Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 131140 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 740 AM EDT Sun Aug 13 2017 .SYNOPSIS...
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High pressure brings dry weather today and Monday. A cold front will bring the chance for showers and thunderstorms Tuesday afternoon, pushing offshore Tuesday night. Large high pressure builds as another dry front moves across during the mid week. A warm front approaches Thursday night and Friday, bringing scattered showers along with the threat for thunderstorms on Friday. Showers may linger into Saturday as low pressure approaches.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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730 AM Update... Low clouds and fog are quickly breaking with the rising sun. Noting thinning clouds especially away from the coast on latest GOES-16 5 min visible imagery. More clouds are lingering across RI/E Mass and across the Berkshires, with some clouds across central and W Mass into NE CT mainly lower clouds in the river valleys. Observations at the airports, except along the S coast, have shown fast improvement over the last hour or so. Expect lower, thick clouds to continue to push offshore this morning as the cold front, depicted across the CT valley at 11Z, will continue to shift slowly E through this afternoon. Temps at 11Z ranged from the lower-mid 60s across the valleys of N central and NW Mass to the lower 70s across E coastal areas to SE Mass and RI. Once the clouds have cleared out, expect readings to quickly recover to the 70s to lower 80s by midday, mildest across the coastal plain. Have updated near term forecast to bring conditions current and incorporate into the morning forecast trends. Previous Discussion... Low level dry air will start to envelop our region later this morning. This should bring showers to an end around daybreak. This drier air and a fairly deep mixed layer should also help to bring an end to the humid conditions. Typically, MOS guidance in our region is too high when winds are west to northwest. Will lower dewpoints later this afternoon to account for this bias. Plenty of sunshine for most of today, so max temperatures should be near normal.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... HIgh pressure builds into our region tonight into Monday. Dry weather prevails with lower humidity. Some patchy fog may develop in the typical low lying regions tonight, but will not be widespread. Near normal temperatures through this period. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/...
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Overview... Continued long wave trough across the eastern third of the U.S. extending from H5 vortex spinning near or just E of Hudson Bay at the start of the long term period. Noting a potent short wave moving across the Great Lakes, pushing toward the region from mid-late afternoon Tuesday into Tuesday night. Mainly a positively tilted trough along with general W-NW mid level flow so should push through rather quickly. Long wave ridging builds out of the northern Plains by mid week, which tends to flatten out as a progressive steering flow takes over across the northern tier into late next week. Some question on timing of next short wave in the mid level steering northern stream flow as H5 cutoff low across of Manitoba and Saskatchewan may push a short wave toward the region by next weekend. Timing and track issues in place with this system. Surface frontal system may try to push eastward around the Fri- Sat timeframe with another shot for showers and/or thunderstorms. Details... Monday Night...High confidence. High pressure pushes offshore, but will remain dry during this timeframe. Patchy late night/early morning fog develops especially in normally susceptible interior valleys as well as along the coast. Tuesday...Moderate confidence. Potent short wave approaches from the W. Scattered showers develop Tuesday afternoon/evening across the interior. Strong low level lapse rates, along with low level moisture. Also noting LIs around zero to -1. PWATs not terribly high, at about 1.25 inches. Still mixed signals as mentioned by previous forecaster, but SPC has mentioned a marginal risk for strong to severe storms during this timeframe. Mentioned chance POPs mainly from N central and W Mass into N central CT. Expect precip to dissipate with sunset. Wednesday and Thursday...Moderate confidence. A dry cold front pushes southward across the region as high pressure builds across from Quebec. Temps on Wed will be in the lower-mid 80s, except a bit cooler along the shore and higher terrain. Readings will fall back a few degrees on Thursday as H5 heights drop a bit after the frontal passage. Clouds will increase from W-E during Thursday afternoon, along with scattered showers pushing into western areas. Thursday night through Saturday...Low to moderate confidence. Warm front starts to approach Thursday night, bringing increasing deep low level moisture field. PWATs increase to 1.8 to 2 inches. S-SE winds in place will begin to increase as well, especially along E coastal locations, which will become generally SE by Friday. May see wind gusts up to 15-20 kt along the east coast. Best shot for precip looks to move across central and northern areas, but will be dependent upon track of the low pressure. Lower confidence due to model solution disparity, with the ECMWF a fast outlier. Should see best chance for showers Thu night into Fri, with low instability working into southern areas with the threat for isolated thunderstorms. GFS and GGEM continue to hold moisture across the region Fri night into Sat with onshore winds.
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&& .AVIATION /12Z 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/... Today...High confidence. MVFR-IFR conditions across the interior river valleys and across coastal areas will improve to VFR by mid to late morning. W-SW winds will shift to mainly W by late morning, with gusts up to 20 kt mainly along the coast. Tonight...High confidence. Mainly VFR. Patchy MVFR fog possible in low lying terminals. Monday...High confidence. VFR. Seabreeze along the coasts from mid morning through the afternoon. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Monday Night through Thursday/...Moderate confidence. VFR conditions through most of the period. May see areas of MVFR-IFR CIGS/VSBYS in late night/early morning fog each night. Brief MVFR CIGS/VSBYS across the interior Tuesday afternoon/evening. Scattered showers with local MVFR conditions from W-E during Thursday.
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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/...High confidence. Southerly flow will continue to strengthen ahead of an approaching cold front. A few gusts near 20 kts are possible. This will help increase seas to near 5 feet today into this evening across the southern waters. High pressure building late in the day, and especially tonight, will help seas subside below 5 ft. Outlook /Monday Night through Thursday/...Moderate confidence. Winds and seas should remain below small craft criteria through Thursday. May see south wind gusts to 20 kt on the eastern waters Tuesday. Seas below 4 ft through the period. Low pressure passes well offshore but may bring light showers across the southern outer waters Tuesday. Visibility restrictions in patchy fog late Monday night into Tuesday across most waters, then in scattered showers Tue. Return of patchy late night/early morning fog across most waters Tue and Wed nights. Scattered showers may push across the waters on Thu with more local visibility restrictions.
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&& .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EDT Monday for ANZ254-255. Small Craft Advisory until 8 PM EDT this evening for ANZ235- 237. Small Craft Advisory until 11 PM EDT this evening for ANZ256. && $$ SYNOPSIS...Belk/EVT NEAR TERM...Belk/EVT SHORT TERM...Belk LONG TERM...EVT AVIATION...Belk/EVT MARINE...Belk/EVT

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