Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 211715 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 115 PM EDT SUN AUG 21 2016 .SYNOPSIS...
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Isolated showers possible this afternoon, but the vast majority of the day will be dry with increasing humidity. More widespread showers and thunderstorms with locally heavy rain will move through the region tonight with a cold front. A few strong thunderstorms are possible. Dry, cooler weather returns for Monday and Tuesday. They will be replaced by warmer and more humid weather Wed through Fri along with the risk of showers and thunderstorms by weeks end. Dry weather may return next weekend.
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&& .NEAR TERM /THROUGH TONIGHT/...
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115 PM Update...A few showers are in place across the Berkshires. Some of these are spilling over into southern New England. Don`t expect them to move much further east through the afternoon. These showers will bring very localized bits of rain, with most totals under a tenth of an inch. Widespread showers with perhaps some embedded thunder lies in front of the cold front through central NY state and into PA at this time. This will be our rain for the overnight period. It is quite slow moving at this time so feel our current timing is quite good. Otherwise, partly to mostly sunny conditions will continue through the afternoon with temperatures ranging from the 70s on the Cape and Islands through the upper 80s in the CT valley. Tonight...Low pressure moving through Quebec ahead of a shortwave will bring a cold front through southern New England. Ahead of this front, a line of showers and thunderstorms is expected to move across the region. Tropical moisture, drawn in on southerly winds, will bring in precipitable waters over 2 inches. This will result in periods of heavy rainfall with these showers and storms. While the storms and front are expected to move quickly across the area, such heavy rainfall may result in some urban and poor drainage street flooding, especially in typical areas. The best chance for heavy rainfall will be across western MA and northern CT where the jet is stronger. In addition, surface based and mixed layer CAPEs are about 500 J/kg and 0-6km shear values between 40 and 50 kts, is enough for a risk of strong storms. This is not a setup that usually produces much severe weather, but the risk for some isolated wind damage is there. The models are not developing a secondary low pressure system over southern New England as strongly as they were overnight and yesterday. That said, should one develop, there is a very low probability of a brief tornado or waterspout developing. However, this is a very low probability.
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&& .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/...
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Monday...Most, if not all, of the overnight precip should be offshore by Monday morning. If anything, expect perhaps a few showers lingering on the Cape and Islands. As the cold front moves offshore during the morning, gusty NW winds will increase. A decent low level jet, good mixing, and a tight pressure gradient between the low exiting to the maritimes and the high building over the OH valley will be responsible for these gusty winds. In addition, a marked decrease in dewpoints and relative humidities as well as temperatures a few degrees cooler will result in a cooler feeling day. High temperatures expected to be in the upper 70s to lower 80s for most locations with a few cooler readings across NW MA. Monday night...High pressure builds more over southern New England. This will result in light winds and clear skies and excellent radiational cooling conditions. With dewpoints in the upper 40s to lower 50s for much of the area, expect low temperatures to be quite brisk and fall like Monday night.
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&& .LONG TERM /TUESDAY THROUGH SUNDAY/...
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Highlights... * A touch of fall-like temps Tue * Warmer and more humid Wed thru Fri * Dry much of next week except a risk of T-storms Fri Overview and model preferences ... The subtropical ridge over the southeast states re-emerges and builds northward along the eastern seaboard Wed thru Fri. This will result in a return to warmer and more humid weather for southern New England. By the end of the week both ensembles /GEFS and EPS/ and deterministic guidance in good agreement that next northern stream short wave trough will exit the northern plains into the Great Lakes and then thru the St. Lawrence River Valley. This feature will lower heights across New England and open the door for a surface cold front to traverse the region. Good agreement among all guid sources that heights continue to lower across New England into Sat...driving frontal boundary offshore and promoting high pres over the Great Lakes to build into New England. Thus at least avg forecast confidence on a trend toward drier...not as warm and less humid weather next weekend. Details ... Tuesday ... 1026 mb high advects over the region resulting in a weak pgrad and promoting afternoon seabreezes. Despite weak cyclonic flow aloft column is dry and will support mostly sunny conditions. Cool start to the day combined with limited blyr mixing given 1026 mb high overhead will cap highs mainly 75 to 80. Very comfortable with dew pts remaining in the 40s. Wed/Thu and Fri ... Subtropical ridge builds back up the Eastern Seaboard this period yielding a return to a warmer and more humid regime. Highs climbing back to 85 to 90 Thu and Fri away from the south coast. Dew pts also climbing thru the 60s to possible 70. Northern stream short wave and attending cold front Fri will result in a risk of T-storms. Saturday ... Good agreement among ensembles and deterministic guid that height falls continue over New England...eroding the subtropical ridge and pushing the frontal boundary offshore. This suggest a trend toward drier...not as warm and less humid weather. However it`s day7 so won`t get too deep into the details just yet.
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&& .AVIATION /17Z SUNDAY THROUGH THURSDAY/...
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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 Monday Night/... Through 00Z...High confidence. Mainly VFR conditions. Exception will be the CT valley where MVFR conditions are possible at times through the afternoon. Isolated SHRA possible this afternoon, mainly across W MA/N CT. Tonight...High confidence in trends...moderate confidence in timing. VFR conditions deteriorate to MVFR between 00-03Z in the west and 03- 06Z in the east as widespread SHRA/isolated TSRA move in from the west. Periods of heavy rainfall are likely with these showers and storms, resulting in IFR conditions. Conditions improve to VFR in the west beginning about 09Z and possibly in the east as early as 12Z. Monday and Monday night...High confidence. Any locations not VFR will improve to VFR quickly Monday morning. VFR conditions will continue through the period. Gusty NW winds are likely Monday. KBOS Terminal...Moderate to high confidence in TAF. Main risk for heavy showers and embedded thunderstorms between 05Z and 09Z. KBDL Terminal...High confidence in TAF. Main risk for heavy showers and embedded thunderstorms between 01Z and 05Z. Outlook /Tuesday through Friday/... High confidence in a stretch of mainly dry VFR weather. Sea breezes most likely mid-late week.
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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 Monday Night/...High confidence. Quiet boating weather is expected through the period, with a slight rise in winds and seas ahead of a cold front tonight. Otherwise, a chance of showers and thunderstorms tonight will be the main hazard to boaters. Keep an eye on the weather tonight and remember that lightning and gusty winds are always a possibility in any thunderstorm. Quiet weather returns for Monday, though gusty NW winds may reach close to SCA criteria during the afternoon. Outlook /Tuesday through Friday/...Moderate confidence. Tuesday through Thursday ... High confidence. Quiet boating weather as slow moving high pressure builds over the waters. By Thu SSW winds will likely become gusty near shore.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Nocera/RLG NEAR TERM...RLG SHORT TERM...RLG LONG TERM...Nocera AVIATION...Nocera/RLG MARINE...Nocera/RLG

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