178 FXUS61 KBUF 090906 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 506 AM EDT Sun Aug 9 2020 .SYNOPSIS... An area of high pressure over the Ohio Valley today will drift to the Eastern Seaboard by Monday. This will provide mainly dry conditions through the start of the new work week, although a few weak upper level disturbances crossing the region may bring a few showers from time to time, especially across northern areas. A weak cold front will then cross the region on Tuesday, bringing the next chance for more widespread showers and thunderstorms. Otherwise, temperatures will remain above normal through the upcoming week. && .NEAR TERM /THROUGH TONIGHT/... The typical valley fog across the Southern Tier will lift out by mid morning. An area of surface high pressure will reside across the Ohio Valley today, providing the bulk of the area with dry weather. However, an upper level trough moving down the Ottawa Valley this morning, will cross northern NY this afternoon. This will keep the bulk of the scattered showers and storms associated with this feature to the north of Lakes Erie and Ontario across southern Ontario Province. However, as upper level energy moves across northern NY this afternoon, there will be the chance for a few showers and storms for areas east of Lake Ontario into the Saint Lawrence Valley during the second half of the day. Southwest winds will increase with the approach of the trough, with gusts of 20-30 mph northeast of Lakes Erie and Ontario in the afternoon as the surface pressure gradient tightens and somewhat stronger winds off the deck mix down to the surface. Otherwise, temperatures will nudge upward another degree or two today, with highs in the lower to mid 80s across the majority of the area. A few showers/isolated storms may linger east of Lake Ontario through late this evening as the upper level trough exits east of the area. The next weak shortwave will cross the area during the second half of the night, renewing the chance for a few more showers and storms from the Niagara Frontier east and northeast to the eastern Lake ontario region as this feature interacts with a subtle weak warm front lingering from central Lake Ontario into Central NY. With little in the way of precip, or even cloud cover for that matter across the Southern Tier, may see another night with typical valley fog. Low temperatures tonight will be much warmer than previous nights, as readings will likely only fall back into the mid and upper 60s across the bulk of the area, with lower 60s found across the higher terrain. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... A subtle warm frontal boundary will be draped over and southeast of Lake Ontario Monday morning, with a convectively augmented mid level shortwave also moving southeast across the area. Weak moisture convergence near the warm front and forcing from the shortwave may support a few scattered showers and storms Monday morning over and southeast of Lake Ontario, with this activity then drifting east during the afternoon. A few more isolated showers and storms may develop along and inland of the lake breeze boundaries Monday afternoon, but the majority of the area will stay dry. Temperatures will continue their day to day rise, with highs in the upper 80s to around 90 at lower elevations away from lake influences. Dewpoints will also climb into the upper 60s to around 70. This will translate into a heat index in the 90-95F range. The most probable location of marginal heat advisory criteria (95F) is from the Genesee Valley eastward through the western Finger Lakes to Oswego County. Any isolated diurnal showers and storms will dissipate Monday evening, leaving dry weather overnight. A very warm/muggy airmass and southwest breeze will not allow temperatures to fall much, with lows in the lower 70s on the lake plains and mid 60s across the interior Southern Tier and Lewis County. Tuesday and Tuesday night a weak mid level trough and associated cold front will approach the area. 00Z model guidance continues to trend slower with this feature, not bringing the cold front through the eastern Great Lakes until very late Tuesday night or Wednesday morning. Tuesday will start dry, with scattered showers and storms developing in the afternoon along lake breeze boundaries and a pre- frontal trough. The scattered showers and storms will continue Tuesday night as the mid level trough and cold front cross the area. PWAT values climb to around 1.75 inches, so any storms will be capable of very heavy downpours. Relatively weak shear and poor mid level lapse rates will limit the severe weather risk. Tuesday will be another very warm and humid day, with highs in the mid 80s across Western NY and around 90 from the Genesee Valley eastward at lower elevations. The heat index may again reach 95 from the Genesee Valley to the western Finger Lakes and Oswego County. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... The cold front moving through the area late Tuesday night and Wednesday morning will lay out in an east-west orientation from the Ohio Valley to PA Wednesday, and stall in place through the end of the week. Several weak, convectively augmented waves will move eastward along the front, providing periods of enhanced ascent and moisture convergence. If a stronger frontal wave materializes it may also modulate the frontal position. The GFS/GEFS mean remains on the northern side of the guidance envelope, with the ECMWF/GEM keeping the front and associated sensible weather well south of the area. Given the emerging ECMWF/GEM consensus of a farther south solution, lowered POPS Wednesday through Friday with a dry forecast for the majority of the area and low chance POPS over the Southern Tier. By Saturday deeper moisture, instability, and forcing may begin to creep back northward as the next trough moves into the Upper Midwest, bringing a chance of a few scattered showers and storms. Temperatures will continue to run above average Wednesday through next weekend despite being to the north of the stalled frontal zone. Expect highs in the mid 80s at lower elevations each day, with lows in the 60s. Dewpoints will remain somewhat lower to the north of the boundary, keeping humidity relatively comfortable. && .AVIATION /09Z SUNDAY THROUGH THURSDAY/... Typical river valley fog will impact the Southern Tier through mid morning with local IFR conditions. Mid and upper level clouds will be found across the area today, with some low VFR decks east of Lake Ontario during the second half of the day, where a few showers and storms will be possible as well this afternoon/evening. Otherwise, it will be mainly dry with VFR flight conditions area wide through this evening. Outlook... Sunday night through Monday...Mainly VFR. A small chance of showers. Tuesday...Showers and thunderstorms likely. Brief MVFR/IFR possible. Wednesday and Thursday...Mainly VFR with an afternoon/evening shower or thunderstorm possible. && .MARINE... A tightening pressure gradient will allow southwest winds to increase on both lakes today ahead of a weak upper level trough. This will produce choppy conditions on Lake Erie. Winds will be a bit lighter on Lake Ontario, but still enough to generate some chop, especially across the western half of the lake. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...JM NEAR TERM...JM SHORT TERM...Hitchcock LONG TERM...Hitchcock AVIATION...JM MARINE...JM