Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 231958 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 258 PM EST Thu Nov 23 2017 .SYNOPSIS...
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Quiet weather through Friday with dry and cool conditions. Milder air returns Saturday ahead of a cold front. That cold front swings through Southern New England late Saturday and early Saturday night. Blustery and cooler weather follows Sunday. Conditions trend toward dry and milder again Tuesday and Wednesday, and then cool again Thursday behind another cold front.
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&& .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 10 am update... Happy Thanksgiving! Cold air advection proceeding ushered by NW winds, breezy over the waters especially with gusts up around 20 mph. Over the warmer waters, marine stratus, but remaining off- shore, all of S New England mostly clear other than some mid to high clouds sweeping in ahead of a weak trof disturbance that is approaching from the W. Main weather feature to watch today, will likely see increasing clouds over N/W areas of MA and CT with all other areas remaining under abundant sunshine. Winds diminishing becoming W with very little change in the airmass aloft, looking at highs around the low 40s, roughly 5 to 10 degrees below normal. Dry weather. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Trough axis will push through the region this evening and slide to the north tonight. Mid to high level clouds will stream through as guidance continues to show some moisture for the first half of the night. 925mb jet will be on the increase along the passing wave resulting in a few gusts during the overnight hours. Best location is along the shoreline where waters will help increase the mixing. While the jet could limit radiational cooling, expect overnight inversion to limit the mixing across the interior. Aside from the cloud cover, dry weather will prevail. Expect temperatures in the mid 20s with metro region in the low 30s. High pressure will allow for dry weather once again on Friday. Developing ridge aloft will result in a more southerly flow. This will help push temps to be warmer than today. Highs should reach into the upper 40s to low 50s. && .LONG TERM /SATURDAY THROUGH THURSDAY/...
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Big Picture... Longwave scale shows a broad trough along the USA East Coast and West Atlantic, a second trough over the Eastern Pacific, and a ridge over the the Plains. The Eastern trough lingers much of the week while the overall flow trends zonal. Model consensus shows northern stream shortwaves crossing New England Saturday night/Sunday and again Wednesday. The models also show a southern stream low crossing the Southeast USA Thursday trailing the Wednesday northern shortwave. The mass and thermal fields are similar through Mon night/Tuesday, but then diverge by showing different timing of the northern and southern stream features. The feature that becomes the northern and southern shortwaves next week is currently over the Aleutians and diving south over the Pacific Ocean...and it reaches the USA West Coast by Monday. Expect changeable solutions regarding this feature until that time. Contour heights and thermal fields are a little above normal Saturday, trend colder than normal Sunday-Monday, then trend above normal midweek next. Details... Saturday... Low pressure passes well offshore. General agreement that the southern shortwave remains unphased with the northern trough. Meanwhile, the northern trough doesn`t dig much until the offshore low is moving past us. So expect the precipitation to remain over the ocean. Cold front approaches during the afternoon and passes through Southern New England during the evening/early night. Moisture is limited below 700 mb much of the time, but runs deep briefly during the evening. Precipitable water values climb to about 0.85 inches during the evening, which is above normal for late November. We will show low-end chance pops during the late afternoon/evening. Temps in the mixed layer are forecast at 850-mb equiv of -1C to -4C, so expect max sfc temps in the 50s. Behind the front, the airmass cools and dries slowly, so min temps at night should only fall to the 30s and low 40s. Sunday-Monday... Upper trough digs over New England Sunday. Cold pool will be in place with 500-mb temps at -28C working to destabilize the airmass. Moisture lingers below 800 mb during this time. Expect quite a few clouds to pop during the day, but moisture is too limited for showers. Mixed layer temps will support max sfc temps in the upper 30s and 40s. The trough moves off on Monday and high pressure builds surface and aloft. Expect a fair day with max sfc temps in the 40s. Tuesday through Thursday... Another cold front crosses us midweek, driven by the northern stream shortwave. As noted above, there are timing uncertainties among the models, so we used a blend. This favors a Wednesday passage at this time, but the uncertainties noted above may change that exact timing. This will need to be monitored. The blend of model data supports slight chance pops Wednesday with the cold fropa and mainly dry Thursday.
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&& .AVIATION /20Z THURSDAY 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 Friday Night/...High confidence. Today and tonight... VFR with W to NW winds through the period. Friday... VFR with winds backing to the south, but remaining light. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Saturday through Tuesday/... Saturday through Saturday Night: Mainly VFR, with local MVFR possible in showers late afternoon and night. Breezy. Slight chance SHRA. Sunday: VFR. Windy with local gusts to 30 kt. Sunday Night through Tuesday: VFR. Breezy.
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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 Friday Night/... Decided to cancel the Small Craft Advisory for Cape Cod Bay as recent observations indicate wind gusts are less than 25 kt. Buoy in the bay also showed wave heights less than 5 feet. Previous Discussion... Winds shift to the W, with gusts generally remaining below 20 kt after sunrise. Seas however will take some time to fully diminish, and will require small craft advisories to linger much of the day. Winds will shift to a more southerly direction on Friday and will begin to increase during the evening. Advisories for the ocean waters have been extended for the outer waters into tomorrow given 5 ft lingering swells are expected. Outlook /Saturday through Tuesday/... Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft. Saturday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Sunday Night: Winds less than 25 kt. Local rough seas. Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Monday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 7 PM EST this evening for ANZ250. Small Craft Advisory for hazardous seas until 7 AM EST Friday for ANZ254>256.
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&& $$ SYNOPSIS...WTB/Dunten NEAR TERM...Belk/Dunten/Sipprell SHORT TERM...Dunten LONG TERM...WTB AVIATION...WTB/Dunten MARINE...WTB/Dunten

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