Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 292300 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 700 PM EDT WED JUN 29 2016 .SYNOPSIS... Dry and seasonable weather arrives tonight into Thursday. A cold front moves over the region on Friday into early Saturday, a few thunderstorms are possible. High pressure builds in behind the front and prevails through early next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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700 PM Update... Overall trend in strong storms continue to diminish this evening. ML CAPE values are still above 1000 J/KG and with good low level moisture combined with colliding outflow boundaries, a rogue shower is still possible. However latest water vapor imagery shows bulk of dry air moving into the region. K indicies have also dropped off over the past hour. This will limit shower potential an thus an isolated chance is possible. Frontal system continues to slowly move across the region. Looking at latest obs, surface dewpoints paint the picture as there is a 10 degree dewpoint difference within a few miles of each other. Example, KBED dewpoint is at 54F with KOWD at 69F. Lower dewpoints will continue to move eastward overnight tonight. Skies are also beginning to clear out. This may lead to the development of radiational fog, especially where the higher dewpoint air is located. Appears the fog wont develop til near midnight as temps drop and temp/dewpoint spread will be low. Otherwise expect more comfortable conditions to move into the region tonight. Overnight lows will drop into the upper 50s to low 60s away for the urban regions.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Dry weather expected through this period, although our region will only be on the edge of a high pressure to our south. The main limitation will be the lack of moisture. Seasonable temperatures expected. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... HIGHLIGHTS... * Scattered showers and thunder Friday/Saturday from passing front * Cooler and less humid for Sunday into July 4th Holiday * Summer heat is possible by mid next-week OVERVIEW... The 12Z guidance is in good agreement for the medium range, however, it has begun to diverge beginning on Monday into next week. Upper low south of Hudson Bay will rotate through the mean trough and pass through eastern Canada by the close of the weekend. The latter of which will send a cold front across the area Friday into Saturday morning. Behind this low, the GFS continues to keep stationary front south of the region, whereas the EC less amplified allowing for mid- level ridge to build over southern New England. This difference has resulted in a wide temperatures spread amongst the guidance. Otherwise GFS bring stationary front well north of the Mid-Atlantic and with riding low pressure could see widespread rainfall. This seems to progressive compared to UKMET and CMC so have continued the trend with the EC keeping front and thus precip chances south of the region. DAILIES... Friday into early Saturday... Interesting weather set-up for Friday for southern New England. Potent low south of Hudson Bay will drag a cold front across the Northeast. Appears that the front will move through during the overnight hours with the a prefrontal trough approaching during the day on Friday. Guidance shows good southerly flow out ahead of approaching systems which help increase the moisture potential. CAPE values are over 1000 J/KG per the GFS and its even shown on the conservative EC. 0-6 KM shear values are also on the increase to 40 kts by late Friday afternoon. So with this amount of instability, shear and moisture with approaching pre-frontal trough cannot rule some strong thunderstorms across southern New England. This is also supported by mid-level lapse rates near 6 C/KM and High K and TT levels. Expect precip to develop from west and move eastward through the day. Anticipate showers and thunderstorms to be able to maintain themselves during the overnight hours as cold front approaches. Guidance still shows a good amount of elevated instability per MUCAPES near 700 J/KG at 06z as well as steepening lapse rapes as 850 mb temps continue to fall during the overnight hours. PWAT values will be near 1.3-1.5 inches which is 1 to 2 standard deviations above normal. Therefore believe the main threat will be heavy rain within any of the stronger storm. Still cannot rule out gusty wind and small hail. This timeframe is something to watch over the next few guidance cycles. Saturday into 4th of July... Cold frontal system will be offshore by Saturday allowing for a pleasant weekend. Still could see an isolated showers across the eastern half, especially if the front slows down. However most of the guidance shows very little mid-level moisture by 12z. Temperatures on both days will be in the low to mid 80s with very low humidity. Monday temperatures looks to be a bit tricky as EC still show mid- level ridge over the region with southwesterly flow. The GFS is still showing a more northwest flow keeping 850mb temps cooler. Because of the spread in the guidance, decided to use a model blend to split the difference. Temps on July 4th could reach into the mid to upper 80s. Luckily the humidity will be low keeping it a comfortable holiday. Tuesday and beyond... Still a spread in the guidance for Tuesday. The GFS continues to push stationary front north of the Mid-Atlantic bringing precip to the region. This is not wholly supported by the ensembles both the GEFS and ECE. Will keep a slight chance for now but believe that Tuesday will remain generally dry. Appears that temperatures will begin to increase on the Tuesday into Wednesday as 850mb temps increase ahead of next approaching system. && .AVIATION /00Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday Night/... Through 00Z...Moderate confidence. Mainly VFR, with local MVFR CIGS toward the Cape and islands. Low risk for a few strong thunderstorms this afternoon across eastern MA and northern RI. Tonight...High confidence. Mainly VFR. Localized patchy ground fog develops late at the typically prone locations. Thursday...High confidence. Mainly VFR conditions. Any lingering MVFR conditions will improve quickly to VFR after sunrise. Light and variable winds will result in local seabreezes developing. Thursday night...High confidence. VFR. KBOS Terminal...Moderate confidence in TAF, due to timing issues for showers/thunderstorms impacting terminal. KBDL Terminal...High confidence in TAF. Outlook /Friday through Monday/... Friday...Moderate confidence. Mainly VFR conditions and dry weather. Scattered showers and thunderstorms may result in brief periods of MVFR conditions. Saturday into Monday...High confidence. VFR. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday Night/...High confidence. Winds and seas will remain below small craft advisory thresholds through this period. Main concern will be for areas of fog, which may be locally dense at times this evening across the southern waters. Also, there is a low risk for an isolated strong thunderstorm this afternoon across the nearshore waters, especially toward Ipswich Bay. Outlook /Friday through Monday/... High confidence. Quiet boating weather expected. Winds and seas should remain below SCA criteria throughout the period. Could see a few gusts near 20 kts on Friday ahead of an approaching cold front. This front should cross waters by Saturday. Seas may reach 5 feet but low confidence at this time. This front will result in showers and thunderstorms, which will reduce visibilities at times. Nearshore waters on Saturday and Sunday may be a bit gusty. && .FIRE WEATHER... Hit or miss showers and thunderstorms will occur today, with another shot for thunderstorms Friday and Friday night. However, widespread perception looks to be nil over the next 7 days. High pressure and dry conditions appear to take hold of the region Saturday, lasting into next week. Specifics are still too hard to nail down, but it looks like the area will be less humid and a bit cooler but dry during this time frame. RH values could drop close to 30 percent between Sun into Wed. Winds overall appear to be light during this period. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...Air Quality Alert until 11 PM EDT this evening for RIZ006>008. MARINE...None. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Belk/Dunten SHORT TERM...Belk LONG TERM...Dunten AVIATION...Belk/Dunten MARINE...Belk/Dunten FIRE WEATHER...staff

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