Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 220857 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 457 AM EDT WED JUN 22 2016 .SYNOPSIS...
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A few showers and maybe a rumble of thunder are possible across the Connecticut valley into northeast Massachusetts as low pressure passes across northern New England today. A warm front will approach from the south tonight, then low pressure will bring showers as it passes across the islands on Thursday. High pressure builds over the region Friday through Monday bringing a spell of dry weather. An approaching cold front may bring showers by Tuesday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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While the cold front that pushed across the region on Monday has stalled south of the area, scattered showers continue to linger across the south coast of Cape Cod as well as Nantucket and Martha`s Vineyard early this morning. A couple of brief thunderstorms passed south of Nantucket around midnight, but have pushed offshore. May see a few more showers through daybreak across the islands, then will dissipate. Short range models continue to signal a potent H5 short wave that will move across northern New England today, which is also associated with a cold pool aloft. The southern extent of this wave will swing into the CT valley this morning, bringing scattered showers. As the short wave rotates across in the fast flow aloft, the showers will move quickly E across N central and NE Mass through early this afternoon. Expect the showers to push offshore by mid to late afternoon as the short wave exits to southern Maine and Nova Scotia. Noting some marginal instability associated with the short wave, with K indices around 30 and LIs around zero, along with the cold air so can not totally rule out a quick rumble of thunder or two mainly N of the Mass Pike. Have mentioned isold thunder with those showers into this afternoon. Expect highs to range from the mid to upper 70s N of the Mass Pike to the lower 80s along the S coast with light W winds in place.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...
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Tonight... A weak high pressure ridge will build across tonight. As this moves quickly through, the stalled front to the south will begin to return as a warm front but will linger near the S coast overnight. Will see mid and high clouds increase overnight as the next fast moving system approaches. Should remain dry through the night. Temps will bottom out in the 50s. Thursday... Another short wave in the fast flow aloft will quickly shift E. Weak surface low will move along the front, which will bring showers. The best shot for showers will occur near and south of the Mass Pike. Decent PWATs associated with this system, on order of 1.5 to 1.7 inches. QPF amounts around 0.5 to 0.6 inches, so could see brief locally heavy rainfall for a time around midday across RI/SE MA. Best instability mainly offshore so not expecting convection at this time. Precip should start to taper off across the E slopes of the Berkshires by sunset. With the clouds and rain, temps will run about 5-10 degrees below seasonal normals. Readings will only top off in the lower-mid 70s, though may remain in the upper 60s along the outer Cape and Nantucket as well as the E slopes of the Berkshires.
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&& .LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...
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Big Picture... Longwave scale shows a persistent trough in Eastern North America and ridge over the West. Shortwave scale shows high pressure building over New England Friday and slipping east over the weekend. A shortwave originating over the Pacific Northwest approaches through the Great Lakes Monday and Tuesday. The upper trough suggests temps Friday a little below seasonable. But with a building ridge aloft and a developing Southwest flow at the surface over the weekend temps should trend to warmer than normal. Model forecast mass fields are similar through the weekend, then diverge a little early next week. This encourages confidence in the forecast through the weekend, then somewhat lower confidence Monday and Tuesday. Details... Thursday night through Monday...Moderate to High confidence. Offshore low pressure moves off to the east and high pressure builds in at the surface. This should bring drier air to the region and a clearing trend. Light flow on Friday suggests afternoon sea breezes on all coasts. As the high shifts east Saturday the pattern becomes less favorable, but the flow remains light and so sea breezes are still possible. By Sunday the high is well offshore and flow over New England is more southwest. Temps aloft at 10-13C Friday climb to 13-16C Saturday and 16-18C Sunday and Monday. Max surface temps should climb through the 80s during this period with low 90s possible in the warmer places especially on Sunday and Monday. Monday night-Tuesday...Low to Moderate confidence. Upper shortwave approaches, driving a surface cold front toward New England. Models show some difference in timing of these features with the GFS faster than the ECMWF. The GFS brings measurable pcpn into Western and Central sections late Monday night while the ECMWF loses pcpn Monday night and then redevelops it over New York Tuesday. We will feature slight chance pops west of Worcester late Monday night and chance pops Tuesday.
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&& .AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
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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/... Through 12Z...Moderate to high confidence. Mainly VFR conditions, though local MVFR vsbys on the outer Cape and Nantucket in patchy fog. Scattered showers across the Cape and islands. Today...Moderate Confidence. Mainly VFR conditions. May see brief local MVFR conditions in any scattered showers mainly across N Mass. Low risk for isold thunderstorm through midday. Conditions should improve from W-E through mid-late afternoon. Tonight...High Confidence. VFR. Thursday...Moderate confidence. Mainly VFR CIGS, though may see brief MVFR along the S coast in showers. May see brief heavy downpours around midday near and S of the Mass Pike with VSBYS locally MVFR to brief IFR. KBOS TAF...High confidence. VFR. Low risk for brief -TSRA around midday today. KBDL TAF...High confidence. VFR. Outlook /Thursday Night through Sunday/... Moderate to High confidence. Thursday night...Any low cigs/vsbys from Thursday will improve to VFR during the night. Areas of IFR in fog after midnight especially in the CT Valley and the normal fog spots. Friday through Sunday... VFR. Sea Breezes likely, especially Friday.
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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 Thursday/...High confidence. Today...W-SW winds will remain light with gusts 15 kt or less. Increasing S-SE swells will bring seas up to 5-6 ft across the southern waters and into RI and BI sounds. Have hoisted small crafts for this. Brief reduced vsbys in patchy fog through 12Z- 13Z, then in leftover showers across the Cape and islands through mid morning. Tonight and Thursday...Expect light SW winds to become SE on the southern waters during Thursday afternoon. Expect ocean swells to subside on BI and RI sounds by sunrise Thursday, but will linger a bit long over the open waters. They should subside during Thursday. Vsby restrictions in showers and patchy fog. Outlook /Thursday Night through Sunday/... Moderate confidence. Winds remain below 25 knots and seas below 5 feet through the period. The southern waters may experience a 4 foot swell Friday. Local sea breezes expected Friday, possible Saturday.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory for hazardous seas until 11 AM EDT Thursday for ANZ254>256. Small Craft Advisory for hazardous seas from 2 PM this afternoon to 5 AM EDT Thursday for ANZ235-237. && $$ SYNOPSIS...WTB/EVT NEAR TERM...EVT SHORT TERM...EVT LONG TERM...WTB AVIATION...WTB/EVT MARINE...WTB/EVT

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