386 FXUS61 KBUF 051743 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 143 PM EDT Fri Jul 5 2019 .SYNOPSIS... Very warm and muggy conditions will remain in place through Saturday evening. The humid airmass will fuel more showers and thunderstorms, mainly this afternoon and again on Saturday when a cold front will approach the region. The cold front will cross the area Saturday night with showers ending from north to south. Cooler and much less humid air will move into the area in the wake of the cold front Sunday through early next week. && .NEAR TERM /THROUGH SATURDAY NIGHT/... ...Localized Tropical Downpours Possible Again This Afternoon... Radar and visible satellite imagery showing scattered to numerous showers and storms blossoming along and inland of the lake breeze boundaries. Moderate instability has developed, with temperatures in the mid to upper 80s and dewpoints in the lower 70s contributing to MLCAPE of around 2000J/kg inland from the lakes. New development will continue for the next few hours, with rain coverage peaking during the mid to late afternoon. The main boundary so far is the eastern edge of enhanced SW flow off Lake Erie, with convergence stretching from Chautauqua County to near Rochester. Over time, an approaching weak mid level shortwave should force this convergence zone and associated convection to drift east, carrying the bulk of the showers and storms eastward across the Southern Tier and western Finger Lakes during the mid to late afternoon. Showers and storms will also develop across Central NY, from Ontario County to the Tug Hill region. PWAT values of 1.75-2.00 inches will continue to support torrential downpours with any thunderstorms that develop. There is a little more steering flow than yesterday, with around 15 knots mean in the low/mid levels. This should allow convective cores to remain mobile. The main concern for flash flood potential will be training along boundaries, especially along the slowly propagating lake breeze boundaries this afternoon. This risk will remain very isolated, but if training does develop there may be localized flash flooding given the very moist airmass coupled with favorable tall/skinny CAPE profiles and high freezing levels. Meanwhile stable lake shadows have become well established northeast of Lakes Erie and Ontario. This will keep the Niagara Frontier including Buffalo mainly dry, and also Watertown and the Thousand Islands region. It will be very warm and humid through the rest of the afternoon, with highs in the mid to upper 80s and dewpoints in the lower 70s. This will yield a heat index in the mid 90s across the lower elevations of the lake plains away from the immediate lakeshores. The bulk of the stronger convection will drift east into Central NY and weaken this evening with the loss of daytime heating. A few showers may linger overnight. Late tonight a pre-frontal trough will begin to approach Lake Ontario, and this may bring an increase in shower coverage towards daybreak for areas near and east of Lake Ontario. It will be another warm and very muggy night, with lows in the lower 70s on the lake plains and upper 60s in the Southern Tier and Lewis County. Saturday a pre-frontal trough will slowly cross the eastern Great Lakes from northwest to southeast. The pre-frontal trough, along with any lake breeze and differential heating boundaries will act as a focus for showers and thunderstorms. The increase in large scale forcing from the pre-frontal trough and associated mid level trough should yield the greatest coverage of rain we have seen this week, with even lakeshore areas seeing a high probability of rainfall. PWAT values remain in the 1.75-2.00 inch range, supporting very heavy localized downpours in thunderstorms once again. It will remain very humid Saturday with dewpoints in the lower 70s. The extra clouds and showers will likely keep highs in the lower 80s. The cold front will cross the area from north to south Saturday night. Showers will end with the passage of the cold front. It will remain very muggy in the evening, with drier and cooler air arriving overnight in the wake of the front. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... As we move into the final 24 hours of the weekend...sprawling Canadian high pressure and cooler/drier air will continue building across the Great Lakes and Northeast. This will result in dry weather along with pleasantly cooler and less humid conditions...with leftover cloud cover Sunday morning also giving way to mostly sunny/mainly clear skies. Expect temperatures on Sunday to peak in the mid to upper 70s before falling into the 50s Sunday night...while surface dewpoints settle into the rather comfortable lower to middle 50s. && .LONG TERM /MONDAY THROUGH THURSDAY/... Monday through Tuesday night the center of the Canadian surface high will gradually settle from the Great Lakes to the mid-Atlantic coastline. This will promote continued dry weather and comfortable humidity levels...as the ridge will effectively block the northward return of any Gulf moisture. Meanwhile slow but steady day-to-day airmass modification will result in slowly warming temperatures... with highs climbing back to the lower 80s in many areas by Tuesday. On Wednesday the core of the surface ridge will slide eastward and out to sea...allowing a southwesterly return flow of warmer and somewhat more humid air to spread into our region. This will allow highs to reach into the lower to mid 80s areawide...while surface dewpoints recover into the moderately humid lower 60s. While the increasing warmth and humidity could be enough to support the development of a couple isolated showers and/or storms away from the lakes during the heat of the afternoon...the bulk of the day should be dry. After that...the 00z medium range models diverge markedly on the evolution and track of the next system Wednesday night and Thursday. The GFS and GEM continue to advertise the approach and passage of another mid level trough and cold front with the former notably faster in timing...while the ECMWF is notably further south with the track of the main surface low and actually pushes a more heavily moisture-laden WARM front across our region instead. Either of these scenarios would bring a renewed chance for convection to our region... which for now has been covered in the forecast by increasing broadbrush chance PoPs Wednesday night and Thursday. Otherwise...temps and humidity levels should remain near or slightly above average. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... Scattered to numerous showers and thunderstorms will continue through the rest of the afternoon along and inland of lake breeze boundaries. The best coverage will be from the Southern Tier to the western Finger Lakes to areas southeast of Lake Ontario. VFR will prevail most of the time, but any of the heavy storms will produce brief/local IFR. Tonight...any leftover showers and thunderstorms will come to an end by 03z. This will leave generally VFR weather across the region for the bulk of the night...although an approaching pre-frontal trough will usher in another round of showers and thunderstorms for sites near Lake Ontario after 09z. The pre-frontal trough will slowly cross the area Saturday with numerous showers and thunderstorms. These storms will produce areas of MVFR and brief IFR conditions. Outlook... Sunday through Wednesday...VFR. && .MARINE... A weak surface pressure gradient will remain in place throughout the Lower Great Lakes through tonight. This will keep light winds and negligible waves intact. A pre-frontal trough will then cross the area late tonight and Saturday morning. While winds and waves are forecast to remain below SCA criteria...the frontal passage will generate fairly widespread showers and thunderstorms. The actual cold front will move south across the region Saturday night, with a brief period of moderate northeasterlies developing late Saturday night and Sunday morning. This will likely produce a brief period of Small Craft Advisory conditions along the south shore of Lake Ontario, peaking early Sunday morning. Winds and waves will diminish Sunday afternoon and remain low through early next week as high pressure builds into the Great Lakes region. && .TIDES/COASTAL FLOODING... Northeasterly winds will increase in the wake of a cold front over Lake Ontario late Saturday night and Sunday morning. The period of stronger winds (around 20 knots) will be brief, but will likely be enough to generate a few hours of 3-5 foot waves along the south shore of the lake. Many of the most susceptible areas to lakeshore flooding (such as Sodus Bay and the numerous bays and inlets in Monroe County) are most exposed to wind and waves from the northeast. With this in mind, we have issued a Lakeshore Flood Watch along the south shore of Lake Ontario from Niagara to Wayne counties for late Saturday night through early Sunday afternoon. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Heat Advisory until 6 PM EDT this evening for NYZ001>005-011- 013. Lakeshore Flood Watch from late Saturday night through Sunday afternoon for NYZ001>004. MARINE...None. && $$ SYNOPSIS...Hitchcock NEAR TERM...Hitchcock SHORT TERM...Hitchcock/JJR LONG TERM...JJR AVIATION...Hitchcock MARINE...Hitchcock/RSH TIDES/COASTAL FLOODING...Hitchcock