Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 160659 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 259 AM EDT Sun Jul 16 2017 .SYNOPSIS...
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High pressure will bring fair weather along with warmth and humidity today. The warm and humid weather will continue through mid week along with with the threat for scattered afternoon and evening showers and thunderstorms Monday through Wednesday. One cold front approaches Tuesday, then dissipates. A second cold front may approach late Wednesday, then stall across our region Thursday with the continued threat for scattered showers and thunderstorms.
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&& .NEAR TERM /THROUGH TODAY/...
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High pressure in place over the region today. Mixing should reach to at least 850 mb, possibly to 800 mb. Cross sections show moisture near the top of this mixing, so the daytime heating will lead to a few cumulus clouds. The heating may also generate CAPE of 300-500 J/Kg. But subsidence should keep the instability from being fully realized, so no showers expected. Temperatures at 850 mb will be 15-16C, and at 800 mb will be 11-13C. Heating to these levels would support max sfc temps in the mid 80s, possibly near 90 in spots where the deepest mixing takes place. Wind fields will be light, and the daytime heating should generate sea breezes along the coast late this morning and afternoon.
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&& .SHORT TERM /TONIGHT THROUGH 6 PM MONDAY/...
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Tonight... Dry weather continues tonight. Dew points will be 60-65, similar to water temperatures off eastern Mass but several degrees cooler than water temps south of RI and Mass. Widespread fog moving ashore does not seem likely, but radiation fog inland is possible. With dew points 60-65, expect min temps in the low to mid 60s. Monday... High pressure builds offshore and brings a light south flow across our area. This may bring a slight increase in dew points during the day. Sunshine will bring mixing to at least 850 mb again, tapping temperatures of 14-15C and supporting max temps again in the mid 80s. Shortwave digging over the Great Lakes will turn the current westerly upper flow to come out of the southwest. A cold front being driven by that shortwave will slow to a stall Monday as it aligns with that changing upper flow. A broad zone of 1000-2000 J/Kg CAPEs will extend from Northern New England across New York State. CAPE values diminish rapidly across Western and Central Mass. Precipitable water values will be around 1.5 inches, not excessive but high enough to monitor. Expect thunderstorms to develop in the zone of instability to our west and north. It is possible that some of these storms could move east into our area during the late afternoon/evening.
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&& .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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Highlights... * Threat for scattered showers and thunderstorms at times Monday through Wednesday * Better chance for showers/thunderstorms late Thursday through Friday along a slow-moving front Overview... Mid level flow pattern is expected to change quite a bit next week. A mid level trough should amplify over New England to start out next week, then become more zonal during the middle of next week. This is expected to occur just slightly farther north than what we just had a few days ago, courtesy of a dominant subtropical ridge across the southern USA. Starting to see signs of another mid level trough across New England late next week. Still prefer a consensus approach to smooth over the less predictable, smaller scale features. Details... Tuesday... A weak low pressure may move through the Mid Atlantic and force a warm front close to the south coast of New England Monday night into Tuesday. Kept a slight chance for showers Monday evening, increasing to chance PoPs as the night progresses. The placement of this front will be tricky, owing to the nearly zonal flow in the mid levels. Only have moderate confidence in the placement and timing of this feature. As previously mentioned, the slight northward shift of the mean zonal flow pattern will mean increased temperatures and humidity. Currently thinking dew points should be high enough to make it uncomfortable for most. Locally heavy rainfall will also be a possibility, where it rains at all. Temperatures should be near normal. Wednesday and Thursday... We might be contenting with a pair of surface boundaries Wednesday into Thursday. It`s looking more likely a prefrontal trough should arrive Wednesday, followed by a slow-moving cold front for Thursday. Despite being rather weak, expecting above normal temperatures and high humidity to be in place. These boundaries don;t have to be strong to provide a focus for scattered showers and thunderstorms. Timing of these boundaries will be important to the forecast, and is an aspect in which there is only moderate confidence this far out in the forecast. Friday and Saturday... Low confidence continues for this portion of the forecast. It will all depend upon the southwards progress of a slow-moving cold front. Right now, Saturday looking much drier than Friday. Can see a scenario where more of Friday could be dry, too. Kept a chance for showers for Friday at this time.
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&& .AVIATION /06Z 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 Monday/... Today... Morning fog burns off quickly. Patchy IFR cigs/vsbys should give way to clear skies by mid morning. Aside from the fog, expect VFR conditions through the day. Light winds and daytime heating will allow sea breezes to develop along the coasts starting late morning. Tonight... VFR, but with areas of fog developing especially in the CT Valley. Local IFR cigs/vsbys in fog. Monday... Morning fog again burns off. VFR with developing light south wind. Sea breezes possible along the eastern Mass coastline. Thunderstorms will develop over NY State and Northern New England. It is possible a few of these will move into Western and Central Mass during the afternoon after 18Z, some with strong wind gusts. KBOS Terminal...High confidence in TAF. Seabreezes 14-15Z today, initially NE then turning SE. KBDL Terminal...High confidence in TAF. Outlook /Monday Night through Thursday/... Tuesday...Moderate confidence. SCT-BKN low-end VFR CIGS across the interior with SCT SHRA/TSRA. Best shot from central-W Mass into N central CT. Will see persistent S-SE wind flow, so MVFR- IFR CIGS move into coastal areas Mon night into early Tue. Will also see areas of MVFR-IFR VSBYS develop as well. Wednesday and Thursday...Moderate confidence, mainly for timing issues. Mainly VFR. Should see SCT-BKN low-end VFR CIGs with a better shot for scattered afternoon/evening SHRA/TSRA activity. MVFR-IFR lingering across the S/SE coast in areas of fog, mainly late night/early morning.
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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 Monday/...High confidence. Winds less than 15 knots and seas less than 5 feet through the period. Sea breezes developing along the coastline. Outlook /Monday Night through Thursday/...Moderate confidence. Rather tranquil boating conditions during this portion of the forecast. One concern for mariners will be scattered showers or thunderstorms at time Monday into Wednesday. Not going to be a washout by any means, although locally heavy rainfall will be possible. Another concern will be the possibility of areas of fog reducing visibility, especially each night.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/Belk NEAR TERM...WTB SHORT TERM...WTB LONG TERM...Belk AVIATION...WTB/Belk MARINE...WTB/Belk

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