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Area Forecast Discussion
Issued by NWS Buffalo, NY
Issued by NWS Buffalo, NY
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118 FXUS61 KBUF 171824 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 224 PM EDT Sat Aug 17 2024 .SYNOPSIS... A large storm system over the Upper Great Lakes will slowly drift eastward across our forecast area through Monday. This will result in unsettled conditions with occasional showers and a chance of thunderstorms...although there will also be periods of dry weather. Some of the showers could be locally heavy...with a stronger storm or two not also out of the question. Following the passage of this system...Canadian high pressure will build across our region and provide us a prolonged period of fair weather and cooler weather that will last for most of next week. && .NEAR TERM /THROUGH TONIGHT/... Broad and vertically stacked low pressure will slowly drift east across Lower Michigan today and across southern Ontario province tonight. The cyclonic flow aloft associated with this trough and embedded disturbances will bring an unsettled pattern which will last through the period. This afternoon, a warm front exited to the east of the area, and a brief period of subsidence behind this allowed for some sunshine which increased instability. LAPS shows SB CAPE 1000 to 2000 J/Kg across Western New York, which will support increasing areal coverage of storms this afternoon into early evening. Limited agreement among mesoscale guidance that the steadiest storms will develop along a weak boundary across far Western NY this afternoon and then will gradually move eastward across the Genesee Valley before weakening late this evening. However, scattered showers and thunderstorms cannot be ruled out anywhere during this time. Wind profiles are modest from a severe weather perspective, with only about 25 to 30 knots at 850mb and 700 mb winds not much stronger. As a result there`s limited wind shear, but a few strong to severe pulse storm cannot be ruled out, especially considering the large scale lift provided by the shortwave. PWAT values of 1.75 to 2 inches across Western NY also support locally heavy rainfall, with a risk for flash flooding from training or slow moving storms. This will have to be monitored, especially through this evening. After this, showers and storms will taper off some late tonight as instability wanes, but at least a chance will persist during the entire overnight period. Lows will range from the mid 60s to around 70, with a risk of fog across higher terrain in the Southern Tier late in the night. && .SHORT TERM /SUNDAY THROUGH TUESDAY NIGHT/... Unsettled weather will continue into the start of the work week, with a cold front crossing the region from west to east early Monday. We will hang onto showers and a few thunderstorms through the day with still deep moisture, anabatic frontal precipitation, and convergence along a 25 knot northerly LLJ ahead of the axis of the mid level trough. These showers will end through the evening hours towards the east, with some clearing towards the west. This northerly flow and steepening low level lapse rates will encourage cloud reformation Tuesday, with partly to mostly cloudy skies over the region...until a much drier airmass from the north diminishes the strato-cu later through the day. Clearing skies, light winds and mid single digit 850 hPa temperatures will quickly drop temperatures in the evening...with overnight lows Tuesday night dropping into the low to mid 40s inland to mid 50s along the lake shorelines. Highs Monday and Tuesday will largely remain in the 60s under cloud cover and within an 850 hPa airmass that will be in the mid single digits Celsius. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... Sprawling surface high pressure will cross the region early this period, with cool low humid conditions Wednesday through Thursday morning giving way to day-to-day warming behind the surface high through Saturday. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... Approaching mid level trough and diurnal instability will support increasing coverage of showers and thunderstorms this afternoon into this evening. Greatest coverage will push into far Western NY through 20Z then spread east to the Genesee River and KROC late afternoon and evening before weakening. Thunderstorms driven by subtle features, making exact timing challenging so handled with tempo groups for most TAF sites. Mainly VFR flight conditions outside of brief MVFR or lower due to vsby in heavier rain. Showers and thunderstorms taper off some after midnight, but there still will remain a risk throughout the overnight hours. Increasing low moisture with the approach of the trough will result in expanding MVFR cigs with most sites MVFR by Sunday morning. Chances for showers and thunderstorms will again increase Sunday afternoon, but low confidence in exact timing and location. Outlook... Sunday night...VFR/MVFR lowering to mainly IFR following the wind shift. Showers and scattered thunderstorms with lowering cigs with the northwesterly wind shift. Monday...MVFR/IFR ceilings with showers likely and a chance of thunderstorms. Tuesday...Improvement to VFR. Wednesday and Thursday...VFR. && .MARINE... Over the weekend expect a general southerly to southwesterly flow on Lake Erie and a southerly to southeasterly flow on Lake Ontario... with winds generally remaining at or below 15 knots. The above said...there will be a period of slightly stronger (15-20 knot) SSE flow on eastern Lake Ontario later tonight and early Sunday. Fortunately...the offshore component of the flow will direct the bulk of the greater wave action across Canadian waters and should preclude the need for any Small Craft Advisories during these time periods. Of greater concern to marine interests this weekend will be the potential for scattered thunderstorms...with locally higher winds and waves possible in and near any such storms. Following the passage of a cold front...northerly flow will develop later Sunday night...then will strengthen across the Lower Great Lakes Monday. This will at least bring some choppy conditions to Lake Erie...with somewhat stronger winds across Lake Ontario potentially leading to some advisory-level conditions along the south shore of that lake Sunday night through Monday night. Conditions should then gradually improve on Tuesday as Canadian high pressure begins building into the region...with a slackening pressure gradient allowing for winds and waves to subside. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...JJR NEAR TERM...Apffel/JJR SHORT TERM...Thomas LONG TERM...Thomas AVIATION...Apffel/JJR MARINE...Apffel/JJR