Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 151756 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1256 PM EST Wed Nov 15 2017 .SYNOPSIS... Dry but chilly weather will continue through tonight. A cold front approaches Thursday as low pressure develops on the front across southeast Massachusetts. This will bring a period of rain, heavy at times to the region. Behind the departing low, blustery and noticeably colder conditions overspread the area Friday. Another low pressure area will bring milder conditions with showers and gusty winds late Saturday into Sunday morning. Dry and colder conditions push in early next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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1255 pm update... High pressure over the Canadian Maritimes has brought a scattered to broken deck of clouds in off the ocean across eastern MA/RI, with even a sprinkle or two across the outer- Cape/Nantucket. Across the rest of the region, skies were mostly sunny. Little change in our weather is expected over the next several hours with temps mainly in the middle to upper 40s through late afternoon.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/... Updated 345 AM... Tonight... Temps likely fall fairly quickly with sunset given surface ridge remains over the area combined with a dry airmass and mostly clear skies especially away from the south coast where clouds may linger. Then temps level off or even rise toward daybreak as low level flow becomes southeast and clouds quickly increase later in the evening and especially after midnight as WAA commences ahead of approaching short wave. Precip may break out between 09z-12z especially across western-central MA into CT. If precip arrives a bit earlier it may begin as a brief period of snow and/or sleet in western/northern MA. Otherwise ptype will be rain. Dry weather may linger until sunrise Thu across RI and eastern MA, with rain possibly arriving after sunrise Thu here. Thursday... Vigorous but progressive negative tilt short wave trough moves across the area Thu afternoon. This induces rapid developing secondary/triple point low along the south coast of RI/MA then into the Gulf of Maine Thu evening, with rapid falling pres of at least 1 mb per hour! However the system remains an open wave as it tracks across our region and doesn`t close off until somewhere over downeast ME. Thus the brunt of this storm will be felt northeast of our region, across NH and ME. However there will be at least some impacts here as comma head develops over southern New England. All model guid suggest a period of moderate to heavy rain in the comma- head across interior CT-MA Thu afternoon. Mid level lapse rates approach 7C/KM as comma-head develops. Thus have inserted chance of elevated convection. This may yield a period of heavy rainfall with a low risk of minor poor drainage/street-highway flooding. Other concern will be developing low level S-SE jet in the prefrontal environment. This may result in a period of strong winds in the warm sector across the south coast including Cape Cod and the Islands, with dew pts climbing into the 50s and easing low level inversion for wind transfer especially in heavy showers. Fairly strong pressure rise-fall couplet accompanying the rapidly developing secondary/triple point low. This will enhance the isallobaric wind component and increase risk for a brief period of strong winds. Will have to watch this system closely and later model trends. If secondary low develops quicker/sooner, greater the impact for southern New England. Conversely, if system develops later less impact for our region. && .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/... Highlights... * Continued progressive mid level steering flow across the lower 48 through most of it all of the long term * Strong low pressure develops Thu night/Fri as it exits to the Gulf of Maine and Maritimes with period of strong winds * Another strong low pushes into southern Quebec Sat into Sun, associated cold front moves offshore Sun * Generally dry conditions early next week Overview... General fast H5 steering flow across the northern hemisphere continues into early next week. Noting one system that pushes N of New England this weekend which tries to develop cutoff H5 low pressure, but not seeing any blocking features in this pattern. Also noting fluctuating temp trends, with cold air insurgence as low pressure centers move east of the region, followed by return to near or a bit above normal temps as next system in the flow approaches. Overall, used blend of available guidance to develop long term forecast. However, timing issues ensued amongst the 00Z model suite, with the GFS tending to be a fast outlier with the weekend system. Used a non-GFS blend for this system. Otherwise, went with overall blend of model guidance with some tweaking for timing. Details... Thursday night-Friday... As primary low pres moves into Quebec, a secondary low forms across the region late Thu, but pushes quickly NE into the Gulf of Maine Thu night into Fri. Noting good instability moves across early Thu night, so kept mention of chance thunder in the forecast, mainly across E Mass mainly near and N of the Mass Pike until about midnight. As colder air wraps in behind the system, will see some light snow showers develop mainly across the E slopes of the Berkshires before ending by around midnight. Noting strong cyclogenesis as the low moves into Mass Bay and the Gulf of Maine overnight into Friday. Strong low level NW jet also moves across, so will see gusty W-NW winds develop after 06Z or so especially along the coast. On Friday, expect gusts up to 30-35 kt along the shore, possibly up to 40 kt across the outer Cape and Nantucket. Colder air moves in, so highs will only reach the upper 30s across the higher inland terrain, ranging to the lower-mid 50s across the coastal plain. Will need to monitor for possible wind advisories across portions of Cape Cod and the islands late Thu night into Fri morning. Saturday-Sunday... N-S longitudinal high pressure progresses eastward with fast flow aloft. As the high breaks down across the region, the next low will head NE bringing another area of showers as milder air works in with increasing S-SW winds. The low deepens as it moves NE into Quebec by Sat night, so will see gusty SW winds along the S coast. Expect the cold front to move across the region late Sat night into Sun morning as winds shift to W. Gusty winds will develop after midnight Sat night into mid morning Sunday as the front moves through especially near the coast. Expect drier conditions to quickly move across by midday Sunday with gusts up to 25-30 kt along the S coast, Cape Cod and the islands, and 20-25 kt elsewhere. Expect temps close to seasonal normals both Sat and Sun. Monday-Tuesday... Expect dry conditions and chilly temps on Monday as high pressure settles across SE U.S. Cold NW winds remain in place most of the day, so expect highs to run around 10 degrees below seasonal normals. The northern portion of the ridge will break down as a weak front works across southern Canada on Tuesday, though winds become SW so it will be a milder day with highs close to normal for late November. && .AVIATION /18Z WEDNESDAY THROUGH MONDAY/...
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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 Thursday/... This afternoon and evening...Moderate to high confidence. Mainly VFR, but some marginal brief MVFR CIGS may impact eastern New England at times. Late Tonight...Moderate to high confidence. MVFR conditions should overspread much of the region after midnight. Some rain showers should arrive toward daybreak across the interior. Thursday...Moderate to high confidence. Low end MVFR to IFR conditions will dominate. Scattered showers anticipated, with a brief period of heavy rain possible between 18z and 22z. Greatest risk for a short period of heavy rain will be across RI/SE MA where a few embedded t-storms along with gusty southeast winds shifting to the west will be possible. Thursday night...Moderate to high confidence. CIGS improve to marginal MVFR-VFR. NW wind gusts of 25 to 30 knots develop during the evening with a few gusts up to 35 knots possible. KBOS Terminal...Moderate to high confidence in TAF. Mainly VFR into this evening but some marginal MVFR conditions can not be ruled out. Greater risk of MVFR conditions arrive toward daybreak. KBDL Terminal...Moderate to high confidence in TAF. VFR into this evening with MVFR conditions holding off until near or after midnight. Outlook /Thursday Night through Sunday/...High confidence. Friday and Friday night: VFR. Windy with gusts to 30-35 kt mainly near the coastal terminals. Saturday: Breezy. SHRA likely. Slight chance FZRA across N central and W Mass early. Saturday Night: Windy with local gusts to 30 kt. SHRA. Sunday: Windy with a few gusts to 30 kt. Slight chance SHRA.
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&& .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Thursday/... 645 AM update... Today... N-NE winds at 15 kt or less. Seas linger at around 5 ft on the eastern outer waters. Dry conditions and good vsby prevail. Tonight... High pres moves offshore so light SE wind develops. Dry weather and good vsby gives way to risk of showers toward daybreak. Thursday... Rapidly intensifying low pressure moves from the RI/MA south coast to Gulf of ME. SE gales possible on the front end Thu then NW gales on the back end Thu night. Isolated thunder possible. Vsby lowers in widespread showers. Outlook /Thursday Night through Sunday/... Thursday Night and Friday: Moderate risk for gale force winds with gusts up to 35 kt. Rough seas up to 10-11 ft. Chance of rain showers Thu night into early Fri. Friday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Saturday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Seas locally approaching 5 ft. Chance of rain showers. Saturday Night: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Rain showers likely. Sunday: Low risk for gale force winds with gusts up to 35 kt. Areas of rough seas. Chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Gale Watch from late Thursday night through Friday evening for ANZ230>234-250-251-254-255. Gale Watch from Thursday evening through Friday afternoon for ANZ235>237-256. Small Craft Advisory for hazardous seas until 8 PM EST this evening for ANZ250-254-255. && $$ SYNOPSIS...Nocera/EVT NEAR TERM...Frank SHORT TERM...Nocera LONG TERM...EVT AVIATION...Frank/EVT MARINE...Nocera/EVT

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