Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 260700 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 300 AM EDT Wed Jul 26 2017 .SYNOPSIS...
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High pressure will bring dry and warmer weather today but the risk of showers and t-storms returns Thursday. A coastal storm will emerge off the Mid Atlc coast Friday and is expected to track south of New England Friday night into Saturday possibly bringing a chilly rain to portions of the region. Dry and seasonable conditions return late next weekend into early next week.
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&& .NEAR TERM /THROUGH TODAY/...
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High pres in control today with dry airmass yielding lots of sunshine with some afternoon cu developing. More seasonable temps today in the upper 70s to around 80 which will feel nice after the recent unseasonable cool weather, but these temps are still below normal for late July. Somewhat cooler temps along the immediate coast where seabreezes will develop.
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&& .SHORT TERM /TONIGHT THROUGH 6 PM THURSDAY/...
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Tonight... Approaching mid level shortwave from the NW will result in increasing mid/high clouds. Mainly dry conditions expected as main focus for late night showers will be to the north. Lows will range from the upper 50s to lower 60s. Thursday... Another mid level shortwave approaches from the north with increasing deep layer moisture and instability as K indices increase into the 30s and CAPES 500-1000 J/kg. This will bring the potential for sct showers and t-storms, especially interior where instability is greatest. 0-6km shear 30-35 kt so can`t rule out a few strong storms but instability will likely be a limiting factor. Some sunshine is expected, especially near the coast but generally looking at more clouds than sun with highs mid/upper 70s. Becoming a bit more humid as dewpoints climb into the mid 60s.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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Highlights... * Best chance for showers/scattered thunderstorms Thursday night through Friday night * A few showers linger into Sat, then dry but cool conditions * Dry and seasonable weather likely Sunday into Monday Overview and model preferences... Weak H5 ridge pushes E to the Maritimes early in this period, while digging H5 trough moves E-SE out of the Great Lakes. However, individual model solutions vary on the intensity of the trough as it shifts E. This is giving widening surface solution spread as the surface front and possible wave development during the Thu night-Fri timeframe. 12Z GFS appears to be an outlier as it pushes this system further S late this week and keeps the wave weaker/further S. Also, GFS blasts the H5 short wave offshore by late Thu/Thu night, while most of the remaining suite is slower. A few members even try to develop H5 bubble cutoff in the NW flow over the western Great Lakes Thu night/Fri and move it eastward. While the GFS moves the surface front offshore, the 12Z GGEM and 00Z ECMWF keep the front a bit further N but also have low pres moving along it. The 12Z NAM is a bit more toward the GGEM/EC camp, though a bit further S with the developing low over the lower Appalachians. By Friday night, most models have the low passing S of New England, but northern fringe of the precip may reach into the region though each solution varies on how far N the precip shield extends. Have low to moderate confidence during the late week timeframe. Am leaning toward a non-GFS blend especially for the Thu night to Fri night timeframe. Beyond this, should see the H5 trough move offshore during the upcoming weekend, but noting broad long wave troughing setting up across the eastern half of the U.S. while high amplitude ridge builds from the west coast into British Columbia. Should see generally dry but cooler than seasonal norm temps with continued NE wind flow as surface high builds across the western Great Lakes/northern Plains. Overall, will use blend of models/ensembles for this timeframe. Details... Thursday night through Friday night... Models continue to signal low pressure wave shifting E from the Ohio valley along the passing cold front. Some model differences in frontal placement and how quickly the low moves E. At this point, looks like best chance for showers/scattered thunderstorms will occur during this timeframe. Decent instability with this front. Best shot for precip will occur mainly near and S of the Mass Pike where likely POPs are in place. Noting good slug of QPF pushing through, with 1-1.5 inches possible across S coastal RI and SE Mass during this timeframe. Winds shift to N-NE as the low passes during Fri, then will pick up late Fri/Fri night mainly along the S coast as H925 jet up to 40-45 kt passes. Winds may gust up to 20-25 kt along the immediate S coast/Cape Cod and the islands for a time mainly around or after midnight Fri night. Saturday... Showers may linger along the S coast through at least midday Sat, depending upon how fast the low pushes offshore, allowing the front to move further S. Conditions should improve during the afternoon but it will be cool with NE winds in place for most of the day. Highs will only be in the 70s. Sunday-Monday... Looks dry as high pressure to the W holds in place. Light winds will be in place as well. Temps will rebound close to seasonal levels. Tuesday... Low pressure may develop on the front S of New England, while another cold front approaches from the NW with its own wave. Big question will be how quickly the northern front approaches. Kept only slight chance POPs for the entire area for now. Temps continue close to seasonal norms. Rather low confidence.
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&& .AVIATION /06Z WEDNESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/... Through 12z...Mainly VFR. Patchy fog in portions of the CT valley and interior E MA. Today and Tonight...High confidence. VFR. Coastal sea breezes developing by midday. Thursday...Moderate confidence. Mainly VFR cigs with patchy MVFR. Scattered showers and t-storms developing, especially interior with brief lower conditions. KBOS Terminal...High confidence. Sea breeze expected by 15z. KBDL Terminal...High confidence. Outlook /Thursday Night through Sunday/... Thursday night through Friday night...Moderate confidence. Mainly VFR CIGS, but pockets of MVFR-IFR in heavier SHRA/isolated TSRA. Areas of widespread SHRA mainly from the Mass Pike S late Thu night and Fri, with sct SHRA N of the Pike. Patchy late night/early morning fog with local IFR VSBYS. Winds will be shifting through the period, but cannot rule out some gusts to around 20 kt as these shifts occur. Saturday...Moderate confidence. May see pockets of MVFR conditions along S coast in lingering SHRA and patchy fog. Otherwise mainly VFR. NE winds gusting to around 20 kt from Plymouth county southward through midday then diminish. Sunday...Moderate to high confidence. VFR. Light N-NE winds with local sea breezes. && .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 Thursday/...High confidence. Today...High pres over the waters will result in quiet boating weather with light winds and seas and nearshore seabreezes developing. Tonight...Winds turn southerly as high moves offshore. Light wind speeds, but may approach 20 kt over NE MA waters. Thursday...S/SW flow with gusts to 20 kt. Seas below SCA thresholds. Outlook /Thursday Night through Sunday/... Conditions should be mainly below small craft criteria for most of this period. May see N-NE winds gusting up to 25 kt on the southern open waters late Fri night through Sat as front passes. Seas also build up to 5-6 ft on the southern outer waters for a time Sat into Sat evening. Rain and fog will lead to visibility restrictions especially Thu night into Fri.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...KJC NEAR TERM...KJC SHORT TERM...KJC LONG TERM...EVT AVIATION...KJC/EVT MARINE...KJC/EVT

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