Area Forecast Discussion
Issued by NWS Boston, MA

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601 FXUS61 KBOX 201852 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 252 PM EDT Fri Oct 20 2017 .SYNOPSIS...
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High pressure will move from the Appalachians today to a position east of New England on Sunday. The high will bring warm dry weather for Sunday and Monday. A cold front brings showers Tuesday and Wednesday. Cooler drier weather returns late in the week.
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&& .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... 2 PM update... Not much change from previous forecast. Absolutely gorgeous weather taking place across southern New England at 130 pm with temps 65-70, dew pts in the 30s to lower 40s, a modest NW wind 10-20 mph and full sunshine. Enjoy! Earlier discussion below. ================================================================ SPS mesoanalysis indicates mean mid level trough axis east of New England and with upstream mean ridge axis across the Great Lakes. This will provide deep layer anticyclonic flow and associated subsidence into New England today. The 12z observed sounding from ALY reveals this well underway with a sharp mid level subsidence inversion just below 700 mb. This will provide the region with abundant sunshine and mild temps with highs 65-70, still warmer than normal. Northwest winds 10-20 mph will provide some downslope into the coastal plain, drying out the blyr with dew pts in the 30s mixing down to the surface from aloft. Overall, ideal weather for late Oct and certainly a top 10 day. Previous discussion below. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... 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 /SUNDAY THROUGH FRIDAY/...
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Big Picture... Ridge over the Eastern USA early in the week with above normal 500- mb heights foretells a mild dry start to the week. High amplitude trough digs over the Central USA during this time with a closed low forming over the Great Lakes by Tuesday. The low then sweeps east across New England Thursday-Friday. As the upper low approaches and then moves overhead, 500-mb heights over us will lower substantially, from the 580s to the 550s, which suggests much cooler temperatures later in the week. Mass fields begin to diverge Tuesday as the upper low formation takes off to our west-southwest. Thermal fields are similar through Wednesday then diverge. High confidence in forecast Sunday and Monday...confidence then diminishes through moderate the rest of the week. Details... Sunday-Monday... High pressure to our east with a light southerly flow across Southern New England. The period will be subsident with warm tempertures aloft. Main question will be the depth of the mixed layer with shallow mixing promoting cooler temps. Mixing to 900 mb would tap a 10C equivalent, while 925 mb would tap an 8-9C equivalent. Expect max temps in the 70s, possibly 80 if the mixing goes deeper. Dew points in the 50s suggests min temps mainly in the 50s. Tuesday-Wednesday... The digging upper trough, associated surface cold front, increased southerly flow ahead of the front, and increased moisture in that flow all point to a chance of showers Tuesday and Tuesday night with lingering showers Wednesday. Precipitable water values climb to 1.5 inches Tuesday and may reach 2.0 inches just ahead of the cold front Tuesday night. Totals are forecast to reach upper 40s and LI values marginally sub-zero, so thunder is not out of the question, especially just ahead of the front. Thursday-Friday... Upper trough moves across on Thursday. High pressure builds on Friday. Could be some leftover showers Thursday especially in Eastern Mass. Dry weather Friday.
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&& .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/...
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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 Night/...Generally high confidence. 2 PM update... High pressure provides VFR, dry weather and light winds tonight, Sat and Sat night. KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF. Outlook /Sunday through Wednesday/... Sunday...VFR. Sunday Night: VFR with local IFR in fog. Monday: VFR. Monday Night: VFR, with local IFR possible in fog. Chance SHRA late. Tuesday: MVFR, with local IFR possible. Breezy. Likely SHRA. Tuesday Night: MVFR, with local IFR possible. Breezy. Likely SHRA. Wednesday: Breezy. Chance SHRA.
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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 Night/...High confidence. 2 PM update... Very tranquil boating weather for late Oct with NW winds 10-20 kt, highest near shore. Good vsby and dry weather. Enjoy! Earlier discussion below. ================================================================ 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 /Sunday through Wednesday/...High confidence. Sunday through Sunday Night: Winds less than 25 kt. Monday: Winds less than 25 kt. Seas locally approaching 5 ft. Monday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers. Tuesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Chance of rain showers. Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 11 ft. rain showers Likely. Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 12 ft. rain showers Likely.
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&& .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...None. && $$ SYNOPSIS...WTB/GAF NEAR TERM...Nocera SHORT TERM...GAF LONG TERM...WTB AVIATION...WTB/Nocera MARINE...WTB/GAF FIRE WEATHER... CLIMATE...

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