Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 152317 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 717 PM EDT Sun Oct 15 2017 .SYNOPSIS... A strong cold front sweeps across the region overnight and will be accompanied by 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. && .NEAR TERM /UNTIL 6 AM MONDAY MORNING/...
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7 pm update... Fine-line progressing quickly across the NE CONUS ahead of which SW flow is increasing presently with the pressure gradient and subsequent low-level jet. Already gusts observed over S New England in excess of 30 mph and have updated gust forecast accordingly. 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. Echoing prior forecasts, expect SW wind gusts around 20 to 30 mph ahead of the cold front getting into S New England 10p to midnight. The cold front sweeping 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. SPECIAL WEATHER STATEMENT continues for W areas of CT and MA for the threat of strong winds with the sweeping cold front. A few weakened trees and/or tree limbs may be knocked down if this occurs. Temperatures remaining stable in advance of the cold front in the 60s, dropping off with passage. Weak line of showers sweeping with the cold front. DENSE FOG ADVISORY for the Islands. Fog issues should clear up over the next couple of hours, perhaps earlier, as SW winds increase and erode the low visibility.
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&& .SHORT TERM /6 AM MONDAY MORNING THROUGH MONDAY NIGHT/...
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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.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/... */ 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 up- stream 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. && .AVIATION /00Z 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. Tonight... MVFR-IFR CIGs lingers over SE terminals. Low-end VFR elsewhere. FG remains an issue over the Outer Cape and Islands, eroding after midnight. This as a line of SHRA sweep the terminals ahead of which SW winds gust around 20 to 30 kts, as they are presently, potentially as high as around 35 kts, turning out of the W/NW into morning. SHRA moving in 2z-6z (10p-2a). Stronger winds possible with the line of SHRA, monitoring closely impacts across Upstate NY, but the severe threat is expected to dampen slightly into S New England terminals. Again, re-emphasizing the threat of gusts around 35 kts. 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. Tonight... SW gusts 25 to 30 kts overnight ahead of a sweeping cold front towards morning. Brief near or at gale force gusts possible especially this evening ahead of the approach cold front, more importantly over the E waters. Ever brief, held with SMALL CRAFT ADVISORIES for all waters with amended wording for the brief period of gales roughly 8p to midnight. 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... CT...None. MA...Dense Fog Advisory until 10 PM EDT this evening for MAZ023-024. RI...Dense Fog Advisory until 10 PM EDT this evening for RIZ008. 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. && $$ SYNOPSIS...Frank/Sipprell NEAR TERM...Frank/Sipprell SHORT TERM...Frank LONG TERM...Sipprell AVIATION...Frank/Sipprell MARINE...Frank/Sipprell

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