Area Forecast Discussion
Issued by NWS Buffalo, NY
Issued by NWS Buffalo, NY
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975 FXUS61 KBUF 260235 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 1035 PM EDT Wed Sep 25 2024 .SYNOPSIS... A weak low pressure system will slowly drag a cold front through the area with chances for showers tonight into Thursday. Areas east of Rochester may experience some left over showers through mid morning Thursday...otherwise high pressure will build across the Lower Great Lakes to support fair dry weather through at least Friday. Most... if not all...of the significant rains from Helene should stay to our south. && .NEAR TERM /THROUGH THURSDAY NIGHT/... A weak low pressure system will ever so slowly lift north through Quebec while dragging a wavy cold front through tonight into Thursday. Deep rich moisture streaming forward along and ahead of this boundary (PWAT 1.5") will be lifted by a combination of a 110kt H25 jet rotating around the base of a vigorous northern stream shortwave and convergence in the lower levels. This will bring once again, after a brief lull, another round of showers...some of which could be locally heavy. Rainfall amounts tonight are forecast to range from a quarter to a half inch in most basins...with the lesser amounts expected to be over the Finger Lakes region. Elevated CAPE of 200-400 j/kg will be found within this environment...so will maintain the chance for thunderstorms. While the showers will taper off from west to east late tonight as the mid level moisture gets stripped away...a wealth of cloud cover will persist. The slow moving front will certainly take its time exiting the Eastern Lake Ontario Thursday morning...so likely to cat pops will remain in place for the initial daylight hours. Meanwhile...s l o w clearing will start to take place back across the IAG Frontier. As we push through the midday and afternoon...the residual showers will come to an end with more pronounced clearing taking place further west due to more effective diurnal mixing and strengthening subsidence from sfc based ridging. High pressure centered to the north of Lake Ontario Thursday night will then guarantee fair dry weather...although some cloudiness may still linger near the Pennsylvania border. It will be notably cooler...with mins forecast to be in the low to mid 50s...rather than the 60s from the previous two nights. && .SHORT TERM /FRIDAY THROUGH SUNDAY NIGHT/... Friday through Saturday, the eastern Great Lakes will be sandwiched between two areas of low pressure aloft: one closed moving east across the Canadian Maritimes, and another meandering over the Mississippi Valley. It is the latter that will need to be watched for the potential for showers moving towards the end of the week. As Helene`s remnants move northward across the Southeast states, a Fujiwhara interaction will cause the tropical low to turn northwest before becoming absorbed by the pre-existing closed low. Further north, a flattening ridge of high pressure and mid-level dry air will squeeze across our forecast area between this complex low to the southwest and the departing trough to the northeast. The center of the southern mid-level circulation is then expected to slowly wobble northward towards the Ohio Valley, partially open into a longwave trough, and progress eastward towards the Mid-Atlantic states by Sunday night. While the thin ridge of high pressure is expected to keep our region entirely dry through at least Friday, there remains uncertainty in the potential for showers Friday night and beyond. As the complex low over the Mississippi Valley circulates a band of deeper moisture northward towards the lower Great Lakes, it will run up against the overhead area of high pressure, stall out, and become increasingly removed from the stronger upper jet energy on the eastern periphery of the low. The majority of the precipitation expected to approach from the south with this system is therefore expected to fizzle out as it nears the NY/PA border and moves across Lake Erie, though there are enough signals from the latest guidance that suggest some of this activity will survive the journey over the southern CWA border. Low confidence in timing and overall coverage of showers at this range so PoPs remain on the low side, though best chances for precip look to be in the Southern Tier late Friday night and Saturday afternoon, though can`t completely rule out the occasional shower south of I-90 through Saturday night, while Sunday and Sunday night look to be comparatively drier. Outside of the chances for rain...Temperatures Friday and through the weekend will continue to run on the warm side, with highs in the low to mid 70s in most spots, a few readings in the 60s on the hilltops. Lows will generally range from the low 60s close to the Lake Erie shoreline to the upper 40s across the hilltops east of Lake Ontario, with a range of 50s in between. && .LONG TERM /MONDAY THROUGH WEDNESDAY/... The longwave pattern will continue to be dynamic through mid-week, with more unsettled weather re-emerging. By Monday, the remnants of Helene will be circulating within the partially open, positively tilted wave over the Ohio Valley and Mid- Atlantic states. This could lead to a few showers across the far Southern Tier Monday, though high pressure ridging to the north should keep conditions mostly dry. Meanwhile, a robust secondary mid-level trough will be racing east across the Northern Plains and into the Upper Midwest. As it does so, the two troughs will phase and deepen over the Great Lakes. This will drive a strong cold front through the forecast area sometime late Tuesday into Wednesday, with the remnant moisture from Helene providing ample fuel for widespread showers. Significant timing differences among the models preclude higher PoPs this update but could see this changing once the details come into better focus. Have stuck close to NBM for now, with gradually increasing chances for showers from west to east Monday night through Tuesday, then tapering down some for Wednesday. While temperatures are expected to continue to average above normal Monday and Tuesday, much cooler air in the wake of the front will finally give us a taste of true fall weather by Wednesday. Models are far from lock and step with the depth of the cooler airmass, though ensemble mean 850H temps are around +6C by Wednedsay which should translate to highs in the 50s to low 60s. This will also be plenty cold enough to potentially spur some additional lake effect rain showers Wednesday, though the airmass may be initially too dry for this to be realized. && .AVIATION /03Z THURSDAY THROUGH MONDAY/... A slow moving cold front will bring another round of showers through the region tonight...with a mixture of VFR/MVFR to IFR cigs...the latter of which will be focused across the Srn Tier. While showers will persist east of Rochester Thursday morning...fair dry weather will return to the region. Cigs will improve to VFR levels by late morning/midday...then most areas will lose their cigs altogether by the end of the day. Outlook... Thursday night...Mainly VFR. Friday...Mainly VFR...but with a chance of showers across the western Southern Tier. Saturday through Monday...VFR. && .MARINE... A modest pressure gradient across the lakes will produce enough wind and wave action to continue SCA on Lake Ontario tonight. Winds will gradually become southwest and then west late tonight through Thursday as a trough crosses the eastern Great Lakes from west to east, with wind speeds decreasing with the passage of the trough. Northeast flow will then pick up Friday, possibly requiring small craft headlines on Lake Erie and western Lake Ontario. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...Small Craft Advisory until 2 AM EDT Thursday for LOZ045. && $$ SYNOPSIS...AR/RSH NEAR TERM...AR/RSH SHORT TERM...PP LONG TERM...PP AVIATION...AR/RSH MARINE...AR