Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 261904 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 304 PM EDT Mon Jun 26 2017 .SYNOPSIS...
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Additional upper level disturbances move across New England early tonight and later Tuesday, bringing a few showers and isolated thunderstorms. The greater threat will be on Tuesday. A warming trend begins for the latter half of the week with a return to summer heat and humidity Friday and Saturday. A warm front may bring some showers Thursday night with more showers and thunderstorms possible Friday through the weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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Scattered showers and isolated thunder will be possible through the evening as a weak shortwave passes to our north. Stability parameters are marginal for thunder, but enough to include a mention. Best chance will be in areas north of the Mass Pike. Convection diminishes early tonight. Expect quiet weather overnight. Of note, the GFS develops an area of showers around midnight between Washington and Philadelphia, then moves it up through NYC into Southern New England by 12Z. The ECMWF and NAM show nothing, as does the SPC HRRR. The GGEM shows nothing to our south but develops a few hundredths over Southern CT by 12Z. Inclination is to treat the GFS pcpn as an outlier. Dew points in the 50s again tonight, so expect similar min temps... 50s and lower 60s.
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&& .SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
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Sharp shortwave over the Great Lakes today moves through the cyclonic flow. One part ejects across NY and Northern New England Tuesday afternoon/evening, while the main portion crosses our area late Tuesday night or Wednesday morning. We remain on the edge of the cold pool Tuesday, but close enough to expect mid level lapse rates of 6.5 to 7C/Km during the afternoon and early night. Going along with this will be Totals in the lower 50s and LI values below zero, as well as SBCAPE values of 500-1000 J/Kg. Theta-E values show a ridge over CT during the afternoon/evening. Expect scattered showers/tstms during the afternoon and early night. Winds aloft show some support for a few strong or damaging storms. Winds at 850 mb will be 20-30 knots during Tuesday afternoon, although this is forecast to move offshore by evening. Winds at 500 mb are forecast at 50-60 knots during Tuesday afternoon, but also move offshore by evening. Timing of this wind and of the shower/tstm development may be the determining factor in how strong these storms may get. The mixed layer is expected to reach near 850 mb, where winds as noted above will be 20 to 30 knots. Our forecast includes gusts on the lower half of that range, but slightly higher values are possible. With the main shortwave moving through during Tuesday night, and with the upper cold pool moving overhead, expect a continued chance of showers/storms Tuesday night. If mixing reaches 850 mb it will work on temps of 8-10C, which suggests max sfc temps of 75 to 80. If mixing goes a little higher, such as to 800 mb, then max sfc temps would be more centered around 80. No change in the airmass Tuesday night compared with tonight, so expect similar min temps.
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&& .LONG TERM /WEDNESDAY THROUGH MONDAY/...
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Highlights... * Pleasant Wednesday with low risk of a shower * Heat and Humidity return Friday into Sunday * Thunderstorm chances increase Thursday night through Sunday Pattern Details... 00z guidance is in general agreement synoptically with some difference in strength and timing for each wave late in the week. Upper level trough will move through the flow Tuesday night with southern New England on the backside Wednesday. Quasi-zonal flow will set-up across the region on Thursday with the flow with becoming more amplified by the weekend. Resulting in a broad trough over the Great Lakes and another trough over the mountain West with weak ridge between the two. Because the flow is becoming more amplified, sub-tropical ridge is also building closer to the region late in the weekend. Ridging out West by Sunday will push the Great Lakes trough towards the Northeast for early next week. Details... Wednesday... Trough axis will be offshore by Wednesday putting southern New England in weak northwest flow. Depending on how quickly precip moves offshore, Tuesday night may be quite pleasant with temperatures in the low to mid 50s with low humidity. Mid level shortwave and assocd mid level cooling which brought the showers and t-storms to SNE last night has lifted to the NE. Weak subsidence behind this wave will maintain dry conditions through the morning. Another weak shortwave approaches from the SW this afternoon and will bring a few showers and isold t-storms, mainly interior. SBCAPES are marginal, 200-400 J/kg, and 500 mb temps are actually warming slightly today which should result in limited coverage of convection. Mainly dry in RI and SE MA as rather dry air in the mid levels along with very low KI values near the coast will likely keep any showers and t-storms to the north and west so we have dry conditions here. 850 mb temps around 10-11C will result in max temps in the upper 70s to lower 80s. Comfortable humidity levels with dewpoints down in the upper 40s and lower 50s. Surface high pressure will slide into the area on Wednesday as ridging builds a loft. Steep lapse rates with some moisture in the mid-levels will help develop diurnal CU by the afternoon. Mixing up to 750 mb will result in temperatures in the upper 70s with breezy westerly flow near 20-25 MPH. Guidance shows very little QPF on Wednesday, but cannot rule out a few pop-up showers by the late afternoon hours. While confidence is higher north of the region, southern New England will see instability values above 500 J/kg with K values above 25C. This may be enough for a spot shower. Winds aloft will begin to turn more to the southwest by Wednesday night with WAA. Overnight lows will remain around 60. Thursday... Dry day to start as high pressure will slide south of the region. The flow will turn more active with Zonal flow aloft and a few weak waves passing through. Impressive warming aloft as surface warm front pushes through the region. This will push southern New England in the warm sector resulting in increasingly warm and humid temperatures. Scattered showers and thunderstorms are anticipate by the latest guidance suggests not until the evening hours as mid-levels will remain quite dry. A weak shortwave moves through the flow Thursday evening/night. With zonal flow and both 850mb isotherms and winds becoming parallel, appears that anything the fires across upstate NY will ride through the flow moving into the area. In fact, guidance is indicating a lingering MCS will move through the flow overnight which could result in a few strong storms, esp north of the Pike. This region has the best area of instability and 0-6 km shear values. Still uncertainty on where this will set-up as it could still move north of the region, or south. Something to watch over the upcoming week. Friday into Sunday... Unsettled weather patter for this time period as southern New England remains in the warm sector with heat and humidity. With 850 mb temps near 2 STD above normal, appears that the potential for 90 degrees returns on Friday and Saturday. Back door cold front appears to remain well north of the region per latest GFS and EC. Thus have gone above guidance for Saturday temps. Heat headlines may be needed. Chance for showers and thunderstorms each day, but difficult to place the exact timing and location of any strong storms. Regardless, the potential for strong to severe weather appears possible through the period as frontal boundary lingers north of the region. One caveat to watch is the subtropical ridge. If this ridge moves closer, it may keep portions of the area dry.
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&& .AVIATION /18Z MONDAY THROUGH SATURDAY/...
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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 Night/...High confidence. This evening and tonight... VFR. Scattered to broken cumulus with bases 5000-6000 feet. Scattered showers and isold t-storms in the interior, mainly along/north of the Mass Pike. Showers and tstms should diminish during the early night. Tuesday... VFR. Scattered to broken cumulus with bases 5000-6000 feet. Scattered showers and thunderstorms expected from midday through the first part of Tuesday night. Showers and storms may bring briefly lower conditions, mainly vsbys 3-5 miles in heavier showers. Southwest winds will gust to at least 20 knots and possibly as high as 30 knots. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Wednesday through Saturday/... Wednesday...High confidence. Mainly VFR. NW gusts to 20 kts. Thursday...Moderate confidence. Mainly VFR. Afternoon showers possible in the interior with showers/t-storms possible all SNE Thu night. Gusty SW winds to 25-30 kt developing, especially coastal plain. Friday...Moderate confidence. Patchy early morning fog, with local MVFR. Then VFR, except local IFR in possible strong thunderstorms, mainly during the afternoon and evening hours.
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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 Night/...High confidence. Winds and seas mostly below Small Craft Advisory thresholds through the period with SW flow. A few gusts to 20 knots expected with potential for a few gusts to 25 knots especially nearshore. Outlook /Wednesday through Saturday/... Wednesday...High confidence. Quiet boating weather with winds and seas below SCA. Gusts to 20 kt possible nearshore waters. Thursday...Moderate confidence. Small craft advisories will likely be needed. Increasing SW winds with gusts to 25+ kt likely, especially over nearshore waters. Building seas may reach 6 to 8 ft over southern waters Thu night. Friday...Moderate confidence. SW winds continue, mainly 20-25 kt with building seas. Scattered thunderstorms, some with reduced visibilities and strong gusty winds.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/Dunten NEAR TERM...WTB/Dunten SHORT TERM...WTB LONG TERM...Dunten AVIATION...WTB/Dunten MARINE...WTB/Dunten

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