Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 261139 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 739 AM EDT TUE JUL 26 2016 .SYNOPSIS... High pressure will bring dry but continued hot conditions today and Wednesday. A cold front will slowly push into the region during Thursday, then looks like will linger through this weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 730 AM Update... Mainly clear skies across the region early this morning, except for some wispy cirrus clouds in a few spots at 11Z. Noting W-SW winds in place across most of the region at 10 KT or less, with calm winds in valley locations. Expect winds to shift to W-NW during the morning/midday hours as mid level short wave shifts E. Temps already recovering to the 70s to around 80 at most locations, which was close to previous forecast. Have updated near term to bring conditions current. Previous discussion... High pressure builds in from the west bringing subsidence and sunshine and deep mixing. But lingering moisture near 850 mb should allow for some diurnal clouds to develop. Mixing will bring down some wind gusts near 20 knots. Temps aloft are roughly 15C-17C on the GFS and 16C-18C on the ECMWF. Mixing should allow for max surface temps in the upper 80s to mid 90s. Dew points over Upstate New York are in the mid 60s, with low 60s to the north and west. This will mean a little less humidity, but still enough to be noticed. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/... Tonight... High pressure builds in with diminishing wind. Dew points 60 to 65 will keep min temps in the 60s, with low 70s along the coast. Wednesday... High pressure remains in control with sunshine. Upper flow shows a weak shortwave moving through, but less cloud-level moisture for sky cover. Light wind near the surface will allow for developing sea breezes along the coasts. Temps aloft around 18C should support sfc max temps in the interior in the low to mid 90s, cooler values near the coastline. Dew points linger around 60 or in the lower 60s. && .LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/... Highlights... * Cold front approaches the region during Thursday * Showers and isolated thunderstorms remain possible Friday into the weekend Overview and model preferences... 00Z model suite remains in pretty good agreement through Thursday, then continue to show wide model spread from Thursday night onward. This appears to be dependent upon development of short waves in the nearly zonal H5 flow across the northeast, which will start to back to SW as broad mid level troughing develops across the Great Lakes into the weekend. The big differences come into play as models handling the slow movement of the front out of northern New England differently, along with any low pressure waves that move along it. One thing that is in somewhat good agreement is that the front should push into the region around Friday, then will stall in the W-SW mid level flow through most if not all weekend. Used a blend of available guidance through Thursday, then went with mainly ensemble approach beyond that. Details... Wednesday night...Will remain dry and muggy conditions. Patchy late night/early morning fog develops mainly along the coast and some of the interior valleys, especially interior E Mass. Overnight lows in the lower-mid 60s well inland, ranging to around 70 along the coast and urban centers. Thursday...Models begin their solution variance during this timeframe, but in fair agreement. Will see another hot and humid day, especially along the south coast. Timing of slow moving front remains in question, but does appear scattered showers/isold thunderstorms may push into N central and W Mass into N central CT during the afternoon/evening hours ahead of the front. Have carried low chance POPs there, with isold showers possible further S and E. Kept isold convection going, can not rule out entirely with marginal instability in place. Decent H85-H5 lapse rates of 6-6.5C/km, with best shot during max heating of the day. Expect highs in the lower-mid 90s away from the coast, warmest across the CT valley, ranging to the upper 70s-mid 80s near the coast possibly touching 90 in Boston and on the north shore. Thursday night and Friday...Model solutions continue to widen during this timeframe with the movement, or lack thereof, of the front out of S VT/NH. Also questions on development of low pressure along this front, with the GFS being most robust. Have kept chance POPs going, as models do generally bring in scattered showers, and kept isold thunder as well. With more clouds around, will see high temps on Friday 5-10 degrees cooler than Thursday, mainly in the 80s. Saturday and Sunday...High uncertainty remains during this portion of the forecast, with a continued low confidence forecast. Both the ECMWF and Canadian GGEM models move low pressure off the mid Atlantic coast during Saturday, with precip working into the region, while the GFS remains the outlier. More questions on timing of short wave in the H5 flow on Sunday, so kept low chance POPs going there as well. Monday...Low confidence continues. Do have low chance POPs going inland into the afternoon, then have trended drier. Expect temperatures to run close to seasonal normals. && .AVIATION /12Z TUESDAY THROUGH SATURDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence. Today...VFR. W-NW winds with gusts 15-20 knots during the afternoon. Tonight...VFR. Patches of IFR cigs/vsbys in fog late at night. Wednesday...VFR. Fog burns off around sunrise. Light variable wind becoming onshore along the coastline. KBOS TAF...High confidence in TAF. KBDL TAF...High confidence in TAF. Outlook /Wednesday Night through Saturday/... High confidence Wednesday night. Moderate confidence Thursday through Saturday. Wednesday night...Mainly VFR conditions. Patchy fog possible after 07Z-08Z through 12Z along the immediate south coast, Cape Cod and the islands. Thursday through Saturday...Mainly VFR, except MVFR CIGS/VSBYS possible in scattered showers and thunderstorms. Potential for local MVFR-IFR in patchy fog and low CIGS each night. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Wednesday/...High confidence. Winds remain below 20 knots and seas below 5 feet through the period. Winds become Northwest today, then variable tonight and Wednesday. Outlook /Wednesday Night through Saturday/...Moderate to high confidence. Wednesday-Thursday...Winds and seas below small craft criteria. Patchy late night/early morning fog with reduced visibilities. Isolated showers/thunderstorms possible late Thursday/Thursday night. Friday-Saturday...Winds shift to S-SE but remain below small craft levels. Swells will build to around 5 ft on the southern outer waters Friday night into Saturday, then should subside. Patchy fog and scattered showers/thunderstorms will reduce visibilities. && .FIRE WEATHER... Much drier conditions are expected today across southern New England behind the departing cool front. Minimum relative humidity is expected to range from 30 to 40 percent across much of the area. The exception is along Cape Ann and the Cape/Islands, where minimum RH values of 40 to 60 percent are forecast. Northwest winds around 10 mph may gust to 20 mph at times. Winds are expected to be lighter on Wednesday with nearshore sea breeze development. However, minimum RH will again reach 30 to 40 percent across the interior. Along east coastal MA and southern RI, sea breezes will allow for higher minimum RH of 40 to 70 percent. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/EVT NEAR TERM...WTB/EVT SHORT TERM...WTB LONG TERM...EVT AVIATION...WTB/EVT MARINE...WTB/EVT FIRE WEATHER...WTB

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