Area Forecast Discussion
Issued by NWS Boston, MA

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151 FXUS61 KBOX 200521 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 121 AM EDT Sun Aug 20 2017 .SYNOPSIS... A cold front will cross region overnight, followed by very warm but less humid air on Sunday. High pressure brings dry and seasonable weather Monday. It will be hot and humid Tuesday. ahead of an approaching cold front, which will bring a chance of showers and thunderstorms from late Tuesday afternoon into early Wednesday afternoon. High pressure will bring dry and cooler weather late in the week into next weekend. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... 120 AM Update... Showers were dissipating over western MA where airmass is more stable and is a bit drier aloft than to our west. May still see brief shower or sprinkle across western/central MA into Merrimack valley through sunrise, otherwise dry weather is expected overnight. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/... Sunday... Spectacular late summer weather tomorrow with mid level mean trough axis pushing offshore resulting in height rises across the area. Warming temps aloft and flow becoming less cyclonic will yield less diurnal clouds/more sunshine than today. Model soundings show a deep boundary layer with drier air aloft mixing to the surface. This combined with downslope WNW winds will result in dew pts falling into the upper 50s. So despite temps climbing well into the MU80s to near 90, lowering dew pts will make it somewhat tolerable. Given the deep blyr and downsloping winds, increased temps a few degs warmer than guid. Sunday night... Any diurnal clouds erode with sunset giving way to mostly clear skies. This combined with high pres building into the area will promote radiational cooling and temps falling into the upper 50s outside of the urban areas. Used MOS temps to derive mins tomorrow night. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Big Picture... At upper levels, closed low pressure will be moving slowly across Canada, from west of James Bay Tuesday to eastern Quebec by Saturday. The trough axis extending southward from the low will remain to our west until Saturday. The cold pool of air will arrive over our region around Thursday and remain in place into next weekend. At the surface, high pressure will pass southeast of the region Monday. A cold front moves through Wednesday. Then strong high pressure builds over the Great Lakes states, with its influence extending eastward into New England. Details... Monday... High pressure off the DelMarVa coast will provide sunny skies for southern New England, warm temperatures, and relatively light southwest winds. Forecasting highs in the mid to upper 80s over most of the interior, with comfortable humidity. Tuesday... Southwest breezes behind departing high pressure and well in advance of an approaching cold front will usher in very warm and more humid air. With 925 mb temperatures of about 25C, am expecting highs to reach the upper 80s and lower 90s. Winds could gust to 15-20 mph during the afternoon. Dewpoints will be rising to near 70 by late afternoon and heat indices will be in 90-94 range, just shy of heat advisory criteria. With the afternoon heating will come a chance of a few showers and thunderstorms late in the day, especially in western MA and northern CT, closer to the approaching front. Tuesday night-Wednesday... A cold front will slowly work its way across the region. Showers and thunderstorm probabilities increase to 40-60 percent Tuesday night and mainly in eastern sections on Wednesday. The ECMWF is slower with the frontal progression than the GFS. Wind fields are somewhat strong, with 35-40 kts at 925 mb and 850 mb Tuesday night. Cannot rule out a few strong thunderstorms Tuesday night, even though they would not be occurring during the maximum heating. Skies will be clearing from west to east during the day. West to northwest winds could gust to 20 to 25 mph behind the front. Highs mainly 80 to 85 Wednesday. Thursday-Saturday... Strong high pressure building into the Great Lakes states will exert its influence across New England. At the same time, an upper level trough will be moving overhead, along with it associated cold pool with 500 mb temperatures reaching -18C Thursday and continuing into Saturday. It also will be cooler in the lower levels. Forecasting high temperatures in the 70s each day, possibly near 80 in spots. It should be dry for the most part, with scattered diurnal clouds. && .AVIATION /05Z SUNDAY THROUGH THURSDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/... 06z TAF Update...High confidence. LIFR in fog will persist around ACK through sunrise, before rapid improvement to VFR. Otherwise VFR today and tonight. Winds shift to W/NW and gust to 15-20kt at times from late morning into afternoon, especially across interior, before diminishing late in the day. VFR Monday with W/SW winds, gusting to 15-20kt near South Coast in the afternoon. Low chance of a sea breeze along East Coast for a few hours early in afternoon, but right now we are more confident in no sea breeze occurring. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Monday Night through Thursday/... Monday Night through Tuesday...High confidence. VFR. Only exception will be IFR in patchy late night fog, mainly Monday night, then improving to VFR by mid morning Tuesday. Tuesday night-Wednesday...Moderate confidence. VFR Tuesday but areas of MVFR cigs/vsbys in showers and thunderstorms late Tuesday afternoon in western sections, across the region Tuesday night and Wednesday morning, and in eastern sections Wednesday afternoon. IFR cigs possible in early morning fog/low clouds especially in areas that have had rain. Clearing in west half Wed. afternoon. Clear Wed night. Thursday... High confidence. VFR. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Monday/...Moderate confidence. Tonight... Onshore winds across the eastern MA waters veer to the SW after sunset and then west toward daybreak. Patchy low clouds/fog will also move offshore with the wind shift this evening and especially toward daybreak. Elsewhere, SSW winds continue with areas of fog possibly redeveloping along the south coast. Chance of a shower late tonight, especially along the north coast. Sunday... Modest WNW winds will promote dry weather and good vsby. Sunday night... WNW winds become very light as high pres build in from the west. Dry weather and good vsby prevail. Outlook /Monday Night through Thursday/... Monday through Tuesday...High confidence. High pressure south of the waters. Southwest winds remain less than 15 knots Monday but may increase to near 20 knots late Tuesday. Seas less than 3 ft, but increasing to 3 to 4 ft over the outer waters late Tuesday. Tuesday night-Wednesday...Moderate confidence. A cold front approaches from the Great Lakes, crossing the waters late Wednesday or Wednesday night. Southwest winds increase with gusts 20 to 25 knots during Wednesday. Winds shift to the northwest Wednesday night. Seas build Tuesday night and Wednesday reaching 5 to 6 ft on the outer waters. The southwest flow may also nudge those higher seas into RI Sound as well. A Small Craft Advisory may be needed on some of the waters during this time. Thursday... High confidence. As high pressure to our north and west builds over the northeast states, winds will turn more to the north and northeast. But they will be diminishing to less than 10-15 knots and seas will subside to 3 ft or less. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Nocera/GAF NEAR TERM...JWD SHORT TERM...Nocera LONG TERM...GAF AVIATION...JWD MARINE...Nocera/GAF

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