Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 270711 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 311 AM EDT WED JUL 27 2016 .SYNOPSIS... High pressure will bring dry but continued hot conditions through Thursday. A cold front will drop southward across southern New England late Thursday and stall near the south coast Friday. Low pressure will move from the Mid-Atlantic northeastward toward southeast MA by Fri night, then exiting the coast Saturday. This has the potential to bring some rain to much of the area. A few showers are possible over the weekend. Then dry high pressure builds over the northeast states early next week. && .NEAR TERM /THROUGH TODAY/... High pressure builds overhead bringing sunny skies and light shifting wind. The solar heating will allow temperatures to climb quickly during the day, and the light wind will allow sea breezes to develop along the coasts around midday. The heating will build the mixed layer to at least 800 mb and possibly a little higher. Forecast temperatures at that height would be equivalent to 18-19C at 850 mb. So expect max surface temps in the low to mid 90s, buffered a little at the shoreline by the sea breeze. No change to humidity levels. Heat index values in the low 90s. && .SHORT TERM /TONIGHT THROUGH 6 PM THURSDAY/... Tonight... High pressure moves offshore but maintains fair skies and light wind. Light south winds possible by morning, but advection of higher dew points limited. Expect similar min temps, mainly in the upper 50s and 60s. The light flow may also allow some patchy fog in the valleys. Thursday... High pressure offshore with south to southwest winds over New England. Fair skies will again allow deep mixing. RH fields below 850 mb remain dry while some moisture increase at 800 mb would allow increasing clouds during the afternoon. Temperatures in the mixed layer are equiv to 19C at 850 mb, so low to mid 90s again looks reasonable. Depending on the strength of surface winds, there may be another buffering sea breeze along the eastern MA shore for part of the afternoon. But confidence in a persistant sea breeze is low at this time. This leaves the question of precip. Moisture and instability is initially focussed on Northern New England but could slip south into Northern/Western MA late afternoon/evening. Models do show a surface front moving south into our area, but also show moisture and favorable jet dynamics remaining in Northern New England. Plenty of dry air below 850 mb to interfere with showers. We will show chance pops moving into Northern/Western MA starting 21Z, with slight chance into Northern CT. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Will a storm system come close enough to give substantial rain to parts of the area Friday and Friday night? Overview and model preferences... At upper levels, zonal flow Thursday becomes west-southwest as a Great Lakes short-wave trough approaches and then crosses the area Friday night and early Saturday. Another short-wave trough over the Great Lakes Saturday exits New England late Sunday and Monday. Drier and increasingly warm upper northwest flow then develops over New England early next week as a strong high pressure ridge develops over the Midwest. At the surface, a weak frontal boundary will move southward into southern New England late Thursday into Friday and stall along the south coast. 12Z models are in much better agreement that a low pressure storm system will develop in the Ohio Valley...move to the Mid-Atlantic, then head northeast toward our area. GFS is now the farthest south solution. GEFS low track is farther north, though, closer to the GGEM, ECMWF, and NAM. While it is way too early to gets hopes up about substantial rain, this is our best chance in a while. Good model agreement on high pressure building in from the north by Monday and Tuesday of next week. Details... Thursday night...Increasingly muggy. Can`t rule out a chance of a shower or isolated thunderstorm. Lows in the upper 60s to near 70. Friday and Friday night... All models are coming into more agreement...giving us more confidence...that a low pressure storm system will move from the Mid-Atlantic northeastward toward southeastern MA. All models give some rain to our region. Some are much more prolific than others. Of course, we are in a drought and even missed out on yesterday`s convection, so it will be important to see consecutive model runs over the next couple of days. For this model cycle, the NAM has an intense low moving into SE MA Friday. afternoon and evening, with heavy rains in parts of RI and SE MA. The ECMWF is very similar with track and heavy rains even a little farther north, but not until Friday night. The GGEM is also on board with a low, albeit weaker, passing southeast of Nantucket with light amounts. The GFS is farthest south, with just a few hundredths of rain. However, the GEFS ensembles are farther north than the operational GFS, more in line with the other models. That said, have forecast cloudy skies with showers and isolated thunderstorms likely...both Friday and Friday night, except high chance PoPs in northwesternmost areas. Highs only in the lower to mid 80s. Saturday and Sunday... Low pressure departs the coast Saturday morning. A weak pressure pattern exists, with some lingering moisture around. So, basic summer weather with partly cloudy skies, highs in the 80s, and a low chance of a scattered mainly afternoon and evening shower or thunderstorm. Monday and Tuesday...Expecting high pressure to build over northern New England, providing increasing sunshine. Just a slight chance of a shower in northwest areas Monday and dry on Tuesday. Highs Monday 80 to 85 with mid and upper 80s possible on Tuesday. && .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/...High confidence. Today... VFR. Light wind will allow sea breezes to develop along the coastline starting late morning. Tonight... VFR. Light variable wind. Patchy fog possible with MVFR/IFR cigs/vsbys overnight. Thursday... VFR. Local MVFR cigs/vsbys in northern/western MA during the late afternoon due to scattered showers/tstms. KBOS TAF... VFR. High confidence. Light variable wind will allow a sea breeze to develop around 15Z. KBDL TAF... VFR. High confidence. Light variable wind. Outlook /Thursday Night through Sunday/... Thursday night...Moderate confidence. VFR except areas of IFR in patchy fog late at night especially south coast. Also, MVFR possible in any scattered showers/thunderstorms. Friday into early Saturday morning...Moderate confidence.. VFR early Friday lowering to MVFR throughout the region by afternoon. IFR possible in showers and thunderstorms. Locally heavy downpours possible. Areas of fog. Rest of Saturday and Sunday...Moderate Confidence. Mainly VFR, except MVFR CIGS/VSBYS possible in scattered showers and thunderstorms. Potential for local MVFR-IFR in patchy fog and low CIGS Sat night. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/...High confidence. Winds remain below 25 knots and seas below 5 feet through the period. Sea breezes will develop near shore late this morning and afternoon. Winds become south to southwest Thursday. Outlook /Thursday Night through Sunday/...Moderate to High confidence. Thursday night...Winds and seas below small craft criteria. Patchy late night/early morning fog with reduced visibilities. Isolated showers/thunderstorms possible Thursday night. Friday-early Saturday...Southeast winds become northeast. Speeds generally 10-20 kt, depending on strength of possible low pressure approaching from the mid-Atlantic. Swells will build to 4 to 5 ft on the southern outer waters by Friday night into early Saturday. Patchy fog. Reduced visibilities in showers and thunderstorms. Rest of Saturday and Sunday...Seas subsiding with northeast winds becoming southeast...generally 10-15 kt or less. && .FIRE WEATHER... Dry conditions are expected to persist Today and Thursday across Southern New England. Minimum relative humidity values will be 30 to 40 percent inland both days, and 40 to 60 percent along the South Coast. Less wind Today than Tuesday, becoming a sea breeze along the coast late this morning and afternoon. Wind directions become more southerly on Thursday but remain below 15 knots. Concern for Thursday will be how far south showers/tstms reach. Most support is in Northern New England, but scattered showers/t-storms could reach Northern/Western MA late afternoon. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/GAF NEAR TERM...WTB SHORT TERM...WTB LONG TERM...GAF AVIATION...WTB/GAF MARINE...WTB/GAF FIRE WEATHER...

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