Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 270236 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 1036 PM EDT Wed Jul 26 2017 .SYNOPSIS... Our relatively short spell of fair weather will come to an end tonight and Thursday...as a slow moving cold frontal boundary will push south from Ontario with some showers and thunderstorms. Expansive high pressure will then build across the Upper Great Lakes in the wake of the front...and this will provide most of us with fair weather on Friday. A dynamic storm system over the Mid Atlantic region will have to watched though...as significant rains are anticipated just to our south. && .NEAR TERM /THROUGH THURSDAY/...
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Our short stretch of fair weather will come to an end tonight and Thursday...as a slow moving cold front over southern Ontario will gradually settle to the south through our region. As of 03z...a swath of showers associated with this boundary was already crossing lake Ontario and the adjacent counties. Do not anticipate significant QPF from this activity...as rainfall amounts should generally be under a tenth of an inch. It will be milder tonight with temperatures only falling into the low to mid 60s. On Thursday...the weak cold front will settle south through the region. Will go with a slower timing of the front over the warmer lake waters...and with surface high pressure still aways off over the northern Plains and western Great Lakes. Chances for storms through the morning hours will become greatest during the afternoon...coinciding with the peak heating of the day (SBCAPE values up to 2000 J/KG) and cold front passage. Bulk wind shear will be weakening through the day, and severe threat at this time will remain marginal across the region. Highs Thursday will run close to normal for the region.
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&& .SHORT TERM /THURSDAY NIGHT THROUGH SATURDAY NIGHT/... Any left over showers Thursday evening will slowly dissipate across the region as the airmass starts to dry up following the frontal passage. Surface winds will veer to the north/northeast with an overnight low temperature in the mid 60s across Western New York and upper 50s across the North Country. Mostly cloudy skies may prevail toward Friday morning as the low level environment remains relatively moist. On Friday, an upper level trough over Saskatchewan will amplify as it moves ESE across the Northern Plains and into the Upper Great Lakes. At the surface, weak surface ridging will begin to slide southeastward with a 1022mb high centered over Lake Superior. Strengthening northeasterly winds with still relatively moist low levels should promote a fair amount of upslope cloudiness across the region. Given cool temperatures and strong northeasterly flow, high resolution guidance has backed off on any afternoon convection forming along lake-breeze boundaries. Therefore, Friday should be dry for most locations. The one exception might be toward the Southern Tier/PA border due to lift from the upper level low moving toward the OH Valley. Daytime highs should be cooler than Thursday and generally end up in the low 70s. Friday night...There will still be a low chance for showers in the Southern Tier/PA border, as the latest models are still in discrepancy with the placement of the low that will have moved into the OH valley Friday evening. More than likely the low will be located over the Ohio/Pennsylvania border. The overnight low temperature should end up in the mid to upper 50s except for along the lakeshore where temps may hover near 60. By Saturday, strong 500mb ridging will slide from the Central Plains into the northeast and over the region. At the surface, a 1022mb high will move in and end up park right over the Great Lakes through the entire weekend. There may be some clouds toward the south from the old low, now somewhere over the Mid Atlantic, but overall upper level ridging and high pressure will push into the region providing for a dry Saturday. 850mb temperatures are forecast to be near +9/+10C. This, combined with relatively strong northeasterly winds picking up ample lake moisture off both of the lakes, should result in at least some clouds early near Lake Ontario. Temperatures will remain in the 60s with a daytime high in the upper 60 with comfortable humidity levels. Saturday night will have quiescent conditions with a low in the mid 50s under strong high pressure. This pattern should provide ideal conditions for river valley fog late Saturday night. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... Picture perfect weekend weather remains on tap for all of western NY and the North Country. Ridging builds into the region Sunday with warming 850 mb temps back into the low teens C, which will push our afternoon highs back to near normal with highs around 80. Sunday will feature more abundant sunshine as high pressure builds overhead. Model solutions diverge for the start of next week with differences in the magnitude of a trough over eastern Canada. A stronger trough may force a weak cold frontal passage through the area with some scattered showers and a very subtle few degrees cooler in temperature to near normal. A weaker trough would keep the stretch of dry weather going from the weekend right into the early next week with slightly above normal temperatures. && .AVIATION /03Z THURSDAY THROUGH MONDAY/...
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A 50 mile swath of showers over Lake Ontario at 03z will slowly push south across parts of western New York during the course of the night. While cigs will lower from 10k ft with this activity...mainly VFR conditions are expected to persist. On Thursday...additional showers and possible thunderstorms can be expected as a slow moving cold front will push through the region. Cigs are expected to deteriorate to MVFR levels for most areas. Outlook... Thursday night...Mainly VFR. Friday through Monday...Mainly VFR.
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&& .MARINE... Departing surface high pressure will maintain minimal waves and winds on the lakes and rivers through tonight. A cold front will slowly pass across the waters on Thursday, with southwest winds increase on the eastern end of Lake Ontario to 15 to 20 knots and waves building to around 4 foot. Behind this front, winds and waves will increase some as cold air on a northerly flow pours over the lakes. Winds will increase, and though wave heights will fluctuate some, they will near 5 feet along the southern shoreline of Lake Ontario Thursday night through Friday night. Later Saturday and then through the weekend high pressure over the Eastern Great Lakes will bring fine boating conditions continuing through the weekend as high pressure slowly passes by. && .TIDES/COASTAL FLOODING... An intensifying storm system over the Middle Atlantic states later in the week will combine with high pressure over the Upper Great Lakes to produce a prolonged period of fresh northeasterlies on Lake Ontario from late Thursday night through Friday. While winds and waves may temporarily subside late Friday...winds are forecast to become northerly and increase during the first half of Friday night. The risk is increasing that waves could build to levels that may produce additional erosion and flooding along much of the south shore of the lake. A new lakeshore flood watch has been issued from Niagara county to Wayne county to cover this heightened risk. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Lakeshore Flood Watch from Friday morning through late Friday night for NYZ001>004. MARINE...None. && $$ SYNOPSIS...RSH NEAR TERM...RSH/THOMAS SHORT TERM...ZAFF LONG TERM...CHURCH AVIATION...RSH MARINE...THOMAS TIDES/COASTAL FLOODING...RSH

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