Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 230253 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 1053 PM EDT Tue Aug 22 2017 .SYNOPSIS... Showers and thunderstorms will end from west to east late this evening, as a cold front crosses the area. Much cooler weather will then build into the region for Wednesday through the weekend with a few spotty showers possible Wednesday and Thursday. High pressure will then bring dry weather Friday through the weekend. && .NEAR TERM /THROUGH WEDNESDAY/... The final line of showers marking the cold frontal boundary which extends from a surface low over southwestern Quebec is crossing the forecast area late this evening. This front is pushing into western New York, and will continue to sweep across the area overnight, causing temperatures to fall into the upper 50s to around 60 by daybreak. Post-frontal subsidence will suppress any lake-effect clouds/precipitation, and as such expect clearing and drying once this last line of showers moves through. The axis deep upper level trough that has been driving the unsettled weather across our region will be making its way into the lower Great Lakes through the day on Wednesday. The combination of diurnal instability being enhanced by falling heights aloft, lake enhancement due to the increasing sfc-850mb delta-t on the lakes, which will be increasing to +14C, and DPVA as a vorticity lobe associated with the trough approaches the region may result in the development of increased clouds and scattered showers in the afternoon. The fly in the ointment however will be a lack of deep synoptic moisture. As such, while it should be more cloudy than sunny in the afternoon, the actual chance of showers will remain relatively low, around 30 percent. Temperature-wise, the effects of the cold frontal passage will be quite noticeable, producing a much more comfortable day across the area, with highs in the low 70s, and substantially less humidity, as dewpoints will fall into the low 50s. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... The main feature of note during this period will be an upper level trough that will be in place across the northeastern U.S. through the period. A pair of shortwaves dropping out of Canada will reinforce the troughing across the region, and with 850mb temps falling to +6C generating a robust lake response, we can expect fairly widespread cloud cover at least through Thursday. Shower chances south/southeast of the lakes will only run to about 30 percent at best though, as there will be a dearth of moisture aloft. It start to feel fall-like temperature-wise, with the trough causing temperatures to fall into the upper 40s to mid 50s both Wednesday night and Thursday night, with highs only reaching the upper 60s Thursday. Expect sunnier skies to end the work week on Friday, as the latest shortwave passes to the east and surface high pressure begins to build in from the upper Great Lakes. The corresponding subsidence and very dry airmass, along with light winds aloft, should outweigh lingering lake instability to provide for a brighter end to the week, though it will remain on the cool side, with highs in the upper 60s. && .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/... A pleasant weather pattern is expected over the weekend and heading into next week. Model consensus (ECMWF/GGEM/GFS) builds surface high pressure across the region throughout the entire long term period. This will result in a prolonged stretch of dry weather, with partly to mostly clear skies. The back edge of an upper level trough will pivot across the region Saturday night and Sunday. With 850 mb temperatures falling to around +6C there may be some lake effect clouds, and the shortwave may spark a stray shower. This said, the dry air mass will limit the potential for anything more than widely scattered showers. Otherwise, the cool air mass will result in cool, almost fall-like temperatures. Over the weekend highs will average in the lower 70s with overnight lows falling well into the 40s across the interior valleys. Temperatures will warm slightly early next week, with highs in in the lower to mid 70s. && .AVIATION /03Z WEDNESDAY THROUGH SUNDAY/... Final rounds of showers are crossing the forecast area this evening, immediately ahead of a cold front, which will cross the forecast area overnight. Aside from a brief period of MVFR/IFR conditions as the showers move through, look for improvement to VFR behind the cold front as drier air advects into the region. VFR conditions will prevail during the day on Wednesday, though an increase of diurnal/lake-enhanced stratocu is expected during the afternoon, with scattered -shra possible as an upper level trough axis makes its way into the lower Great Lakes. Outlook... Wednesday night and Thursday...VFR/MVFR with a chance of showers. Friday through Sunday...VFR. && .MARINE... A cold front is currently crossing the lower Great Lakes, and will continue to cross the region overnight. The strong southwesterly winds earlier today have diminished this evening, and the small craft advisories in effect for the Niagara and St. Lawrence rivers have been ended. However, westerly winds will remain strong enough in the wake of the frontal passage to leave SCA headlines in place for Lake Erie through the rest of the evening. Westerly winds behind the front will have a long enough fetch on Lake Ontario to keep waves in the 4 to 7 foot range on the eastern half of the lake through the day on Wednesday, warranting a continuation of SCA headlines into Wednesday evening, at which point winds should diminish as the low pressure system responsible for the winds pulls away from the region and high pressure begins to build in from the upper Great Lakes. Thereafter, fairly tranquil conditions, with waves 2 feet or less, will be found on the lakes through the rest of the work-week, as high pressure slides across the region. && .TIDES/COASTAL FLOODING... Westerly winds will freshen in the wake of a cold frontal passage tonight and will remain strong through Wednesday. The increase in winds and wave action will bring and increase in shoreline erosion and lakeshore flooding to the east half of Lake Ontario when combined with the already high lake levels. The static lake levels have dropped since late spring and early summer, so the impacts of this event are not likely to be as significant as earlier in the season, but still enough to warrant a Lakeshore Flood Warning. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Lakeshore Flood Warning until 11 PM EDT Wednesday for NYZ004>007. Beach Hazards Statement from 6 AM EDT Wednesday through Wednesday evening for NYZ003. Beach Hazards Statement from 6 AM EDT Wednesday through Wednesday afternoon for NYZ002. MARINE...Small Craft Advisory until 2 AM EDT Wednesday for LEZ040-041. Small Craft Advisory until 6 AM EDT Thursday for LOZ042>045. && $$ SYNOPSIS...HITCHCOCK/SMITH/WOOD NEAR TERM...WOOD SHORT TERM...WOOD LONG TERM...APFFEL AVIATION...WOOD MARINE...WOOD TIDES/COASTAL FLOODING...HITCHCOCK/WOOD

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