Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 250756 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 356 AM EDT THU AUG 25 2016 .SYNOPSIS... High pressure moves farther offshore today. Warm and more humid conditions return ahead of a cold front Friday, which may lead to a few showers or thunderstorms. Another high pressure will bring dry and somewhat less humid weather this weekend, followed by a chance of showers and thunderstorms Monday. The forecast remains uncertain beyond Monday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... High pressure will continue to move offshore. This will mean a more persistent southwest flow today. Thinking less of a risk for a seabreeze along the east coast of MA. As the moisture increases, so will the clouds. The loss of any sunshine is expected to be offset by the advection of warmer air from the southwest. So, max temperatures mostly similar to slightly higher than Wednesday. The main issue today will be the potential for showers and thunderstorms later today. Plenty of heat and humidity will mean very good low level lapse rate. The mid level lapse rates are still expected to be poor. Combined with a seaward-moving high pressure, and that usually spells a slower arrival time for precipitation. Am thinking the majority of today will remain dry across most of southern New England. Cannot rule out a stray shower or thunderstorm late this afternoon, especially across far western MA. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/... Subtropical moisture plume moves into southern New England ahead of a cold front with precipitable water values approaching 2.00". The forcing continues to be rather weak, although mid level lapse rates should become a bit more supporting of thunderstorms. Not expecting an all-the-time washout everywhere. However, wherever showers and thunderstorms develop, there will be the possibility for a torrential downpour. Humidity continues to increase tonight into Friday. As such, temperatures tonight are not expected to drop much below 70 at most places. It will likely be muggy sleeping weather. The heat continues to build Friday. A cold front should move through or region by late Friday, which should bring an end to the rainfall chances. The humidity will take longer to drop off. && .LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/... */ Highlights... - Shower and thunderstorm chances for Monday - A cool, comfortable weekend in between - Monitoring Invest 99L, low confidence forecast into next week */ Discussion... With a negative E Pacific Oscillation and Pacific N American trend into the end of August, wanting to maintain the Atlantic High over the SE CONUS with anomalous NE CONUS ridging. Leaning more towards dampened outcomes for Monday as a cold front sweeps the NE CONUS. Depending on the timing of surface features, to which there are some subtle wobbles, there is the chance of showers and thunderstorms, though believe such chances are more N/W towards better dynamics and removed from the influence of the Atlantic ridge. There is in both cases sufficient moisture and instability (though the latter dependent on cold frontal timing and whether the boundary layer ahead destabilizes), as well as lift along the cold front and a veering wind profile, subsequent shear. But lacking is the necessary forcing, and lapse rates are abysmal. Thinking chance PoPs at most with breezy SW flow backing W/NW. Comes down to buoyancy and whatever the cold front can force of available moisture within the mostly suppressed environment. Could be an early show. Otherwise, cool and comfortable for the weekend. Likely some chilly temperatures down into the 40s for some spots given radiational cooling opportunities. Plenty of sunshine with light winds, sea-breezes along the shores. Forecast confidence drops after Monday. Deterministic guidance still struggles with the evolution of systems out of the N Pacific as well as their influence upon the broader trough pattern in the vicinity of W CONUS before shooting off N/E. Am more inclined to go with the deterministic EC paired with ensemble means, with support from the UKMET/Canadian forecast guidance. The dance between the H5 Atlantic High and Invest-99L, can comprehend the brief period in where the influence of the H5 ridge weakens allowing lower heights across the NE CONUS into Labor Day Weekend, only for the pattern to re-emerge as we go further into September. Not fully understanding nor in support of the deterministic GFS. Will leave the forecast decision- making of Invest-99L to the experts but do believe there is a fair amount of signal that wet-weather outcomes can be expected towards the later-half of the week and possibly again for the Labor Day Weekend across the NE CONUS. Whether any of this is associated with Invest-99L is highly uncertain. && .AVIATION /08Z THURSDAY THROUGH MONDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/... Today...High confidence. VFR with cigs 5-10k ft developing across western New England during this afternoon. SW gusts to 20-25 kt, especially along the S/SE coast. Tonight...Moderate confidence, mainly due to timing issues. Mainly VFR cigs, but areas of MVFR cigs possible. A few SHRA possible with isolated TSRA. Friday...Moderate Confidence, mainly due to timing issues. Scattered SHRA/TSRA, mainly across N/W portions of southern New England. Possible TEMPO MVFR-IFR impacts with any storms. Breezy S/SW winds with gusts up to 25 kts. KBOS Terminal...Will hold winds out of the S/SW with the terminal with the possibility of gusts of around 25 kts this afternoon. KBDL Terminal...S winds increasing with gusts up to 25 kts possible. Outlook /Friday Night through Monday/... Saturday into Sunday...High Confidence. VFR. Light winds. Likely sea-breezes. Winds turning E/SE Sunday, potentially breezy late. Monday...Moderate Confidence. SHRA mainly across N/W portions of S New England. Will keep it VFR. There is the possibility of TSRA. Timing of outcomes remains unclear at this time. S/SW winds, breezy with gusts up to 25 kts,backing out of the NW overnight. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday/...High confidence. Increasing S/SW winds ahead of a cold front through Friday. Seas should generally remain less than 5 feet. Cannot rule out some higher seas across the outer coastal waters, particularly tonight and Friday. The main issue will be the potential of 25 kt gusts at times, particularly near shore where better mixing should occur. Increasing risk for scattered showers and thunderstorms tonight into Friday ahead of a cold front. Southwest winds and more humid conditions could also lead to some fog across the southern coastal waters, with reduced visibility. Outlook /Friday Night through Monday/... Friday...Moderate Confidence. S/SW winds, breezy up to 25 kts. Waves building above 5 feet across the S/SE waters. Winds back late into Saturday morning out of the W/NW as a cold front sweeps the waters. Saturday into Sunday...High Confidence. High pressure, light winds, gradually veering out of the S/SE into Sunday, becoming breezy late. Waves remaining below 5 feet. Monday...Moderate Confidence. Winds turning out of the S/SW ahead of a sweeping cold front perhaps during the early portion of the day. Perhaps not too much impact due to waves but of greater interest will be the oncoming swell from Gaston. Waves in excess of 5 feet may occur late. && .CLIMATE... As we wind down August, we looked at the annual precipitation to date. As dry as we have been lately, there have actually been drier January to August periods. Here is how we rank at each of the climate sites: Boston: 1. 16.30" (1965) 12. 20.26" (2016)* 13. 20.28" (1950) 14. 20.45" (1980) Worcester: 1. 17.16" (1907) 17. 23.40" (2016)* 18. 23.46" (1923) 19. 23.50" (1999) Providence: 1. 16.84" (1957) 42. 25.83" (2016)* 43. 25.95" (1945) 44. 25.99" (1912) Hartford: 1. 16.75" (1965) 6. 22.34" (2016)* 7. 22.51" (1921) 8. 22.57" (1980) && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 2 PM this afternoon to 10 PM EDT this evening for ANZ231>237-251. Small Craft Advisory from 2 PM this afternoon to 7 AM EDT Friday for ANZ250-254. Small Craft Advisory from midnight tonight to 7 AM EDT Friday for ANZ256. && $$ SYNOPSIS...Belk/Sipprell NEAR TERM...Belk SHORT TERM...Belk LONG TERM...Sipprell AVIATION...Belk/Sipprell MARINE...Belk/Sipprell CLIMATE...Belk

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