Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 272043 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 443 PM EDT Tue Jun 27 2017 .SYNOPSIS... Upper shortwave and associated jet stream will maintain showers and thunderstorms through this evening. A few of the storms may contain gusty winds and small hail. High pressure builds fair and dry weather for Wednesday. A warming trend begins for the latter half of the week. Expect summer heat and humidity from Friday through the weekend. A warm front passes Thursday night, bringing scattered showers and thunderstorms. More showers and thunderstorms are possible from Friday through the weekend. A cold front tries to shift toward the region early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Showers and thunderstorms have bubbled up and will linger through the evening. Strong low level winds and cold temps aloft are contributing to the strength of these storms. SPC has maintained a Marginal Risk for severe weather for areas west of I-95. Considering all of this, we will maintain some enhanced wording for strong winds and small hail in the forecast. Once the convection dies down, expect dry weather the remainder of the night. Light winds and mostly clear skies will allow fog to form in some spots, especially parts of the CT Valley. Dew points in the upper 40s and 50s should leave room for temps to cool down into the 50s most places by early morning. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... The upper trough is overhead along with its cold pool. So continued support for lift. But the airmass will be much drier with a moist layer limited to the 750-850 mb layer. Expect diurnal clouds but precip is unlikely. Temps aloft will be equivalent to 8-10C at 850 mb, supporting max temps 75-80. High pressure maintains mostly clear skies and light wind should allow overnight temps to reach the 50s, with lower 60s in the urban areas. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Highlights... * Scattered showers/thunderstorms from Thursday night through Sunday night * Very warm, humid conditions return Friday, lasting through the weekend Overview... 12Z medium range models and ensembles continue same theme for summer conditions. Active northern stream in place with a broad mid level fast flow that looks to continue through the upcoming weekend at least. H5 short wave/cutoff low moves out of Saskatchewan and Manitoba on Thursday, which will push across southern Canada into the northern Great Lakes through this weekend, then into Quebec Monday. Weak short waves will move along in the general W-SW steering flow around the base of the cutoff low through the broad trough to its S and SW. Will see rounds of scattered showers/thunderstorms as each short wave moves across. Very sultry airmass in place thanks to Bermuda high sitting off the Carolina coast. Will see dewpts rising to the mid-upper 60s late this week through the weekend. The offshore high and western Atlantic mid level ridging will cause an approaching cold front to stall west of the region. Question will be when the H5 trough will move across the region early next week. Model solution spread leading to lower confidence on timing of cold front that may approach around Monday or the 4th of July. Details... Thursday-Thursday night... High pressure off the mid Atlantic/SE U.S. coast will keep dry conditions across the region through about midday Thursday. A warm front will start to approach, with some showers that may develop across N and W Mass, mainly N of the Mass Pike around or after 21Z. Will see some more instability start to work into W Mass/N central CT Thu night as the warm front moves across, so have included chance thunder from W-E. Highs Thursday will mainly be in the lower-mid 80s away from the S coast, only in the 70s along the S coast. Overnight lows will be in the mid-upper 60s. Friday through Sunday... With the ridge in place off the coast, continued SW flow through this period. Typical summertime airmass in place, with dewpts up to the mid and upper 60s with a few spots that may touch 70, along with H85 temps rising to +16C to +18C Fri-Sat. With the soupy airmass, will likely see nighttime fog develop mainly around or after midnight as temps fall back close to the higher dewpts. Will see scattered showers and thunderstorms from the midday through evening hours each day, especially across the interior. Looks like best shot for convection will occur Friday afternoon/evening, then again Saturday especially over western areas. The ridge offshore may allow for somewhat drier air and subsidence to move into coastal areas on Saturday, so could be drier during the daylight hours. Approaching cold front on Sunday will trigger another round of convection as well. Will likely see some brief heavy downpours in some activity thanks to PWATs increasing to 1.5 to 1.8 inches, especially Friday afternoon/evening and again Sat night-Sunday. Some question as to whether some stronger storms will develop during this timeframe. Will continue to monitor this aspect. One other issue is possible heat headlines on Fri and Sat, due to combination of high temps (lower 90s) and dewpts (up to 70 degs). Could reach high indices close to 95, which would trigger possible advisories. Current forecast suggests lower 90s. Will monitor this as well. Monday-Tuesday... Low confidence on this portion of the forecast due to model solution spread, mainly with frontal passage. Some question on frontal passage late Sun night or Mon morning which will wash out rather quickly as winds shift back to SW during Mon afternoon. Another front may approach during Tue which may trigger more convection. && .AVIATION /21Z TUESDAY THROUGH SUNDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/...High confidence. This evening and tonight... Areas of MVFR cigs/vsby in showers/tstms. Hail and strong wind gusts possible. Showers diminish and skies clear after 02Z/10 PM. Areas of fog possible after midnight with the best chance in the CT River Valley north of Springfield. Wednesday... VFR and drier weather. Showers/tstms will fire again north of Mass, but all quiet in Southern New England. West-northwest winds. Wednesday night... VFR. Light winds and clearing skies. Patchy fog possible late at night. KBOS Terminal...High confidence in TAF. Showers and T-storms likely this evening. A few of the stronger storms may contain small hail and gusty winds. KBDL Terminal...High confidence in TAF. Showers and T-storms diminish this evening. Outlook /Thursday through Sunday/... Thursday...High confidence. Mainly VFR. Dry through midday, then scattered afternoon/ evening showers across N and W Mass mainly N of the Mass Pike. Showers/ thunderstorms possible entire region Thu night. Gusty SW winds to 20- 30 kt developing along the S coast late Thu/Thu night. Friday through Sunday...Moderate confidence. Patchy early morning fog each day with local MVFR-IFR conditions. Otherwise mainly VFR. Local MVFR-IFR in possible strong thunderstorms, mainly during the midday through evening hours. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday Night/...High confidence. Tonight... Showers and thunderstorms over land will move over parts of the waters this evening. Best chance will be along the Massachusetts North Shore. Southwest wind continues with gusts between 20 and 25 knots on the southern waters this evening before diminishing. Small Craft Advisory continues through the evening and then ends around 8 PM as winds diminish. Seas generally 3 feet or less. Wednesday and Wednesday night... Winds become WNW at modest speeds. Seas 3 feet or less. Outlook /Thursday through Sunday/... Thursday...Moderate confidence. Small craft advisories will likely be needed. SW winds will increase, with gusts to 25-30 kt highest across the southern outer waters. Seas build to 6 to 8 ft over southern waters Thu night. Friday...Moderate confidence. SW winds continue, gusting to around 25 kt, diminishing after midnight Fri night. Seas up to 5 to 7 ft. Scattered thunderstorms, some with reduced visibilities and strong gusty winds. Patchy late night fog. Saturday-Sunday...Moderate confidence. SW winds continue, though diminishing. Seas around 5 ft on the outer waters Sat, then slowly subside. Patchy late night fog each night with reduced visibilities. Chance of showers/thunderstorms. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230>237-251. && $$ SYNOPSIS...WTB/EVT NEAR TERM...WTB SHORT TERM...WTB LONG TERM...EVT AVIATION...WTB/EVT MARINE...WTB/EVT

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