Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 250254 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 1054 PM EDT Wed May 24 2017 .SYNOPSIS... An upper level low will track across the region tonight and tomorrow, spreading a period of rain late tonight and then through Thursday across the region. This period will taper off to scattered showers during the afternoon across Western New York, and then the evening across the North Country. Temperatures will remain below normal through Friday as the upper level low and trough pass through. && .NEAR TERM /THROUGH THURSDAY NIGHT/... An upper level low across the Ohio Valley will gradually move toward the region overnight. An initial wave from this system just clipped the Niagara Frontier earlier this evening. The next (and more significant) wave of rain will continue to spread across WNY overnight with high forecast confidence in rain south and west of Rochester. Deep layer convergent lift from both the leading edge of a 45 to 50 knot LLJ around 4K feet, and upper level divergence from the left exit region of a 130 knot upper level jet streaking along the eastern seaboard. This broad scale lift ahead of the upper level low, within an environment with PWAT values between 1.0 and 1.5 inches, will bring a period of moderate rain across our region. This is supported by a consensus of model guidance and radar trends. As the LLJ carries northward through the day Thursday, expect the main slug of rain to into the North Country Thursday morning and then northward into Canada in the afternoon. This will leave just spotty showers across Western New York Thursday afternoon and early evening as the upper level low tracks across the region. Behind the upper level low Thursday night a westerly flow within an inverted surface trough will bring scattered showers across the region. Aloft there will still remain a trough, supporting the showers. An upslope flow within a still saturated low level will bring likely pops across the Chautauqua Ridge, and hills across SW NYS. This lower saturated layer will also bring low clouds Thursday night, of which some will produce patchy fog, mainly across the hill tops of SW NYS. Overall rainfall tonight through Thursday night will average around an inch, slightly higher towards the Niagara Frontier where a downslope SE flow slowing over northern Erie and Niagara County may enhance rainfall totals, while slightly under an inch of rain is expected across the North Country. Temperatures at night will dip into the 50s, warmest tonight across the lake plain where a southeast will maintain upper 50s. Highs Thursday will remain below normal as the upper level low tracks across the region, with temperatures rising into the lower to mid 60s. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... Mid level low pushing through New England Friday. This will allow shower activity to gradually diminish through the day, with only some lingering shower activity in northwest upslope flow and wrap around moisture. Friday will be a cool day with plenty of cloud cover and scattered precipiation, with most highs in the upper 50s to mid 60s. Shortwave ridging should bring an end to the precipitation by early Friday night. The shortwave ridge will crest across the forecast during the day Saturday, providing for what should be a dry day for Western and North-Central New York. Saturday will be a warmer day under a weak warm air advection pattern and increased sunshine. Most highs in the lower 70s. Precipitation chances look to increase later Saturday night as upper low level drops out of central Canada. The associated surface low moves into the Ohio Valley by Sunday morning. Associated height falls, forcing and moisture advection on the front flank of the system will bring precipitation back into far western areas beginning late Saturday night. && .LONG TERM /SUNDAY THROUGH WEDNESDAY/... Precipitation chances look much more favorable on Sunday, as an upper level trough over the central Rockies phases with a potent shortwave dropping out of Saskatchewan, resulting in yet another broad low pressure system that will move across the Great Lakes during the latter half of the weekend into the beginning of next week. Falling heights and strong isentropic uplift on the eastern flank of the approaching low should provide for another widespread soaking rain Sunday, with showers once again lingering through Monday and Tuesday as the large system meanders across the region, with multiple upper level impulses passing overhead. Temperatures will run in the upper 60s to low 70s Sunday into Monday. Cooler air will filter into the region by Tuesday into Wednesday , as the axis of the upper level trough begins to meander overhead. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... VFR conditions in place late this evening will gradually deteriorate overnight as rain overspreads the region. CIGS will lower to MVFR (and IFR in spots) as this rainfall persists and moistens the boundary layer. The lowest conditions are likely to occur Thursday morning with the steadiest rains and when the flow is ENE across the area. This flow can result in IFR CIGS at BUF/IAG/ROC, but only partially taps into upsloping which would be more significant in a NE flow rather than an ENE one. A period of IFR conditions is also likely at JHW due to its higher elevation. A modest improvement in CIGS is likely Thursday afternoon as the steady rain tapers off. Even so, expect widespread MVFR conditions with patchy IFR CIGS possible. Outlook... Thursday night and Friday...MVFR/IFR with scattered showers. Saturday...Mainly VFR. Sunday...MVFR/VFR with showers likely. Monday...MVFR/VFR with a chance of showers. && .MARINE... Low pressure will slowly track from he Ohio Valley to near the lower Great Lakes and Western Pennsylvania through Thursday. This will result in an increasing ENE flow to around 15 to 25 knots on the western end of Lake Ontario. These are not ideal for building waves in the nearshores, but should be ample for waves to reach 3 to 6 feet on the western U.S. shores, with the highest waves in Canadian waters. There is a small craft advisory in effect for western nearshores of Lake Ontario. As the upper level low crosses the lower lakes Thursday night the winds and waves will diminish on both lakes. && .TIDES/COASTAL FLOODING... A deepening low pressure system will move closer with an increasing ENE flow on Lake Ontario. Winds will increase to 15 to 25 knots on Thursday, allowing waves to build to 3 to 6 ft by Thursday afternoon. Given the high lake levels, this is expected to generate lakeshore flooding from Monroe county west to the Niagara River, with additional shoreline erosion likely. A Lakeshore Flood Warning is in effect from Thursday morning through Thursday evening. The higher wave action and associated flooding risk should be relatively short-lived, however. The low will move over head Western New York by Thursday evening, resulting in sharply diminishing winds, with waves subsiding shortly thereafter. A baggy pressure gradient on the back side of the departing low means that while northwesterly flow behind the low should generate some choppy conditions Friday along the southern shores of Lake Ontario, waves should remain in the 1-2 foot range, and additional flooding issues are not expected. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Lakeshore Flood Warning from 8 AM Thursday to 2 AM EDT Friday for NYZ001>003. Beach Hazards Statement from 8 AM EDT Thursday through Thursday evening for NYZ001>003. MARINE...Small Craft Advisory from 6 AM to 11 PM EDT Thursday for LOZ043. Small Craft Advisory from 6 AM Thursday to 2 AM EDT Friday for LOZ042. && $$ SYNOPSIS...THOMAS NEAR TERM...APFFEL/THOMAS SHORT TERM...THOMAS LONG TERM...CHURCH/WOOD AVIATION...APFFEL MARINE...APFFEL/THOMAS TIDES/COASTAL FLOODING...HITCHCOCK/WOOD/APFFEL

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