Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 250229 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1029 PM EDT WED AUG 24 2016 .SYNOPSIS... High pressure moves offshore through Thursday. Warm but more humid conditions return ahead of a cold front late Thursday into Friday which may lead to a few showers or thunderstorms. Another high 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, but there`s the chance for wet-weather later in the week and possibly on into Labor Day Weekend. This as we continue to monitor the latest with Invest- 99L. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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No major changes to the forecast this evening. Still need to watch the fog potential. Thinking it will be isolated at most, and mainly in the river valleys. Brought the forecast back in line with observed trends. Previous discussion... High pressure shifting off to the SE as a cold front approaches from the N/W. Isallobaric response has allowed for winds to become S/SW yielding a moderation in the airmass with rising dewpoints. Considering increasing high clouds through this evening as winds become light, this may squash fog potential overnight. Clouds may act as a blanket to limit radiational cooling. There`s not a lot of signal to support fog potential, nor local in-house tools. Nevertheless there is a low risk of fog mainly focused within the CT River Valley. Possibility of visibilities down to a mile or so as lows dropping into the upper 50s to low 60s. May have to monitor this closely should conditions turn out clear and calm lending to effective radiational cooling. Temperatures could drop below the dewpoint during max-heating earlier today.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/... Thursday... As high pressure continues to drift offshore, leading edge of higher theta-e air moves into the region from the west with deeper moisture plume approaching. This will lead to more clouds, especially in the west during the afternoon but weather should continue. Axis of instability remains across upstate NY and northern New Eng where best chance of any convection but can`t rule out an isold shower/t-storm in western MA late in the day as higher theta-e air moves in and KI increase into the 30s. 925 mb temps 20-22C support highs in the mid/upper 80s, but cooler along the south coast with gusty sw flow. In fact, soundings suggest gusts around 25 mph in the coastal plain in the afternoon. More humid conditions as dewpoints climb into the 60s. Thursday night... Subtropical moisture plume moves into SNE ahead of a cold front with PWATS increasing to near 2" along with deep layer theta-e ridge axis. Synoptic forcing is weak but favorable moisture combined with weak QG forcing and modest low level jet along with marginal elevated instability supports a few showers and possibly a thunderstorm. A warm and humid night with lows in the upper 60s to lower 70s and dewpoints increasing to 65-70. && .LONG TERM /FRIDAY THROUGH WEDNESDAY/... */ Highlights... - Shower and thunderstorm chances for Friday and 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 both Friday and Monday as a pair of cold frontal boundaries sweep 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 for both time periods. 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 /02Z 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. VFR. Light S/SW winds. Low risk for patchy MVFR-IFR fog / low cigs mainly in the CT River Valley. SCT high cigs at times. Thursday...High confidence. VFR with cigs 5-10k ft developing in W New England during the afternoon. SW gusts to 20-25 kt especially along the S/SE coast. Thursday night...Moderate confidence. Mainly VFR cigs, but areas of MVFR cigs possible. A few SHRA possible with isolated TSRA. KBOS Terminal...Will hold winds out of the S/SW with the terminal with the possibility of gusts of around 25 kts Thursday afternoon. KBDL Terminal...S winds increasing into Thursday with gusts up to 25 kts. Outlook /Friday through Monday/... Friday...Moderate Confidence. SHRA/TSRA, mainly across N/W portions of S New England. Possible TEMPO MVFR-IFR impacts with any storms. Timing of outcomes remains unclear at this time. S/SW winds, breezy with gusts up to 25 kts, backing out of the NW overnight. 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 Thursday Night/...High confidence. 7 pm update... Increasing S/SW winds through Thursday with the likelihood of gusts up around 25 kts across the inter waters. May need to extend small craft advisories which are presently in place for the afternoon period. Wave heights up to 5 feet forecast over the E waters but can not rule out similar conditions over the S waters. Breezy conditions along with the chance of showers will persist into the evening and towards Friday morning ahead of an approaching cold frontal boundary. Outlook /Friday 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. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 2 PM to 10 PM EDT Thursday for ANZ231>237-251. Small Craft Advisory from 2 PM Thursday to 4 AM EDT Friday for ANZ250. && $$ SYNOPSIS...KJC/Sipprell NEAR TERM...Belk/KJC/Sipprell SHORT TERM...KJC LONG TERM...Sipprell AVIATION...KJC/Sipprell MARINE...KJC/Sipprell

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