Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 152029 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 429 PM EDT Sat Jul 15 2017 .SYNOPSIS...
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High pressure will bring a period of quiet, summer-like weather through tomorrow. Warm and humid conditions will continue through mid week with the threat for scattered afternoon and evening showers and thunderstorms Monday through Wednesday. A cold front may approach late Wednesday, then may stall across our region Thursday with the continued threat for scattered showers and thunderstorms.
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&& .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... Core of E-W moving vort max and associated upper lvl jet streak are moving across central MA/CT and heading E this afternoon. This combined with a very narrow corridor of overlapping K-indices near 30 (low-mid lvl column moisture) and lack of mid lvl subsidence continue to generate widely sct and very small core SHRA. Not seeing enough updraft strength, even in the heavier SHRA to yield lightning, as the cores are remaining near or below the freezing lvl. As such, will pull TS wording from wx for the remainder of the afternoon/evening as continued influence of subsidence and associated drying should further limit updrafts. Still, a few areas of E MA/RI may see a spot shower before the day is fully done. Slight chance POPs moving E through the evening reflect this thinking. Otherwise, the subsidence inversion provided by mid lvl ridging will lead to a gradual drying of the low-mid lvl column through the overnight, allowing these diurnally driven clouds to dissipate and the SHRA risk to gradually end. Therefore, will trend toward a dry overnight. Mins remain relatively mild as the subsidence will trap some of the moisture near the sfc and not allow it to mix out late this afternoon/evening. This will keep dwpts in the low-mid 60s, which is also where we expect mins to fall this evening. Some clouds possibly linger Cape/Islands, but these too should be dissipating as winds shift to the W. Localized ground fog possible, due to these higher dwpts and clearing skies. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... Tomorrow... Weak ridging continues to impact the region. H85 temps near +15C to +16C suggest plenty of room for mixing to the mid to even upper 80s in a few spots given a fair amount of sunshine outside diurnal clouds. Dwpts remain in the low-mid 60s, so still a bit on the sticky side. While this does suggest a slight increase in afternoon instability, the lack of overall forcing and dry air aloft should cap off any risk for showers. Dry POPs forecast. Tomorrow night... Weak return flow increases, drawing marine air across the region. Weak shortwave and mid/upper lvl moisture will provide some clouds across the region, although a few breaks are possible. Limited risk for development of marine stratus, but dwpts are near or below SSTs such that it may not develop with earnest. Still something to watch as S coastal areas could see late night fog/stratus which would linger into the early Mon AM hours. Upstream convection, although approaching from the W should dissipate within the dry air aloft, will be introducing some late night very low POPs across the W. Otherwise, another night with temps in the low-mid 60s as there is little change in airmass from the previous night. && .LONG TERM /MONDAY 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... Monday through Tuesday... Monday should remain dry for much of the region, with high pressure still lingering over the North Atlantic. Greatest instability expected to stay to our west. Expecting only a slight risk for a few weakening showers or thunderstorms to move into far western MA and northern CT, especially during the afternoon and evening. 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 /20Z SATURDAY 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/... Through the night tonight...Moderate confidence. Trend toward VFR everywhere this afternoon, however some lower CIGS (MVFR mostly) could hold at ACK/MVY/FMH/HYA through about 20-20Z then gradually dissipate this evening as winds shift to the W. Sea breezes continue along coastal terminals. Late night fog possible especially inland at typically prone airports. Tomorrow...High confidence. Any early AM fog burns off through 14Z. After this, VFR all sites. Sea breezes expected to begin 15-16Z. Tomorrow night...Moderate confidence. Mainly VFR to start, but a low risk for some S coastal low CIGS to impact mainly Cape/Island terminals with a lower risk at PVD/EWB. This could dip to low MVFR/IFR if the form, but they could stay offshore entirely. Winds shifting around to predominantly S. KBOS Terminal...High confidence in TAF. Low risk for early AM ground fog. Sea breezes 14-15Z Sun. KBDL Terminal...High confidence in TAF. Outlook /Monday through Thursday/... Monday into 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 Sunday Night/...High confidence. Winds shift out of the W briefly tonight, but then turn back to the S tomorrow. Winds should remain at or below 15 kt through the period, allowing seas to remain at or below 3 ft. Therefore, no headlines are expected through Sun night. Outlook /Monday 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...Belk/Doody NEAR TERM...Doody SHORT TERM...Doody LONG TERM...Belk AVIATION...Belk/Doody MARINE...Belk/Doody

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