Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 252314 AFDBOX Area Forecast Discussion National Weather Service Taunton MA 714 PM EDT THU AUG 25 2016 .SYNOPSIS... High pressure offshore brings warm and humid conditions tonight. A cold front swings through the region Friday, bringing showers and a few thunderstorms later tonight and Friday. Seasonable and dry for the weekend. Chance of scattered showers and thunderstorms for Monday. Thereafter dry weather Tuesday into Wednesday. From then on possibly into the Labor Day Weekend a more disturbed, wet- weather pattern is forecast. Continue to monitor the latest with Invest-99L but the long-term track forecast remains uncertain. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... 730 pm update... Looking at the broad picture across the NE CONUS. Low to mid level heights lowering with the influx of mid-level energy across the NE CONUS. Still some component of anticyclonic flow aloft. Per BUFKIT profiles, majority of forcing is confined at or below H5, mainly within the low-levels with some association with mid-level weak vortex energy. Isallobaric response of S/SW winds gusting upwards of 25 mph ahead of a surface cold frontal feature presently into the E Great Lakes, plenty of moisture within the low-levels beneath H7. Precipitable waters up to 2 inches with surface dewpoints rising into the upper 60s to the 70 degree mark. Weak shear in an otherwise weakly unstable environment as lapse rates are poor aloft. Pre-frontal trough sweeping across the Hudson presently into New England, expect overnight chances of showers, with the greater likelihood of low clouds and possibly fog. Have gone ahead and removed the mention of thunder given the environment noted above. Have greater confidence of thunder chances into Friday as the cold front approaches ahead of which there is an opportunity for the boundary-layer to destabilize. Still, will have to keep an eye on activity emerging out of the E Great Lakes region. With boundary- layer decoupling, expecting winds to drop off but maintain a S/SW flow. Low temperatures limited by cloud cover and rising dewpoints. Values in the upper 60s to low 70s. But will have to monitor the possibility of clearing between the present pre-frontal trough and activity over the Great Lakes. If radiational cooling is allowed to proceed, especially for the interior sheltered valleys, could be contending with some fog given the higher dewpoints. && .SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/... Friday... First plume of moisture moves through in the morning. A second plume crosses in the afternoon along with the cold front. Shear continues marginal, with brief 35 knots at 500 mb midday. Instability builds with a couple of models showing 1000 J/Kg CAPEs. LI remains sub-zero. Continue showers/scattered thunder during the day. The high precip water values will allow for locally heavy downpours. Friday night... Cold front moves offshore Friday evening. The high precip water values decrease noticeably behind the cold front, as does the cloud-level moisture. Expect clearing skies and winds shifting from the Northwest. && .LONG TERM /SATURDAY THROUGH THURSDAY/... */ Highlights... - Seasonable and dry weekend, fantastic weather! - Shower and thunderstorm chances for Monday - Banking dry weather for early-mid week, wet-weather mid-late week - Low confidence forecast for next week especially with Invest-99L */ Discussion... Forecast hinges upon the morphology of synoptic features towards the later-half of the week into Labor Day Weekend with respect to Invest- 99L (AL99). Continued struggles with forecast model performance in handling N/E Pacific disturbances into the W CONUS is subsequently leading to alterations in the ridge-trough-ridge pattern extending from the Gulf of Alaska region into the Central and E CONUS. Notably atmospheric teleconnections have exhibited some waffling within the last few model runs, especially into the beginning of September. Do still believe through the complications that the H5 High presently across S/E CONUS and Mid-Atlantic will only shift and perhaps weaken with the presence of AL99. This yields the opportunity for pacific- origin energy through the consensus forecast of near-zonal flow for the early- to mid-week period to have a greater influence S across the N CONUS as AL99 makes its approach. Then it becomes a question of how such energy from the N interacts with the consensus forecast of AL99 into the SE CONUS towards the Mid-Atlantic. After a certainly pleasant, comfortable weekend with seasonably dry weather with likely onshore influences, looking at wet-weather for Monday with scattered showers and thunderstorms. Not overwhelming confident. Timing of associated cold frontal passage in question as is both the availability of moisture and instability. Weak shear profiles as lapse rates are poor. Seemingly still dealing with the lingering influence of high pressure. But if synoptic forcing can come together along with a destabilizing boundary-layer, outcomes are plausible, especially Monday afternoon. Will hold with chance PoPs over much of S New England. Continued low confidence forecast hereafter as deterministic models struggle with individual waves and accompanying influences through the ensemble-weighted near-zonal flow with favorable troughing in the vicinity of the W CONUS. Content with earlier thinking that beyond Monday will be a brief period of high pressure followed by periods of disturbed weather for the mid-late week period. Crucial is whether AL99 is wrapped into expected disturbed weather and N- stream energy late week into Labor Day Weekend to which the majority of guidance keeps offshore. But with some ensemble members that is not the case, and the consensus forecast has exhibited some wobbling as of late, so overall forecast outcomes remain uncertain. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/... 0z update... Tonight...Moderate confidence. Low-end VFR cigs with MVFR likely. Highest confidence MVFR across high terrain (i.e., ORH). Lot of moisture in the air, so will have to monitor for potential fog as well, perhaps after SCT SHRA sweep NW to SE during the overnight period. Potential SKC behind the line could yield fog. Not expecting TSRA. S/SW winds gusting initially 20 to 25 kts will diminish during the evening period. Friday...Moderate Confidence. SCT SHRA/TSRA, with higher confidence over S/E interior S New England terminals. S/SW winds continue with gusts up to 20 kts before shifting out of the NW late. Low-end VFR cigs but can not rule out MVFR, with TEMPO MVFR-IFR conditions with any TSRA and/or +RA. Friday night...Moderate Confidence. SW winds shifting out of the W/NW, 10 kts or less. VFR with the possibility of IFR conditions prior to the wind shift over S/E coastal terminals. Will also need to monitor whether light winds and radiational cooling can yield interior fog issues. KBOS Terminal...prevail -SHRA overnight. Towards 15z onwards will be closely watching areas S/W for TSRA development. SW winds overall with gusts around 20 kts during midday Friday into afternoon. KBDL Terminal...low-end VFR to MVFR possible overnight. Clearing into Friday morning, potentially, will be monitoring for TSRA development around and E of the terminal midday into afternoon. Outlook /Saturday through Tuesday/... Saturday into Sunday...High Confidence. VFR. Light winds. Likely sea-breezes. Winds turning E/SE Sunday, potentially breezy late with SCT mid-high cloud. Monday...Moderate Confidence. Chance of SHRA/TSRA. Timing of outcomes remains unclear at this time, could see some morning activity followed by afternoon storm development. S/SW winds, breezy with gusts up to 20 kts, backing out of the W/NW towards morning. Tuesday...Moderate Confidence. Will prevail VFR with winds turning out of the W/NW. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. Short Term /through Friday Night/...High confidence. 730 pm major changes to the forecast. Tonight... Winds 20 to 25 knots this evening should diminish during the night. Seas will remain below 5 feet. A small craft advisory remains in effect through the evening due to the wind potential being near 25 knots. Friday... Cold front approaches late tonight and Friday with potential for showers and scattered thunderstorms. This will bring briefly lower vsbys. Also areas of fog possible early Friday with lower vsbys. Winds below 20 knots or less, seas 4 feet or less. Friday night...Moderate Confidence. SW winds 10-15 kt Friday evening, with gusts up to 20 kt on the southern waters, shifting to N-NW overnight as a cold front sweeps the waters. Seas 4 ft or less. Patchy fog on the S near shore waters with visibility restrictions. Outlook /Saturday through Tuesday/... Saturday into Sunday...High Confidence. High pressure, light winds, gradually veering out of the S/SE into Sunday, becoming breezy late. Waves remaining below 5 feet. Monday...Moderate Confidence. Winds turning out of the S/SW ahead of a sweeping cold front. There is the potential for gusts up to 20 kts. This in addition to shower and thunderstorm activity, mainly considering the near-shore waters. Expect the cold front to sweep the waters towards the later half of the day, into evening, at latest overnight. Wave influence per weather may be minimal, but of greater concern is swell associated with Gaston. Waves in excess of 5 feet by evening. Tuesday...Moderate Confidence. Cold front pushing out to sea as winds back W/NW. Swell continuing from Gaston with wave heights up to 6 feet on the outer waters. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 11 PM EDT this evening for ANZ231>235-237-250-251-254>256. Small Craft Advisory until 10 PM EDT this evening for ANZ236. && $$ SYNOPSIS...WTB/Sipprell NEAR TERM...WTB/Sipprell SHORT TERM...WTB LONG TERM...Sipprell AVIATION...WTB/Sipprell MARINE...WTB/Sipprell is the U.S. government's official web portal to all federal, state and local government web resources and services.