Area Forecast Discussion
Issued by NWS Boston, MA

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973 FXUS61 KBOX 200227 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 1027 PM EDT Thu Oct 19 2017 .SYNOPSIS... High pressure will maintain dry weather and warmer than normal temperatures through the weekend. The risk of showers will increase by the middle of next week. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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1020 PM update... Winds have diminished considerably over the interior but latest check with Steamship Authority shows 20-30 kt gusts continuing on Nantucket and Vineyard Sounds. Have increased winds in that area and prolonged them for a few additional hours overnight...hence have extended Small Craft Advisories for the southeast waters through 10Z.Lows will mainly be in the upper 30s and range from the upper 30s and 40s...which is about normal. Expect min temps in the 40s and low 50s. Temperatures and dewpoints right on track, so no changes made. Mid level trough will be racing across the northeast state overnight with a weak cold front causing a wind shift to the northwest. Mainly high clouds, but the NARRE, which performed well last night, is showing the development of a brief period of low cloudiness in the slopes of the Berkshires and into the CT River Valley toward daybreak. Will keep an eye on this. Some patchy fog cannot be ruled out in areas that have good radiational cooling overnight. Lows mainly in the 40s except lower 50s Cape Cod and Islands.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... High pressure remains in control with dry weather and mainly clear skies. Main difference from today will be that winds will be from the northwest and bringing slightly lower dew points. Mixing during the day will reach 925 mb or a little higher, similar to today, with temps at that level supporting max sfc temps of roughly 65-70F. At night, light wind with dew points 35-45 will allow radiational cooling to bring min sfc temps in the upper 30s and 40s. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Highlights... * Warm and dry this weekend lasting into Monday * Unsettled weather pattern with showers at times Tue into Thu Overview... Strong subtropical ridge along the east coast will maintain warm and dry conditions into early next week. Then models signal a pattern change with significant amplification of the large scale flow as northern stream trough digs south from the Great Lakes to the SE USA and interacts with southern stream energy with an eventual high amplitude trough setting up across the eastern seaboard. With downstream ridging shifting over the Atlantic, there could be a period of unsettled weather sometime in the Tue to Thu timeframe but timing and details remain uncertain in this developing complex pattern. Saturday through Monday... High pres in control with building mid level ridge will result sunshine and unseasonably warm weather. With 925 mb temps 17-18C should see highs reach well into the 70s this weekend but somewhat cooler along the south coast with SW flow. Warm and dry conditions last into Mon. Tuesday through Thursday... Unsettled with showers at times as amplifying trough sets up to the west with slow moving frontal boundary approaching and multiple shortwaves moving through the flow. Timing and details of rainfall remain uncertain but it appears there will be one period of rainfall sometime Tue into Tue night with lead southern stream shortwave lifting to the NE. Then possibly a break followed by another period of rain Thu and beyond as frontal boundary stalls with another system approaching. Very complex pattern so further forecast changes expected. Temps above normal through Wed, but lower confidence Thu. && .AVIATION /02Z FRIDAY THROUGH TUESDAY/...
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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 Friday Night/...Generally high confidence. Overnight... A weak cold front crosses the region tonight, but with very limited moisture, so just a few high clouds. The main effect will be a shift of diminishing winds with winds coming from the northwest overnight. Radiational cooling will allow patches of fog to develop later tonight, especially in parts of the CT River Valley and in the usual fog magnets. Vsbys could drop to 1/2 mile in spots after midnight. Could also see some low clouds/IFR ceilings developing in the slopes of the Berkshires and into the CT River Valley. Friday and Friday night... VFR conditions continue. Areas of fog will dissipate first thing Friday. Northwest winds will pick up a little, with late morning and afternoon gusts near 20 knots. Winds then diminish with sunset. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Will need to watch for a possible brief period of low clouds near the airport toward daybreak, though. Outlook /Saturday through Tuesday/... Through Monday...High confidence. VFR, but patchy late night fog possible in the typical locations. Tuesday...Moderate confidence. MVFR possible in developing showers.
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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 Friday Night/...High confidence. Overnight...Have extended the Small Craft Advisories for all waters, except Boston Harbor and Narragansett Bay through the overnight hours. Latest check from the Steamship Authority shows gusts of 20-30 kt continuing over Vineyard and Nantucket Sounds. Models show the gradient slowly weakening there toward daybreak. Seas on the outer waters will hover around 5 feet, and while the flow is from the southwest these 5 foot seas may work into RI Sound as well. Winds will shift to the northwest later tonight, at which point the seas will diminish. Friday...Northwest winds will gust around 20 knots during the day. Seas will remain 4 feet or less through the day. Friday night...Winds remain 15 knots or less, and seas remain at 3 feet or less. Outlook /Saturday through Tuesday/...High confidence. Great boating weather through Mon with SW winds below 20 kt and seas below SCA thresholds as high pressure prevails. Increasing southerly winds Tue as low level jet develops. High prob of SCA winds with low risk for gales. Increasing threat of showers with reduced vsbys Tue.
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&& .FIRE WEATHER...
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Winds shift to the northwest overnight. On Friday these northwest winds will gust around 20 mph, with minimum RH values reaching 30-35 percent across much of the region. Thus there could again be some risk of elevated fire weather potential. A Special Weather Statement highlights this potential.
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&& .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 6 AM EDT Friday for ANZ231>234-250- 251-254. Small Craft Advisory until midnight EDT tonight for ANZ230-236. Small Craft Advisory until 7 AM EDT Friday for ANZ235-237-255- 256.
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&& $$ SYNOPSIS...WTB/KJC NEAR TERM...WTB/KJC/GAF SHORT TERM...WTB LONG TERM...KJC AVIATION...WTB/KJC/GAF MARINE...WTB/KJC/GAF FIRE WEATHER...WTB/KJC/GAF

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