Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 161209 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 709 AM EST Fri Feb 16 2018 .SYNOPSIS...
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Showers will continue to impact Southern New England into the afternoon, followed by a return to seasonably wintry temperatures tonight into Saturday. A fast moving low pressure system will bring a plowable snow Saturday night into very early Sunday morning with the heaviest amounts near and south of the Massachusetts turnpike. A warm front will cross the region Monday afternoon and night with a period of rain showers likely. This will be followed by near record breaking warmth Tuesday and Wednesday before cooler weather returns by the end of the work week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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705 am update... A cold front slowly crosses the region today...but mid level moisture/forcing will linger resulting in periods of showers this morning along with patchy fog. These showers will likely persist into the afternoon based on the latest guidance... especially near and south of the MA turnpike as lift/forcing remain in place. Cloudy skies will also persist through the afternoon...but given very mild start high temps in the upper 40s to lower 50s are expected in most locations. A few areas may even see some middle 50s.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/... Tonight... With front finally clearing the Cape/Islands this evening, H92 temps will continue to drop, starting around -3C at 00Z, dropping to -10C by 12Z. The clearing and cold advection will lead to more seasonably cold temperatures overnight tonight. Even though by the AM hours, skies will be clear, the maintenance of strong pres gradient will allow winds to continue through the overnight hours. Therefore, ambient temps will not dip as low as they otherwise could, but with winds 10-20 mph with gusts 25-30 mph at times will allow wind chills to drop into the low teens even while 2m temps remain in the upper teens to mid 20s. Will need to monitor roadway drying, as the lingering showers and rapid cooling could allow for isolated ice development. Sat... Seasonably cool, with highs mainly in the mid 30s, but with lighter winds than the overnight hours. Although increasing moisture is expected, the bulk of any impacts will be overnight Sat night, see below for that. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
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Highlights... * Plowable snow Saturday night: Heaviest likely south of MA Pike where a Winter Storm Watch has been posted * Snow ends near daybreak Sunday with rapidly improving conditions * Warm front likely brings a period of showers Mon afternoon/night * Near record breaking warmth likely Tue and Wed Details... Saturday night... A fast moving southern stream wave will bring accumulating snow to the region Saturday night as it tracks near the Benchmark. Specific snowfall amounts remain uncertain and are dependent on the amplification of shortwave energy to our west...but higher amounts likely south of the MA turnpike. The ECMWF/UKMET are most amplified with the system and indicate the potential for a swath of 4 to 8 inches of snow...near and south of the MA turnpike. Even though temperatures in this region would be near freezing...impressive snowgrowth/frontogenesis would result in decent snow ratios. Meanwhile...the GFS/GGEM are less amplified which would keep the best forcing south of our region resulting in a 1 to 4 inch snowfall. The system is rather progressive...which will limit duration of the snow. Given its origins it will be loaded with moisture...so 1 inch per hour snowfall rates would be possible if it gets close enough to our region. Bulk of the accumulating snow looks to occur between 03z and 10z Sunday...so the timing will limit impact for motorists. The one thing will have to watch is if the higher snowfall amounts are realized. Since this will be a wet snow...the risk for isolated downed tree limbs would exist in the lower elevations. This event is still 48+ hours out in the model guidance world and a subtle change in track will have a big impact on snow accums. Given a Winter Storm Watch requires only 50 percent confidence in 6 inch amounts being reached...opted to issue one near and south of the MA turnpike. We did not include the Cape/Islands as marginal boundary layer may allow for a change to rain cutting down on snow accums. It is also possible that some rain mixes in along the south coast. However...if guidance trends colder the watch will have to be expanded to include the Cape/Islands. In a nutshell...our deterministic forecast has 3 to 6 inches north of the MA turnpike and 4 to 8 inches south of the pike /away from the Cape and Islands/. Our forecast is on the higher end of the guidance based on strong frontogenesis/snowgrowth potential south of the Pike. However...it certainly is possible that this system shifts 50 miles south and we end up with just a 1 to 4 inch snowfall. Sunday... Snow will pretty much be over by daybreak Sunday as progressive southern stream wave will rapidly be exiting the region. Rapid improvement will occur on roadways during the morning as temps quickly rise above freezing and well into the 40s Sun afternoon. This coupled with plenty of sunshine will result in a lot of the snow melting by day/s end. Monday and Monday night... A warm front will be approaching the region from the south. Enough lift/forcing with this warm front should result in a period of rain showers sometime Monday afternoon and/or night. Highs on Monday will probably be in the 40s to around 50...but steady or slowly rising temperatures possible Monday night as long as the warm front makes it through the region. Tuesday and Wednesday... Anomalous upper level ridge of 590+ decameters off the southeast coast will set the stage for near record breaking warmth Tue and Wed. Southwest flow around this powerful upper level ridge should result in high temperatures reaching into the 60s in many locations both days. In fact...if we receive enough sunshine temperatures could break 70 in a few locations on Wednesday. Thursday... Low confidence on Thursday temperatures. Some of the guidance has slowed up the passage of the cold front allowing for another very mild day. Whether or not that happens is uncertain...but even if the cold front crosses the region early temps should still be above normal.
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&& .AVIATION /12Z FRIDAY THROUGH TUESDAY/...
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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 Saturday/... Through 21Z...Moderate confidence. A wide variety of conditions early this morning from VFR to IFR in areas of fog and showers. Skies remain cloudy this afternoon...but conditions should improve to mainly MVFR-VFR. Nonetheless...the risk for showers will continue into the afternoon. After 21Z through tonight...High confidence. SHRA across SE MA ends with clearing continues from NW to SE. Timing may be off a bit in TAF, but trend is toward VFR all sites. Also, 18Z-06Z W wind gusts 25-30 kt possible at times. Sat...High confidence. Mainly VFR. Winds begin N, but then shift around to the S-SE. KBOS Terminal...Moderate confidence in TAF. KBDL Terminal...Moderate confidence in TAF. Outlook /Saturday Night through Tuesday/...Moderate Confidence. Saturday Night: IFR conditions in snow with heaviest between 3z and 10z Sunday south of the MA turnpike. Ptype may be rain at times across Cape/Islands depending on track. Sunday: VFR. Breezy. Sunday Night: VFR. Washingtons Birthday: Mainly VFR, with areas MVFR possible. Breezy. SHRA likely. Monday Night: Mainly MVFR, with local IFR possible. Breezy. SHRA likely. Tuesday: Mainly MVFR, with local IFR possible. Breezy. 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 Saturday/...High confidence. Through 21Z... Winds will gradually shift to the W later this morning into the early afternoon, but with gusts below 25 kt. Building S swell continues, with 5-9 ft seas possible through the morning across the S waters, requiring Small Craft Advisories. Rain/fog lead to reduced vsbys. After 21Z and tonight... W winds increase as skies clear during the evening and overnight. Gusts to 35 kt expected mainly across the E waters with mainly 30 kt gusts across the S waters. Gale Warnings continue, along with Small Craft Advisories elsewhere. Sat... Winds and seas slack, especially as the winds shift to the S-SE. Small Craft Advisories will end through the morning. Outlook /Saturday Night through Tuesday/...Moderate to High Confidence. Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Rain, snow. Areas of visibility 1 nm or less. Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas locally approaching 5 ft. Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Washingtons Birthday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers. Monday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Rain showers likely. Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Slight chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Winter Storm Watch from Saturday evening through Sunday morning for CTZ002>004. MA...Winter Storm Watch from Saturday evening through Sunday morning for MAZ011>013-015>021. RI...Winter Storm Watch from Saturday evening through Sunday morning for RIZ001>007. MARINE...Small Craft Advisory from 6 PM this evening to 6 AM EST Saturday for ANZ232. Small Craft Advisory from 5 PM this afternoon to 5 AM EST Saturday for ANZ230-233-234. Gale Warning from 6 PM this evening to 2 AM EST Saturday for ANZ231-251. Small Craft Advisory from 4 PM this afternoon to 1 AM EST Saturday for ANZ236. Small Craft Advisory until 7 AM EST Saturday for ANZ235-237. Gale Warning from 6 PM this evening to 3 AM EST Saturday for ANZ250-254. Small Craft Advisory until 10 AM EST Saturday for ANZ255-256. && $$ SYNOPSIS...Frank/Doody NEAR TERM...Frank/Doody SHORT TERM...Doody LONG TERM...Frank AVIATION...Doody/Frank MARINE...Doody/Frank

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