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Area Forecast Discussion
Issued by NWS Buffalo, NY
Issued by NWS Buffalo, NY
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297 FXUS61 KBUF 161459 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 1059 AM EDT Fri Aug 16 2024 .SYNOPSIS... High pressure draped across central and eastern New York will slowly drift east to New England today. This will keep fair weather in place through most of today...with just a chance of showers and thunderstorms reaching far western New York later in the day. A large...slow moving storm system will then track across the region and bring periodic rounds of showers and scattered thunderstorms tonight through Monday...with locally heavy rainfall and a few stronger storms possible over the weekend. Otherwise temperatures will remain near to above normal through the weekend...before falling below normal early next week. && .NEAR TERM /THROUGH TONIGHT/... Today surface high pressure across central and eastern New York will drift out across New England...while a vertically stacked and increasingly expansive storm system slowly makes its way across the Upper Great Lakes. Out ahead of this system broad upper level ridging will crest across our region this morning...before sliding east into eastern New York/western New England during the afternoon. The combination of lingering plentiful dry air and subsidence attendant to the upper level ridge should help to keep our region dry through the midday to early afternoon hours...with just a general west to east increase in mid and high cloud cover that will be most pronounced west of the Genesee Valley. As the upper ridge axis slides further east during the afternoon...increasing moisture out ahead of the approaching low will result in mid and high cloud cover continuing to increase and lower from west to east. Coupled with daytime heating and the arrival of some weak lift on the eastern periphery of the low...this may allow for some scattered showers and thunderstorms to develop across far western New York during the late afternoon and early evening hours...though coverage should remain on the limited side through 22/23z. With respect to temperatures...the warm airmass out ahead of the low and a modest south to southeasterly low level flow will allow for another warm day...with highs ranging from the upper 70s to mid 80s across far western New York to the mid to upper 80s across much of the Finger Lakes and eastern Lake Ontario region...where more sunshine is expected. Tonight the center of the large storm system will make its way into northern Lower Michigan...and in the process will push its attendant warm front into our region...with this latter feature roughly making it to about the south shore of Lake Ontario by 12z Saturday. This boundary will be accompanied by a surge of GOMEX-based moisture attendant to a 30+ knot low southerly level jet that will push precipitable water values up into the 1.5-2 inch range. At the same time...isentropic upglide out ahead of the warm front...convergence at the nose of the low level jet...and a broadly diffluent flow regime aloft will all combine to lift this deepening moisture field...thereby leading to a round of showers and scattered thunderstorms that will work across the area from west to east through the course of the night. Given the quality of the forcing and moisture that looks to be in place have raised PoPs into the categorical range... with most of western New York likely to pick up basin-average rainfall amounts of a quarter to a half inch before the warm frontal pcpn begins to wind down across far WNY late in the night. Owing to the above...also cannot completely rule out some locally heavier rainfall/limited flooding risk...as reflected by the Marginal Risk across western New York in WPC`s Day 1 Excessive Rainfall Outlook. Otherwise it will be a notably warmer and more humid night...with lows ranging from the low-mid 60s east of Lake Ontario to the mid 60s to lower 70s elsewhere...and surface dewpoints rising into the lower to mid 60s. && .SHORT TERM /SATURDAY THROUGH MONDAY/... The longwave pattern across the CONUS will amplify over the weekend, with a strong ridge building over the Rockies and High Plains, forcing a deep longwave trough to carve out over the eastern third of the nation. A mid level closed low found within the deepening longwave trough will meander very slowly east across the central Great Lakes Saturday through Sunday before finally reaching the eastern Great Lakes Monday. A weak surface low will remain vertically stacked beneath this mid level feature through the period. PWAT values will run in the 1.5" to 1.75" range much of the time, with persistent forcing and moisture bringing an extended period of unsettled weather Saturday through Monday. Saturday, the initial push of moisture transport and convergence near the nose of a 35+ knot low level jet will provide the focus for an organized area of showers moving from the Genesee Valley and Finger Lakes early in the morning into the eastern Lake Ontario region through the day. Emerging consensus of operational guidance suggests a lull in rain chances across Western NY for a time Saturday behind this initial wave of showers. DPVA and height falls will continue to spread east out of the Central Great Lakes Saturday afternoon, combining with ample moisture and diurnal instability to bring increasing coverage of showers and a few thunderstorms again in the afternoon and evening. Saturday night through Sunday, ongoing height falls and numerous convectively augmented vorticity maxima propagating through the longwave trough will continue to bring periodic enhanced ascent, supporting numerous rounds of showers and a few thunderstorms. Sunday night through Monday, the closed low will gradually deamplify into an open wave, but ongoing forcing and deep moisture will still support occasional showers through the start of the work week. Thunder chances will gradually wane from northwest to southeast as better instability moves to the east coast. Potential Hazards... SPC has much of the area in a Marginal Risk for severe thunderstorms both Saturday and Sunday. Flow will be relatively weak through the period with low end shear values for more organized modes of convection. Some diurnal instability will develop both days, although poor mid level lapse rates will limit updraft strength. Expect an isolated risk of damaging winds with any organized multi- cell clusters, with the risk peaking in the afternoon and early evening each day. The persistent moisture and forcing also suggests a potential for localized heavy rainfall and an isolated flash flood risk later Saturday through Sunday night, particularly in areas where convection repeats. WPC has a Marginal Risk of excessive rainfall Saturday through Sunday. && .LONG TERM /MONDAY NIGHT THROUGH THURSDAY/... Monday night through Tuesday the trough axis will finally move just east of our longitude, with the plume of deep moisture on the eastern flank of the trough drifting to the east coast. Surface high pressure will build into the upper Great Lakes Tuesday, then expand south and east to cover the entirety of the Great Lakes, Ohio Valley, and Northeast Wednesday through Thursday. A few showers may linger into Monday night, particularly in Central NY and the eastern Lake Ontario region. Thereafter, dry weather will prevail from Tuesday through the end of next week. The airmass is quite cool initially, with highs Tuesday only around 70 for lower elevations and 60s for higher terrain. The airmass will then gradually modify through the rest of the week. Nights will be cool with high pressure and a cool airmass overhead. This will translate into 50s close to the lakes and 40s inland each night from Monday night through the end of next week. && .AVIATION /15Z FRIDAY THROUGH TUESDAY/... High pressure will slide off to our east this afternoon...while the next storm system will drop across the Upper Great Lakes. High and mid level clouds will increase and thicken over the western counties in the process. Later this afternoon and early this evening the above system will get close enough to our area to potentially trigger a few scattered showers and thunderstorms across far western New York...with dry VFR weather otherwise prevailing. Our weather will then trend steadily downhill tonight as the center of the aforementioned low makes its way across northern Lower Michigan and pushes its attendant warm front into our region...with this feature making it to about the south shore of Lake Ontario by the end of the TAF period. This will result in a round of fairly widespread showers and scattered thunderstorms making its way across our region from west to east...with flight conditions lowering to lower-end VFR/MVFR across the lower elevations and MVFR/IFR across the higher terrain as the atmosphere moistens. Outlook... Saturday and Sunday...Occasional rounds of showers and scattered thunderstorms with associated reductions to IFR/MVFR...and MVFR/VFR otherwise. Monday...MVFR/IFR ceilings with showers likely and a chance of thunderstorms. Tuesday...Improvement to VFR. && .MARINE... A modest southeasterly to southerly flow will develop today as a warm front approaches the region...however wind speeds should remain less than 15 knots. As the warm front pushes into our region... southeasterlies may then briefly freshen to 15 to 20 knots across central and eastern portions of Lake Ontario later tonight and Saturday morning...however the offshore nature of the flow will direct the bulk of the greater wave action across Canadian waters. Following the warm frontal passage a general south to southwest flow will then prevail over the weekend...though winds should again generally remain below 15 knots. Of greater concern to marine interests will be the potential for scattered thunderstorms with locally higher winds and waves... beginning this afternoon across Lake Erie and western Lake Ontario...then spreading east across the rest of the region over the weekend. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...JJR NEAR TERM...JJR SHORT TERM...Hitchcock LONG TERM...Hitchcock AVIATION...JJR MARINE...JJR