Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 160232 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1032 PM EDT Sun Oct 15 2017 .SYNOPSIS...
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A strong cold front sweeps across the region overnight and will bring scattered showers into early Monday morning. Behind the front, it turns sharply cooler and brisk Monday afternoon with temperatures dropping down close to freezing by daybreak Tuesday. Gradual warm up through the week, possibly into the weekend, while overall dry and quiet with scattered cloud decks and breezy winds from time to time.
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&& .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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1015 PM Update... Line of showers continues progress SE out of NY state, reaching the northern Berkshires at 02Z. Noting gusty SW winds along the southern near shore waters. Gusts up to 32 kt at KEWB, 34 kt at KFMH and 32 kt at KPVC, with a peak wind of 35 kt at KPYM and 31 kt at KCQX. Also noting gusts to around 30 kt across portions of E Mass into RI, so very good low level mixing continues this evening. Noting the showers ahead and along the approaching cold front have been tending to slowly weaken, but bands of stronger reflectivity still seen. Short range and high res models do continue the trend of weakening this line further as it crosses the region overnight. Near term forecast pretty much on track so far with temps mainly in the mid-upper 60s across the region, which will remain steady through around 06Z or so, then will fall pretty quickly as the cold front pushes across through the remainder of the night. Previous Discussion... As the fine-line progresses E there less instability to work with. However riding the cold front along and ahead of which the activity is maintaining is stout. A very fine thermal discontinuity met with a decent pressure couplet as discerned from the latest SPC / high- res mesoanalysis. A lot of frontogenetical convergence along the line that with heavier precipitation outcomes coupled with both the isallobaric and gradient winds is lending to mechanical mix-down of very fast westerly winds, in excess of 40 mph observed over the E Great Lakes Region. Some question as to the inversion over our region and a limited threat, however RAP sounding profiles highlight that along the front the inversion is somewhat eroded. In all, the expectation is for the fine-line to weaken, but closely keeping an eye give the associated synoptics. Expect the cold front to sweep across after midnight, and could see winds amplify with a brief period of 35 to 45 mph gusts, more likely behind the cold front out of the W/NW.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/... Monday... A few left over showers will be possible across the far SE New England coast during the first part of Monday morning. Otherwise, expect some strato-cumulus to work into the region in the cool advection pattern but will also see some peeks of sunshine. Temperatures late Monday morning and afternoon will mainly be in the upper 50s to the lower 60s, but a bit cooler in the higher terrain. Northwest wind gusts of 20 to 30 mph will make it feel chilly compared to our recent mild weather. Monday night... High pressure will build in from the west allowing winds to gradually diminish, except across the southeast New England coast. Cool airmass in place should allow overnight low temps to drop to around 30 to the lower 30s in the normally coolest outlying locations. Some frost/freeze headlines will likely be needed where the growing season is technically still in place. Lastly, it will be milder across the Cape/Nantucket as NNW winds will result in ocean effect cloudiness and holding low temps in the 40s. 850T to seas surface temperature differential around 20C may even yield an isolated shower or two. && .LONG TERM /TUESDAY THROUGH SUNDAY/...
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*/ Highlights... - Gradual warm-up through the week into the weekend - Perhaps a pattern change into late October, more active, cooler */ Overview and Discussion... Change is on the horizon. A deeper polar low upstream shifting from the Siberian Peninsula E into Alaska diminishes downshearing storm development over the W CONUS and rather promotes ridging into late October. Concurrent with a strong MJO phase 4/5/6 signal, and the expectation is for mild, moist Pacific air to pump into the W CONUS ahead of deep troughing over the NE Pacific. Meanwhile this also promotes downshear deeper troughing over the E CONUS. But prior to, as the polar low matures E into Alaska, individual upstream Pacific origin waves continue to slam into the Cascades later emerging downstream and undergoing cyclogenesis NE into Canada. High pressure is promoted over the SE CONUS beneath preferred H5 ridging. Subsequent SW pump of warmer air across the Central into E CONUS as far N/E into NE Canada. Looking at a suppressed environment over S New England. Aside from a series of weak frontal passages concurrent with breezy winds, Tuesday night into Wednesday, and again Thursday night into Friday with light shower activity over N New England high terrain, otherwise little to no wet-weather activity given abundant dry air through the following weekend. Main story is the warming temperature trend for late October beginning near- seasonable with highs around the low to mid 60s warming into the 70s, possibly into the 80s by the weekend. Consensus of model guidance preferred which signals the low to mid level high situated over the SE CONUS out to Bermuda round which the heat pump flows, breaking down early next week as Pacific energy shears off into the SW CONUS as high pressure builds around the coast of CA. The pattern flips and troughing becomes promoted into the NE CONUS. Looking at the next cold frontal passage and chance of wet weather potentially beginning around Monday night into Tuesday.
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&& .AVIATION /02Z MONDAY THROUGH FRIDAY/...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. Overnight... MVFR-IFR CIGS linger over SE terminals, with SCT-BKN clouds around 2-3Kft elsewhere. Mainly VFR VSBYS across the region. SW wind gusts up to 30 to briefly 35 kt along the S coast, Cape Cod and the islands and 20-30 kt elsewhere. Expect winds to quickly shift to W-NW with the frontal passage. Could see brief gusts up to around 35 kt or so with the front. A line of SCT SHRA will push across the terminals ahead of the cold front which should push offshore by around 09Z or so. Monday... SCT SHRA ending. SW winds turning W/NW. CIGs improving, BKN to SCT low-end VFR. Low risk MVFR early. Gusts around 20 to 25 kts. Monday night... VFR other than perhaps a period of some marginal MVFR ocean effect clouds across the Cape/ACK. Winds diminish for most but NW wind gusts of 20 to 25 knots continue for Cape/Islands. KBOS Terminal...Strongest winds developing and likely to continue towards midnight. Already gusts in excess of 30 kts. Will push higher around 35 kts for tonight. KBDL Terminal...SW wind gusts increasing. Expect strongest winds at the beginning of the TAF period going into midnight. Monitoring the fine-line W which will move into the terminal close to 10p behind which winds revert NW continuing into the early morning hours Monday, remaining gusty but around 20 kts. Outlook /Tuesday through Friday/...Moderate confidence. Tuesday through Friday... VFR. W winds. Breezy at times, around late Tuesday and again late Thursday
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&& .MARINE...
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Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday Night/...High confidence. Overnight... SW winds gusting up to 25-30 kt will continue overnight, with brief gale force gusts across the southern near shore waters especially Buzzards Bay, Vineyard Sound and Nantucket Sound as well as the eastern open waters through around midnight. Small crafts continued for all waters. Scattered showers move across the waters after 06Z or so with the cold front. Winds quickly shift to W-NW with the frontal passage mainly across the eastern waters around 07Z-09Z Monday and Monday night... Behind the sweeping cold front, NW gusts 20 to 30 kts, close to near gale force, especially over the open waters. Strongest winds immediately behind the front and then into Monday night given colder air aloft building S over the warm waters. SMALL CRAFT ADVISORIES continue and may need to be extended. Outlook /Tuesday through Friday/...Moderate confidence. Overall W winds, breezy at times around late Tuesday and again late Thursday. Waves for the most part below 5 feet, only issues worth noting are on the S/SE outer waters early Tuesday, possibly again Thursday night into Friday. Otherwise good boating weather.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until noon EDT Monday for ANZ231>235-237- 251. Small Craft Advisory until 8 AM EDT Monday for ANZ230-236. Small Craft Advisory until 8 AM EDT Tuesday for ANZ250-254>256.
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&& $$ SYNOPSIS...Frank/Sipprell NEAR TERM...Sipprell/EVT SHORT TERM...Frank LONG TERM...Sipprell AVIATION...Frank/Sipprell/EVT MARINE...Frank/Sipprell/EVT

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