911 FXUS61 KBUF 212009 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 409 PM EDT Sat Aug 21 2021 .SYNOPSIS... A warm and humid airmass will remain in place for the rest of the weekend, allowing for a few scattered showers and thunderstorms mainly during the afternoon and early evening today and again Sunday. Heat and humidity will continue through the middle of next week, along with the chance of a few spotty showers and thunderstorms. && .NEAR TERM /THROUGH SUNDAY/... Radar imagery showing a few diminishing showers over the Niagara Frontier and western Lake Ontario, with developing heavier showers east of Lake Ontario and across Central NY. A weak mid level closed low over West Virginia and southwest PA this afternoon will drift east into the Mid Atlantic through Sunday, with a weak inverted trough in the mid levels extending northward into the eastern Great Lakes. Weak vorticity maxima will continue to drift north and west across our region in response to flow around this weak mid level low, and a feed of Atlantic moisture will also continue. Given how weak the forcing is, most of the showers and thunderstorms through the rest of the weekend will be closely tied to the diurnal cycle, with peak coverage during the afternoon today and Sunday. Hurricane Henri will also move northward to the east of this system, but have no direct impact on our area. This afternoon and early evening expect showers and a few thunderstorms to continue to develop as diurnal heating peaks, with the best coverage across the eastern Lake Ontario region and the western Finger Lakes where the deepest moisture resides and forcing ahead of a weak vorticity maxima provides an added boost. Coverage of rain will be more sparse across far Western NY near Lake Erie, but a few showers are still possible here as well. The showers and storms will taper off by mid evening as the boundary layer stabilizes. Plenty of low/mid level moisture will remain in place overnight with partly to mostly cloudy skies. Despite the cloud cover, abundant low level moisture and weak surface winds will allow for patchy fog to develop. The most widespread fog will be across the valleys of the Southern Tier and western Finger Lakes. The fog will dissipate by mid morning Sunday. The abundant low level moisture will combine with diurnal heating to support scattered showers and thunderstorms in the afternoon, mainly across the higher terrain inland from Lakes Erie and Ontario. Developing north/northwest flow will allow stable lake shadows to spread inland across the lake plains in the afternoon, decreasing the chance of rain close to the lakes. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... Sunday night tropical system Henri will slowly meander its way north-northwestward along the New York-southern New England border... while becoming increasingly absorbed by the deep-layer closed low over the mid-Atlantic states. On this track the heavy rains directly associated with Henri will remain safely confined to our southeast... though the larger-scale trough and tropical airmass across our region will still lead to the potential for some scattered showers and isolated thunderstorms across eastern/southeastern portions of the area. On Monday the closed low will open up a bit and slowly lift north- northeastward across western New England. In doing so...this will keep Henri and any of its direct impacts again confined well to our east...though daytime heating of our warm and soupy airmass should again lead to the development of some diurnally-driven showers and thunderstorms across our area. The potential for these will be highest across the North Country and interior portions of the Finger Lakes where support from the larger-scale trough and diurnal instability will respectively be the greatest...with chances notably lowering with increasing westward extent across the balance of the area... particularly across the Niagara Frontier where the bulk of the day looks to be dry. At this point the bulk of the activity still looks to be scattered in nature...though a brief period of more numerous showers/storms cannot be ruled out across the North Country/interior Finger Lakes. With the tropical airmass that will be in place...the main issue with any slow-moving storms would be locally heavy rainfall. Monday night any lingering diurnally-driven convection will quickly come to an end with nocturnal stabilization...and as the main mid/ upper level trough ejects northeastward across New England. Once these end...building ridging at all levels will then supply our region with fair and dry weather for the balance of this period. Otherwise...it will remain uncomfortably warm and humid throughout this period. Daytime highs in the low to mid 80s Monday will climb into the mid and upper 80s Tuesday owing to the aforementioned building ridging and attendant warmer temps aloft...while nighttime lows will generally range from the mid 60s to around 70 each night...with readings perhaps a few degrees "cooler" Monday night. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... Humid conditions with near record warmth for some locations as H850T hover near +19C/20C Wednesday ahead of a weak front. Chances for showers and storms will tick up just ahead of this front Wednesday evening, but then diminish a bit as instability wanes Wednesday night. After that, there is still a lot of uncertainty among the various guidance packages for Thursday and beyond. Have kept low end chance POPs for now across most of the forecast area. Could be another round of showers and storms Thursday but it will all depend on the progression of the front. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... Scattered showers and thunderstorms will expand in coverage through mid to late afternoon with the peak of diurnal instability. The best coverage is expected to be east and southeast of Lake Ontario where the best forcing and instability reside. A few of the heavier showers will reduce visibility to MVFR or lower briefly, otherwise VFR will prevail outside the showers through this evening with plenty of diurnal cumulus inland from the Great Lakes. Most of the showers will end by mid to late evening as daytime instability wanes. This will leave partly to mostly cloudy skies overnight. Abundant low level moisture and light winds will allow for patchy fog to develop, with the fog widespread across the valleys of the Southern Tier and western Finger Lakes. Areas of IFR will be found in the fog. Fog will dissipate by mid morning Sunday, with low level moisture evolving into a diurnal cumulus field. The cumulus field will briefly have MVFR bases late morning through midday in some areas before lifting into VFR in the afternoon. Widely scattered showers and thunderstorms will develop again in the afternoon, especially across higher terrain well inland from the lakes. Outlook... Monday...Mainly VFR with the chance of mainly afternoon and early evening spotty showers and thunderstorms. Tuesday...VFR. Wednesday and Thursday...Mainly VFR. A chance of showers and thunderstorms. && .MARINE... Winds will remain light through early next week with negligible wave action. There will be a few scattered showers and thunderstorms each afternoon and evening which may produce locally higher winds in a few locations. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...Hitchcock NEAR TERM...Hitchcock SHORT TERM...JJR LONG TERM...AR AVIATION...Hitchcock MARINE...Hitchcock