Area Forecast Discussion
Issued by NWS Boston, MA

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787 FXUS61 KBOX 240353 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1153 PM EDT MON MAY 23 2016 .SYNOPSIS... An area of low pressure will wobble north along the coast into this evening and through Tuesday bringing with it showers and the chance of thunderstorms. Warmer weather follows beginning Wednesday. A weak front will move south of the region Wednesday night with dry, warm weather for Thursday. The front will move north toward southern New England as a warm front on Friday bringing scattered showers and thunderstorms. The front will continue to drift slowly north over the Memorial Day weekend. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... 1110 PM update... Light showers rotating westward around cutoff H5 low pressure near or just off the mid Atlc coast reaching the S coast of RI into N central and NE CT at 03Z. Looks like most of the activity will remain W of E MA and more of RI, but can not rule out widely sct showers pretty much across the remainder of the region into the early morning hours. Then, toward sunrise, will start to see sct showers pretty much anywhere as weak short wave rotates westward in the cyclonic upper flow to the south, as well as decreasing temp/dewpoint spreads especially near the coast. With the onshore wind, will see low clouds and patchy fog moving in. Would not be surprised to see some spotty drizzle as well. 18Z GFS and new 00Z NAM both continue to signal increasing instability, with total totals up to the lower 50s, surface based LIs down to zero to -2 and K indices to the lower 30s around or after 09Z. NAM appears too robust considering the lack of convection into the region, so used a blend of the GFS/NAM with a bit more weight to the GFS. Noting some CG and in cloud lightning S of 40N late tonight, but appears this will rotate S of the region for now. Have kept mention of thunder in the forecast toward daybreak into Tuesday morning, though went with isolated wording. Remainder of forecast in pretty good shape, but have updated to bring conditions current. Previous discussion... Low pressure wobbles N evolving into its dying phase undergoing occlusion. During this morphology, focus is on the crux of mid- level vortmax energy and parent weak low-level convergence rounding W-NW round the low into S coastal New England. Should see decent low to mid level forcing with some venting aloft, along the leading edge of which a band of light to moderate rain should emerge. Also isolated thunderstorms are possible given marginal instability and weak shear parent to expected lift, but such activity should be non severe with the main threats being lightning and locally heavy rain. A consensus of high-res and mos-guidance performed, confidence is for a band of activity to pivot NW across S New England settling N to S across W New England and along the high terrain. This keeps a good chunk of E/SE MA in chance PoPs. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/... Tuesday... Breaking down. Low chokes itself off entraining drier air as it stacks and undergoes occlusion within its dying phase. The trowaling and comma shape to the low persists albeit weaker seemingly over W portions of New England parent with low level convergent flow along the E slopes of high terrain and forcing per rotating mid-level vortex energy. But to the E we could see some improvement with clouds becoming broken and perhaps some hints of sunshine. Thus can not rule out partial clearing. PoPs evolving with highest confidence over the Berkshires while chance-scattered to the E/SE if forecast models are right in the evolution of drier air wrapping into the system. A lot of wiggle room and wobble with this system to which the high-res guidance is not absolutely succinct but has a decent handle on the trend. Will avoid high PoPs accordingly with the scattered to broken nature of the low. Thunder does remain a possibility with continued marginal instability and weak shear. Think isolated chances and will prevail accordingly. Cooler day with clouds in abundance and E/NE flow. Highs up into the 60s. An edge warmer to the W as conditions improve late in the day with winds shifting out of the W/NW. Tuesday Night... The end. Low continues to undergo its dying phase choking upon drier air as it peels off to the E. Comma head over the W sweeps E across S New England per a consensus of high-res forecast trends, but by this point the activity is all but scattered. Should see most of the wet weather by consensus conclude by midnight behind which W/NW flow prevails. Anticipated clearing and light winds, would expect lows to drop into the 40s, and considering the recent rains, can not rule out some dense fog development if conditions are right. && .LONG TERM /WEDNESDAY THROUGH MONDAY/... HIGHLIGHTS... * Significantly warmer and dry Wednesday and Thursday * Above average temperatures will continue Friday into Sat * Hit or miss showers with thunderstorms are possible into the Holiday weekend. OVERVIEW... Large scale pattern is in agreement with both determinisic and ensemble guidance. Upper level low will move towards the Maritimes as Midwest ridge builds into the Northeast. This ridge will bring summer-like warmth and humidity to the region as ensembles show both the 700 and 500 heights nearly 1-2 standard deviations above normal. Several waves will move through the flow keeping a chance of showers and thunderstorms in the forecast for Late Thursday into Saturday. Because of the mesoscale differences in the guidance trended the forecast towards an overall blend. DAILIES... Wednesday into Thursday...Moderate Confidence. Upper level low will push towards the Maritimes on Wednesday. However, a quick moving shortwave will try to push through the region during the day. This approaching frontal system will slow down or stall as mid-level heights begin to build across the region. Therefor, believe that an isolated shower across the higher terrain is possible but most of the day appears to be dry. Good mixing during the afternoon will help warm temperatures back to above average with highs in the low to mid 80s. This may be the first time that Boston Logan will hit 80F. The cold front weakens and stalls over the region by Thursday as ridging aloft continues. There is the potential for a spot thunderstorm especially across the CT valley and points west where the better instability will occur. So another mainly dry day is anticipated on Thursday. Temperatures will be similar to that on Wednesday with mixing up to 800mb. Will be cooler along the coastlines as a sea breeze looks to develop during the afternoon. Thursday night into Friday...Moderate Confidence. Depending on where the front stalls, we could see scattered showers and thunderstorms Thursday night into Friday. Guidance continues to hint at the possibility of a decaying MCS moving from the Great Lakes region towards southern New England. However latest trends is that this will pass closer to NH than directly over southern New England. Something to watch in the coming days. Friday, it still remains unclear how far northward the front will make it. If it stalls/remains over the region then showers and thunderstorms may continue, keeping more clouds than sun which will lower temperatures. Right now believe that the front will get through a good portion of the area allowing for temps to reach into the 80s with mid to upper 70s across the east coast. Memorial Weekend...Moderate Confidence on Saturday. Low Confidence on Sunday. High pressure south of the region will begin to strengthen on Saturday. This will continue to build the ridge to 2-3 standard deviations above normal. Saturday looks quite balmy with 925 mb temps warming close to 21-23C. This could result in highs in the mid 80s on Saturday, with a low probability of a 90F across the CT valley. For now continue with a conservative route for temperatures. These warm temperatures and lingering moisture may trigger off afternoon convection on Saturday. Low confidence on Sunday as EC wants to push a backdoor cold front through the region where the GFS brings the front through on Monday. Depending on the frontal timing, temperatures on Sunday could be in the mid 80s with sun or the upper 60s with clouds and drizzle. Will have to wait for the guidance to come in better agreement before having a better idea on how the weekend will end for southern New England. && .AVIATION /03Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Tuesday Night/... Overnight...Moderate Confidence. Mainly VFR through 04Z-06Z, except LIFR CIGS/MVFR-IFR VSBYS moving onshore from Cape Cod to along E coastal Mass. Should see MVFR- IFR CIGS/MVFR VSBYS move W to about KORH-KIJD with spotty MVFR CIGS/VSBYS across the CT valley mainly after 06Z. Scattered showers with MVFR conditions across N CT/W RI into CT valley. Isolated thunder possible after 08Z mainly near S coast. Light E-NE winds. Tuesday...Moderate Confidence. SHRA and chance TSRA continue with greatest confidence over W terminals. Widespread MVFR/IFR impacts begin to shift E with the usherance of winds backing out of the W/NW. Gusts of around 15 kts possible. Tuesday Night...Moderate confidence. Continued clearing trend W to E with W/NW winds. Improving to VFR. It is perhaps at the start of the period that MVFR/IFR will only linger along the E coast of MA. KBOS TAF...Sct showers will move across the terminal tonight and into tomorrow. Low prob for some thunder. VFR will drop to MVFR/IFR after 06z. KBDL TAF...Confident the terminal will see a fair share of -RA beginning around midnight and continuing through much of Tuesday before clearing out late. Moderate prob for TSRA. MVFR conditions after 06z. Outlook /Wednesday through Saturday/... Wednesday through Thursday...High Confidence. VFR. Thursday night and Friday... Low to Moderate Confidence. Mainly VFR...becoming MVFR. Showers and thunderstorms beginning late Thursday night lasting through Friday. Saturday...Moderate Confidence. Mainly VFR with some MVFR within in scattered shower or thunderstorm. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Overnight and Tuesday...Moderate Confidence. E-NE winds with gusts up to 15 kt mainly overnight, then diminishing Tuesday. Seas 4 feet or less. Visibility reductions in areas of fog moving W from Mass Bay and E of Cape Cod overnight, local mist as well. Scattered showers along the S coast of RI, then continue to develop across entire S coast, possibly reaching to E coastal areas by daybreak. Isolated thunderstorms after 08Z through mid morning Tuesday possible. Tuesday Night...Moderate Confidence. Winds back out of the W/NW with departure of the low. Change in wind direction against a E/SE swell, could see some wave heights up to 5 feet on the outer waters requiring small craft advisories. Aside, rain comes to an end and visibilities improve if they had not done so during the day Tuesday. Outlook /Wednesday through Saturday/...Moderate confidence. Wednesday...Seas subside into Wednesday afternoon. Light winds. Wednesday night and Thursday...Light winds from the southwest will shift to the northeast by Thu as a frontal system stalls over the waters. Seas mainly below small craft criteria but cannot rule out a few hours of 5 footers across the southeastern waters. Thursday night and Friday...Southeast winds on the order of 10-15 kt and seas 1 to 3 feet. Just a slight chance of showers or a thunderstorm. Saturday...Southwest winds will prevail with seas less than 3 feet. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Dunten/Sipprell NEAR TERM...Dunten/EVT SHORT TERM...Sipprell LONG TERM...Dunten AVIATION...Dunten/Sipprell/EVT MARINE...Dunten/Sipprell/EVT is the U.S. government's official web portal to all federal, state and local government web resources and services.