Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 191925 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 325 PM EDT Tue Jun 19 2018 .SYNOPSIS... Dry weather is expected tonight and Wednesday as high pressure builds over New England. Showers are likely Wednesday night, especially south of the Mass Pike, as low pressure passes offshore. High pressure from Canada brings dry weather Thursday and Friday. A cold front them brings a chance of showers over the weekend, followed by dry weather early next week. && .NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/... Any lingering diurnal clouds will dissipate toward sunset, giving way to clear skies and diminishing winds tonight. This will allow for good radiational cooling away from coast. Sided closer to cooler MOS guidance which gives lows in upper 40s to mid 50s. Airmass remains dry enough to preclude mention of patchy fog. && .SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/... High pressure over SNE heads offshore in afternoon, resulting in S/SW flow across region. Airmass remains dry as seen in model cross sections so just expect some diurnal clouds to form, but overall plenty of sunshine. Highs should run a few degrees cooler than today, ranging from mid 70s on South Coast, Cape, and Islands to the mid 80s inland. Models in good agreement on arrival of showers Wednesday night as short wave passes and weak surface low pass south of New England. Main issue is how far north do the showers extend into SNE. Right now we are most confident for CT, RI, and SE MA which come under influence of best theta-e advection and lower level convergence/ moisture transport. Blended in high-res ARW WRF which gives as much as 0.50 to 0.75" of rain. Farther north, it will be a battle with dry air pushing down from northern New England, so it`s possible areas along and north of Mass Pike remain dry. && .LONG TERM /THURSDAY THROUGH TUESDAY/... Highlights... * Lingering showers, south coast on Thursday * Dry and seasonable on Friday * Unsettled weather for the weekend Overview... 12z models show good agreement with the flow pattern evolution during the long term increasing forecaster confidence. Northern stream flow will feature a persistent upper ridge over central Canada with a couple of frontal waves moving across the central U.S. New England will remain on the edge of an upper level trough over the Maritimes keeping the region in northwest flow. Passing wave from the Midwest will impact southern New England over the weekend before northwest flow returns for next week. As an FYI, the Canadian model indicates the formation of a nor`easter early next week but this is not supported by its own ensemble mean nor the GFS and ECMWF solutions. Details... A few lingering showers on Thursday morning thanks to passing wave to the south. Conditions will improve in the afternoon with seasonable temperatures. High pressure on Friday will lead to dry weather and temperatures near normal. Sea breeze potential possible. Unsettled weather returns for the weekend as a low pressure from the Great Lakes passing through northern New England. Associated warm and cold front will sweep through resulting in a warm frontal showers on Saturday followed by showers and thunderstorms on Sunday with approaching cold front from the west. Still some timing issues but appears precip will impact this upcoming weekend, luckily not a washout. Canadian high pressure will move in behind the front on Monday lasting into the work week resulting in dry weather. && .AVIATION /20Z 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. VFR. N/NW winds gust to 20-25 kt through late afternoon before diminishing and becoming light/variable tonight. SW winds prevail Wednesday and Wednesday night. Showers likely across CT, RI, and SE MA Wednesday night with areas of MVFR or perhaps IFR ceilings. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Thursday through Sunday/...Moderate confidence. Thursday through Friday Night: VFR. Saturday: Mainly VFR, with local MVFR possible. Chance SHRA. Saturday Night: Mainly VFR, with areas IFR possible. Chance SHRA, isolated TSRA. Sunday: Mainly VFR, with local MVFR possible. Chance SHRA, isolated TSRA. && .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. Diminishing N/NE winds and seas tonight as high pressure builds over SNE. SW flow develops Wednesday and Wednesday night as the high becomes centered offshore. Winds and seas remain below 25 kt and 5 ft respectively, but recreational boaters should be aware of 15-20 kt gusts and locally choppy seas of 2 or 3 ft on Narragansett Bay and south coastal sounds Wednesday afternoon. Reduced visibility in showers and patchy fog Wednesday night, especially on south coastal waters. Outlook /Thursday through Sunday/...Moderate confidence. Thursday: Winds less than 25 kt. Slight chance of rain showers, patchy fog. Thursday Night through Friday Night: Winds less than 25 kt. Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers. Saturday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers, isolated thunderstorms. Sunday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers, isolated thunderstorms. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Dunten/JWD NEAR TERM...JWD SHORT TERM...JWD LONG TERM...Dunten AVIATION...Dunten/JWD MARINE...Belk/Dunten/JWD is the U.S. government's official web portal to all federal, state and local government web resources and services.