Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
-- Highlight Changed Discussion --
-- Discussion containing changed information from previous version are highlighted. --
000 FXUS61 KBOX 300138 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 937 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/... 935 pm update... Cold front working across eastern MA and RI this evening. While MLcapes still remain over 1000+ j/kg in this region, it appears too dry in the mid levels to warrant any additional shower/t-storm activity. Therefore, dry weather should prevail overnight as the cold front clears the southeast New England coast. Main issue this evening is across the outer Islands and especially Nantucket where a dense fog advisory is in effect. This a result of light/moist southwest flow ahead of the cold front. Should see visibility improve after midnight from west to east as drier air works in behind the front. Low temps should bottom out mainly in the upper 50s to the lower 60s. May even see some middle 50s across portions of western MA. Patchy ground fog may develop toward daybreak in the typically prone locations, but should be short-lived. && .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 EC. 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 /01Z 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/... Tonight...High confidence. Mainly VFR, except for this risk of localized patchy ground fog late in the typically prone locations. The exception is across the outer Islands and portions of the Cape, where some low clouds and dense fog were affecting the region ahead of the cold front. Conditions should gradually improve after midnight as drier air works in behind the front. 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 tonight across the southern waters. 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...Dense Fog Advisory until 2 AM EDT Thursday for MAZ024. RI...Air Quality Alert until 11 PM EDT this evening for RIZ006>008. MARINE...None. && $$ SYNOPSIS...Belk/Dunten NEAR TERM...Frank SHORT TERM...Belk LONG TERM...Dunten AVIATION...Frank/Belk/Dunten MARINE...Frank/Belk/Dunten FIRE WEATHER...Dunten

USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.