Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 200549 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 149 AM EDT Fri Oct 20 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 THIS MORNING/...
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145 AM update... Thick cirrus was overhead as an upper level shortwave trough moves across the region. Winds were still out of the southwest, as the surface trough has not moved completely through. Expecting a shift to the west, then northwest over the next few hours. Winds had diminished over the interior but were still gusting to 20-25 mph over Cape Cod and the islands. The cloud cover was holding temperatures a little higher than forecast...still in the 50s in most areas. But as skies slowly clear, temperatures should drop to the 40s to lower 50s most areas.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SATURDAY/... 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 NIGHT 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 /06Z 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 Saturday/...Generally high confidence. 145 AM update... Overnight...Overcast high cloudiness across the region Radiational cooling may allow patches of fog to develop later tonight in parts of the CT River Valley. Could also see some patchy low clouds/IFR ceilings developing in the slopes of the Berkshires and into the CT River Valley toward daybreak. Later today and tonight... VFR conditions continue. Any fog will dissipate first thing after sunrise. 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 Night 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 Saturday/...High confidence. 145 AM update... Overnight...Small Craft Advisories continue for all waters, except Boston Harbor and Narragansett Bay through the overnight hours. Winds were still gusting to 20-25 kt 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 Night 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... 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. && .BOX WATCHES/WARNINGS/ADVISORIES...
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CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 6 AM EDT early this morning for ANZ231>234-250-251-254. Small Craft Advisory until 7 AM EDT this morning 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

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