and next trough upstream arriving here Sunday or early next week. Ensembles suggest post frontal airmass Fri will be close to seasonably normal and continuing into Sat along with mainly dry weather. Ensembles also advertising long wave eastern seaboard trough reloads with new jet energy around Sunday with subtropical connection given high amplitude trough. && .AVIATION /15Z MONDAY THROUGH FRIDAY/...
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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/.... Through this afternoon...Moderate confidence mainly in timing of any showers developing over western areas during the afternoon. Some lingering MVFR-IFR conditions across portions of the region but should become mainly VFR by around 18Z or so. However, MVFR CIGS may return across western MA/N central CT during the late afternoon. May see isolated showers move into western areas after 18Z-20Z. S winds increase to around 10 kt. Tonight...Moderate confidence. Conditions lower to MVFR-IFR across N central and western areas this evening in scattered showers and patchy fog. VFR conditions to start across S central and eastern areas, but CIGS lower to MVFR to local IFR after midnight as showers slowly move E. Patchy fog will lower VSBYS to MVFR to local IFR as well. S winds gusting to 20-25 kt along S coastal areas after midnight. Tuesday...High confidence in trends. Moderate confidence in timing. Mainly IFR with occasional MVFR in low CIGS rain/fog. Some occasional TS also possible with heavy RA at times. Winds gust 20-30 kt most of the region out of the S-SE with a few gusts 30-40 kt mainly SE MA/Cape/Islands. Cannot rule out stronger gusts everywhere in heavier rainfall/thunderstorms. Areas of LLWS likely, especially after 15Z. KBOS Terminal...Moderate confidence in TAF due to timing issues with CIG improvement later this morning. Possible IFR could linger longer than current forecast. KBDL Terminal...Moderate confidence in TAF. Mainly VFR. May see brief MVFR-IFR VSBYS in patchy fog through 14Z or so but should improve by morning push. Outlook /Tuesday Night through Friday/... Tuesday Night: Mainly MVFR, with local IFR possible. Windy with gusts to 35 kt. SHRA, chance TSRA, patchy BR. Wednesday: Mainly VFR, with local IFR possible. Windy with gusts to 30 kt. SHRA, chance TSRA, patchy BR. Wednesday Night: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA. Thursday: Mainly VFR, with areas MVFR possible. Chance SHRA. Thursday Night through Friday:VFR.
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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. Short Term /through Tuesday/... Relatively light winds and seas continue across the waters into this evening. Increasing south winds ahead of a cold front will also mean building seas tonight into Tuesday, especially across the southern coastal waters. Moderate risk for gale force gusts Tuesday across most of the waters. Lingering pockets of poor visibility linger off E coastal Mass, but should improve during the early to mid afternoon. Outlook /Tuesday Night through Friday/... Tuesday Night: Low risk for gale force winds with gusts up to 35 kt. Rough seas up to 12 ft. Rain showers, chance of thunderstorms, patchy fog. Local visibility 1 to 3 nm. Wednesday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 13 ft. Rain showers, chance of thunderstorms, patchy fog. Local visibility 1 nm or less. Wednesday Night: Winds less than 25 kt. Rough seas up to 11 ft. Rain showers. Thursday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers. Thursday Night: Winds less than 25 kt. Local rough seas. Slight chance of rain showers. Friday: Winds less than 25 kt. Areas of seas approaching 5 ft.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Gale Watch from Tuesday morning through Wednesday morning for ANZ231>235-237-255-256. Small Craft Advisory from 8 AM to 6 PM EDT Tuesday for ANZ230- 251. Gale Watch from Tuesday afternoon through Tuesday evening for ANZ236. Gale Watch from Tuesday afternoon through Wednesday morning for ANZ250-254.
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&& $$ SYNOPSIS...Belk/Nocera NEAR TERM...Nocera/EVT SHORT TERM...Belk LONG TERM...Nocera AVIATION...Belk/Nocera/EVT MARINE...Belk/Nocera/EVT

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