Area Forecast Discussion
Issued by NWS Boston, MA

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119 FXUS61 KBOX 261856 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 256 PM EDT FRI AUG 26 2016 .SYNOPSIS... A cold front moves off the New England coast this evening. High pressure then builds over Northern New England, bringing dry weather for much of the weekend. As we go Sunday into Monday there is the chance of showers and thunderstorms ahead of a sweeping cold front. A brief period of high pressure follows for Tuesday prior to another cold front for Wednesday with again the chance of wet-weather. Low confidence forecast from Thursday onward as competing airmasses present the double-sided possibility of either wet- weather or remaining completely dry. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Through this evening... A cold front is moving through our area with scattered showers found south and east of a Boston-Hartford line. CAPE on the southern/warm side of the front reached 1500-2000 J/Kg. Other stability parameters are more marginal. This suggests a limited potential for thunder in RI and SE Mass until the front moves through. Tonight... Cold front should move offshore by midnight. Dew points are in the 70s ahead of the front and mid 60s behind, so expect the air to become a little more comfortable. Clearing skies already in Western MA will spread across all of Southern New England early tonight. Also expect winds to become light in the interior. Clear skies and light winds and dew points in the mid 60s should allow min temps to reach the mid and upper 60s most places, and low 70s Cape/Islands and urban spots. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... High pressure builds over New England with center along the Canadian border. This will bring a light wind inland and sea breezes along the coast. Dew points will continue to lower with readings near 60. Temps at 850 mb will be in the mid teens, so max sfc temps should reach the mid to upper 80s, with coolest temps along the coastline. The center of high pressure shifts east a little Saturday night, but fair skies and light winds remain in place over Southern New England through the night. With light wind and dew points lingering near 60, expect min temps roughly 60 to 65. && .LONG TERM /SUNDAY THROUGH FRIDAY/... */ Highlights... - Shower and Thunderstorm chances Sunday into Monday - Keeping it dry for Tuesday - Another cold front and chances of wet-weather for Wednesday - Low confidence forecast from Thursday onward - Keeping Invest-99L out of the picture and out to sea */ Discussion... Interpreting the N Hemispheric pattern. Atmospheric teleconnections continuing a -WPO/-EPO trend through the beginning of September with a waffling PNA. Of certainty, we`re seeing a buckling in the height pattern across the N Pacific in concert with a -WPO/-EPO yielding a high latitude block and stronger than normal Pacific jet within the deepening troughs. Given the PNA trend, there is no clear signal as to outcomes downstream. Nevertheless, during -EPO/-WPO trends it is noted that anomalous cyclonic circulations can occur over E portions of N America, drawing cooler air S. So while the late-August early- September cyclone in vicinity of the NE CONUS per deterministic guidance may seem erroneous, it can not entirely be rule out. Will for the sake of simplicity keep with an ensemble-weighted forecast. Inclined to believe per ensemble members and deterministic forecasts that at this point whatever becomes of Invest-99L (AL99) will sweep out N/E ahead of preferred troughing prior to and during the Labor Day Holiday Weekend. So will lean with the following forecast: Sunday into Monday a deamplifying disturbance which will introduce lower heights and cyclonic flow, a slight kink to the near-zonal flow. Surface cold- frontal feature, there is the chance of showers and thunderstorms. Prefer to keep it dry for Tuesday. Another cold front for Wednesday and the chance of showers and thunderstorms. Thursday and Friday remain up in the air. If a deep cyclone does develop and remains in the vicinity of the NE CONUS, then the combination of cooler air aloft and daytime heating/destabilizing boundary layer below, along with continued impulses through the cyclonic flow, could yield a setup for diurnally-forced storms. But it is possible that drier air and high pressure win out. Toss up at this point and subsequently a low confidence forecast. For Labor Day Weekend, going by ensemble means, it does appear the trough-ridge-trough pattern across the CONUS shifts subtly E thereby putting the NE CONUS at least the influence of high pressure. As to airmass depends on the preferred wind flow aloft (i.e., NW vs. SW). No threats or impacts just yet to speak of throughout the long-term forecast, as well as no end in sight with regards to current drought conditions. && .AVIATION /19Z FRIDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Saturday Night/... Through this evening...High Confidence. A cold front moves across the region. Scattered showers will affect RI and SE Mass with brief MVFR cigs near 2500 feet and vsbys near 4 miles. But most of the time will be VFR. Winds will be southwest ahead of the cold front and northwest behind. Gusts near 20 knots ahead of the cold front and 15 knots behind. Tonight...Moderate-High Confidence. Generally VFR with clearing skies and northwest winds becoming light. Radiational cooling will allow the more prone areas to develop fog patches with IFR/LIFR cigs and vsbys after midnight. Saturday...High Confidence. VFR. Light north winds, with seabreezes developing along both coasts. Saturday night...High Confidence. VFR. Light variable wind. Patchy fog after midnight in the usual prone locations with IFR/LIFR cigs/vsbys through sunrise. KBOS Terminal...VFR. Sea breeze likely around 15Z Saturday. High confidence in TAF. KBDL Terminal...VFR. High confidence in TAF. Outlook /Sunday through Wednesday/...Moderate Confidence. Sunday... Will keep it VFR with winds turning S becoming breezy. Increasing mid-high cloud across the region with the possibility of SHRA N/W late in the period. Monday... Chance of SHRA/TSRA. S/SW winds, breezy with gusts up to 20 kts, backing out of the W/NW towards Monday evening. Tuesday... Will prevail VFR with W/NW winds initially veering out of the S/SW. Anticipating increasing mid to high cloud late in the period. Wednesday... Chance of SHRA/TSRA. S/SW winds, breezy with gusts up to 20 kts, backing out of the W/NW during the evening into overnight period. && .MARINE... 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. Cold front moves across the waters early tonight. High pressure builds over New England Saturday. Winds and seas expected to remain below small craft advisory thresholds through Saturday night. Gusty southwest winds early tonight shift northwest, then become light north Saturday. Local seabreezes likely Saturday near shore. Light variable wind Saturday night. Seas 4 feet or less through the period. Outlook /Sunday through Wednesday/... Sunday... High pressure departing E. Winds turning S becoming breezy with gusts up to 20 kts. Will keep wave heights below 5 feet even with the swell associated with Gaston. Monday... Chance of showers and thunderstorms, mainly over the near-shore waters. S/SW winds, breezy with gusts up to 20 kts continuing, backing out of the W/NW towards Monday evening with a cold frontal passage. Persistent wind stress plus swell associated with Gaston, will introduce 5 foot seas on the outer waters. Tuesday... W/NW winds initially, fairly benign, veering out of the S/SW through the day. Will keep it dry. Continued swell from Gaston, will keep with 5 foot seas on the outer waters. Wednesday... Another cold front and another chance of showers and thunderstorms. S/SW winds ahead of the front with gusts up to 20 kts, backing out of the W/NW into the evening and overnight period. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...WTB/Sipprell NEAR TERM...WTB SHORT TERM...WTB LONG TERM...Sipprell AVIATION...WTB/Sipprell MARINE...WTB/Sipprell

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