Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 200715 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 315 AM EDT Fri Oct 20 2017 .SYNOPSIS... High pressure will move from the Appalachians today to a position east of New England on Sunday. It will provide dry and much warmer than normal temperatures through the weekend. The risk of showers will increase by the middle of next week. && .NEAR TERM /THROUGH TODAY/... 3 AM update... Satellite imagery shows that the upper level trough axis has shifted east of the region. A band of thick cirrus clouds over southern New England was beginning to pull out to the east. It should be mainly off the coast by daybreak, leaving mostly sunny skies across our area. At the surface, a weak, dry cold front will move through as a wind shift, with winds shifting to west toward daybreak and then to the northwest during the day today. Wind gusts to 20 mph are expected for a time late this morning and into the mid afternoon hours. Mixing during the day will reach 925 mb or a little higher, similar to yesterday, with temperatures at that level supporting max sfc temps around 70, except mid 60s in the slopes of the Berkshires and on Nantucket. && .SHORT TERM /TONIGHT THROUGH 6 PM SATURDAY/... Tonight... Skies will be clear and winds will be light. It will be on the chilly side with lows in the upper 30s to mid 40s, except mid 40s to lower 50s Cape Cod and the islands. Saturday... * Very warm weather, but may fall short of record highs High pressure will become centered just south of southern New England. An upper level ridge along the east coast will build into the region. 925 mb temperatures will reach +17C during the afternoon. With full sunshine, am expecting highs in the mid to upper 70s, but cannot rule out a high near 80 in Hartford County. Should be cooler...in the 60s to lower 70s...along the south coast, Cape Cod, and the islands with southwest flow. Record highs are 80 at Worcester, 81 at Providence, and 82 at Hartford and Boston...all set back in 1920. && .LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/... Highlights... * Warm and dry weather 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. Sunday through Monday... High pres still 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 Sunday 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 /07Z FRIDAY THROUGH TUESDAY/... 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. 3 AM update... Any isolated fog patches, especially in the CT River Valley, will dissipate first thing after sunrise. Otherwise VFR conditions through Saturday. Just an isolated fog patch or two late tonight in the normally colder spots. Northwest winds will pick up a little, with late morning and afternoon gusts near 20 knots today. Winds then diminish with sunset and will be light through Saturday. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. 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. && .MARINE... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday/...High confidence. 3 AM update... Today...Northwest winds will gust to around 20 knots during the day. Seas will be near 5 ft early this morning on the southern outer waters but seas will subside to 3 to 4 ft throughout all outer waters during the day. Have kept a Small Craft Advisory posted for the southern outer waters through 10 AM this morning. Tonight and Saturday...Ideal boating weather. Winds remain 15 knots or less, and seas mainly 2 ft or less. Wind direction will shift from the north tonight to the southwest on Saturday. 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. && .FIRE WEATHER... Will reissue the Special Weather Statement highlighting a risk of only marginally elevated fire weather potential for today. Northwest winds may gust up to 20 mph at times late this morning through the mid-afternoon hours. We are not expecting 25 mph or higher gusts. Minimum RH values will reach 30-35 percent across much of the region. These values, combined with the lack of recent rainfall will lead to a marginally elevated fire weather potential for today. && .CLIMATE... Record high temperatures for Saturday, October 21: BOS 82 in 1920 BDL 82 in 1920 PVD 81 in 1920 ORH 80 in 1920 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 AM EDT this morning for ANZ255- 256. && $$ SYNOPSIS...Field/KJC NEAR TERM...Field SHORT TERM...Field LONG TERM...KJC AVIATION...Field/KJC MARINE...Field/KJC FIRE WEATHER...Field CLIMATE...Field

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