Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 300735 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 335 AM EDT TUE AUG 30 2016 .SYNOPSIS... High pressure over New England will move offshore by tonight. Warm and humid weather returns Wednesday. A cold front moves through Wednesday night and Thursday, which will bring scattered showers and a few thunderstorms. Large high pressure will build out of central Canada, bringing dry, seasonable conditions into the upcoming holiday weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... High pressure over the Northeast USA will mean lots of sun today along with light wind. Mixing profiles suggest a layer up to 850 mb, where temps will be 13-14C. That supports high temps in the low to mid 80s. The light flow will allow sea breezes to develop, which will keep high temps a little cooler along the coast. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
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Tonight... High pressure moves offshore, bringing a slow increase in surface flow from the west-southwest. This suggests increasing dew points, which will hold temperatures a little milder than tonight. The light flow will also allow areas of fog to develop. We are using the dew point range to forecast min temps, in the upper 50s and 60s. Wednesday... Upper shortwave dives southeast from central Canada, driving a cold front over the Eastern Great Lakes. This shortwave will also move a 90-knot jet south through New England. The ECMWF shows this more than the GFS. The ECMWF is also less distinct with dynamically favored locations along the jet, while the GFS is more distinct and shows favorable dynamics across Northern New England. Moisture fields are rather thin most of the day, increasing a little during late afternoon. CAPEs climb to around 500 J/Kg and Totals to the upper 40s. Much of this is concentrated over Western MA. We also should consider the ongoing drought, which works against confidence for measurable precip. We will continue with low-end chance pops late-day in Western and North-central MA, and slight chance across Nrn CT and the remainder of Northern MA. Temps at 850 mb climb to 16-17C, suggesting max temps in the mid to upper 80s.
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&& .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
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HIGHLIGHTS... * Cold front brings showers and thunderstorms Wed night into Thu * Dry weather and seasonable temps through much of the holiday weekend * Rough surf and rip currents could occur mid to late week due to SE swells from distant Hurricane Gaston While the 00Z model guidance is in overall good agreement on the general synoptic pattern throughout the long term portion of the forecast, there are a few complicating factors. Namely, Tropical Depression Eight and Tropical Depression Nine, and to a lesser extent Hurricane Gaston. TD 8 is off the Carolina coastline currently and is expected to become a tropical storm sometime later today and pass well to the SE of southern New England. While it is something to keep an eye on, the only impacts to southern New England are expected to be on the waters. TD 9 is in the Gulf of Mexico currently and is forecast to move through the eastern part of the Gulf before crossing northern Florida back into the Atlantic late in the week. This is the main potential complicating factor. At this point, the ensemble runs of both the ECMWF and the GFS build an upper ridge/high pressure well into southern New England through early next week, keeping TD 9 well south of the area. This lines up well with previous forecasts including the National Hurricane Center`s forecast. However, the 00Z operational GFS run keeps the upper ridge a bit farther west and weakens the high pressure allowing it to move eastward away from the east coast. This would allow TD 9 to make a much closer approach to southern New England. While this solution is an outlier currently, we will need to keep an eye on future guidance trends. Finally, Hurricane Gaston is hanging out in the middle of the Atlantic and is forecast to stay well out to sea. However, it will push higher swells into the southern New England coastline, resulting in rough surf, rip currents, and choppy seas just in time for the holiday weekend. Overall, the weather will be fairly quiet through the long term. The main exception to this will be Wednesday night into Thursday when low pressure in Quebec will bring a cold front through southern New England. This may result in scattered showers and a few thunderstorms. While ingredients are there for this to occur, given the trends in the region towards drought, have less confidence in the much higher PoPs given in the models. Therefore, have lowered PoPs to low end chance, but kept the possibility of a few scattered showers and storms. Definitely won`t be a washout, but a few areas may see some much needed rain. Otherwise, until we see what the tropics end up doing, expecting seasonable temperatures and dry weather through the end of the week and warming temperatures through the weekend.
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&& .AVIATION /08Z TUESDAY THROUGH SATURDAY/...
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Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Through Wednesday...High confidence. Mainly VFR outside of a few patches of fog early this morning and again early Wednesday morning at typically prone locations. Light variable winds today will give way to sea breezes on all coasts. Winds then pick up a little from the west-southwest Wednesday. KBOS Terminal...High confidence in TAF. A NE-SE sea Breeze develops starting around 14z. KBDL Terminal...High confidence in TAF. Outlook /Wednesday Night through Saturday/... Wednesday night and Thursday...High confidence. Mainly VFR conditions. Low probability of SCT -SHRA/ISOLD TSRA, resulting in brief MVFR conditions. Friday and Saturday...High confidence. VFR.
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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 Wednesday/...High confidence. Today... North to northeast winds become variable. Sea breezes will develop late morning and afternoon. Continued swell from Tropical Storm Gaston and Tropical Depression 8 will continue to bring 5 foot seas to the outer coastal waters. Tonight and Wednesday... With high pressure departing, winds will pick up from the southwest but remain below 20 knots. Swell from the tropical systems will diminish on the Southern Outer Waters but increase on the Eastern Waters, near the Gulf of Maine. Small craft advisories will move as this focus moves east. Outlook /Wednesday Night through Saturday/... Wednesday night and Thursday...High confidence. Winds and seas remain below SCA criteria for the most part. There is a possibility of a few 5 foot seas on the outer waters. There is also a low probability of a few scattered showers and thunderstorms over the waters. Friday and Saturday...Moderate confidence. Winds and seas expected to remain below SCA criteria. However, SE swell starts to increase in response to distant Hurricane Gaston. This may result in rough surf and an increase in rip currents.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 4 PM EDT Wednesday for ANZ250-254. Small Craft Advisory until 6 AM EDT Wednesday for ANZ255-256.
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&& $$ SYNOPSIS...WTB/RLG NEAR TERM...WTB SHORT TERM...WTB LONG TERM...RLG AVIATION...WTB/RLG MARINE...WTB/RLG

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