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Area Forecast Discussion
Issued by NWS Buffalo, NY
Issued by NWS Buffalo, NY
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328 FXUS61 KBUF 151841 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 241 PM EDT Mon Jul 15 2024 .SYNOPSIS... An area of thunderstorms will move across the area this afternoon and evening, bringing a risk of damaging winds, hail, and heavy rain. An unsettled pattern will then continue through midweek...with another round of strong thunderstorms possible Tuesday. A cold front will sweep across the area midweek...with high pressure building across our area in its wake and providing mainly dry...cooler...and much less humid conditions for the second half of the week. && .NEAR TERM /THROUGH TUESDAY/... ...RISK FOR SEVERE THUNDERSTORMS WITH DAMAGING WINDS AND HEAVY DOWNPOURS THIS AFTERNOON AND EVENING...AND AGAIN ON TUESDAY... Severe Thunderstorm Watch 538 remains in effect until 7 pm this evening for all of western and north central New York...as well as the adjoining waters of Lake Erie...Lake Ontario...and the Niagara River. Satellite imagery shows an MCV over nearby Southern Ontario, with this forecast to track across Lake Ontario this afternoon and evening. MCVs are commonly linked to severe weather in our area since they increase wind shear to the south of its track. In this case, timing is diurnally favorable. On its eastern flank...a broken line of strong to severe convection continues to develop across extreme far western New York and eastern Lake Erie...and this should continue to develop and sweep across the area from west to east this afternoon and evening...with the timing of the greatest risk for severe weather roughly through 5 pm across far western New York...between 3 and 7 pm for the Genesee Valley and Finger Lakes (Rochester)...and from 4 to 8 pm east of Lake Ontario (Watertown). While there is not as much wind shear as last week (July 10th) when there were multiple tornadoes in the forecast area, there is still ample enough shear to support damaging straight line winds. However, this should not be downplayed, since damaging winds typically impact a larger area and can still cause significant damage. The risk for tornadoes is non-zero, but for most areas straight line wind gusts will be the main concern along with a secondary potential for large hail...of which we`ve already had a few reports with an initial storm that lifted across the Niagara Frontier a bit earlier. With PWATs up around 1.75 inches, any storms could also produce torrential downpours, although the localized flash flooding risk is a lesser threat as this activity will be moving along fairly quickly. Otherwise, it will remain very warm and humid this afternoon with highs mainly in the mid to upper 80s and dew points in the upper 60s to lower 70s. With the expected convection...apparent temperatures should remain below Heat Advisory criteria across the Genesee Valley and northern Finger Lakes this afternoon. The MCV will slide east of our region this evening...with associated showers and storms quickly winding down from west to east in its wake. Can`t rule out a few additional scattered showers or an isolated storm overnight given the very warm and moist airmass, however expect the bulk of the area to be largely dry following the departure of today`s MCV. It will be another sultry night with lows in the upper 60s to low 70s. During Tuesday the longwave upper-level trough will remain well upstream of the area over northwest Ontario. A weak low level trough axis will linger in place from the Ohio Valley to New England, with its position modulated by numerous rounds of convection and associated composite outflow. This feature will serve as the conduit for yet another convectively generated vorticity maxima/MCV that will move east across our region Tuesday, with this feature supporting another round of showers and thunderstorms that will cross the area from west to east. The 12z/15 suite of model guidance still suggests an earlier arrival of this next wave compared to today`s...though this is just a little bit slower than seen in last night`s guidance. Current timing takes this feature across western NY between the morning/midday hours, then the eastern Lake Ontario region/central New York early Tuesday afternoon. The earlier arrival of forcing, clouds, and showers relative to the diurnal cycle may act to limit potential instability across far western New York...with areas further south and east having a better opportunity for notable diurnal destabilization. Deep layer shear is not particularly strong (only around 30 knots) across western New York...however this looks to be greater with increasing northeastward extent - with this especially the case across the North Country where 0-6km bulk shear is currently projected to be in the 40 to 50 knot range. As is typically the case...the MCV will also likely bring a mesoscale region of enhanced low/mid level shear, convergence, and ascent as it crosses the region...thereby providing a more favorable environment for strong to severe storms. At this point strong damaging winds again appear likely to be the primary severe weather threat...along with a secondary risk for large hail. Additionally...the enhanced shear supplied by the MCV will also support a low but nonzero risk for an isolated tornado or two...with this risk likely greatest across the eastern Finger Lakes and North Country where the environmental shear currently looks to be highest. In the wake of the MCV, a few more showers and thunderstorms may develop along lake breeze driven convergence zones in the afternoon and evening, mainly from the Southern Tier through the Finger Lakes and Central NY. Increasing southwest flow off Lake Erie will likely produce a stable lake shadow northeast of the lake with mainly dry weather following the morning/midday convection. Otherwise it will be very warm and humid again Tuesday, with highs in the low 80s for Western NY and mid to upper 80s from the Genesee Valley into Central NY. While apparent temperatures could briefly tickle 95F from the Genesee Valley into Central NY, the brief/ marginal nature of these and the potential for clouds and convection to keep temperatures a few degrees lower both preclude the need for any Heat Advisories at this time. && .SHORT TERM /TUESDAY NIGHT THROUGH THURSDAY NIGHT/... Tuesday night through Wednesday night the longwave trough will gradually dig through the Great Lakes, ending up in Quebec by Thursday morning. One or more convectively augmented shortwaves may cross NY/PA Tuesday night through Wednesday, supporting ongoing chances of a few showers and thunderstorms at times. The cold front will cross the region later Wednesday afternoon, with the chance of showers and thunderstorms then ending from northwest to southeast late Wednesday through Wednesday night. Drier and less humid air will arrive later Wednesday night in the wake of the cold front. A period of much drier, less humid, and somewhat cooler weather will arrive Thursday and likely last through the long term period (more on which follows below). High pressure will build in Thursday and Thursday night...with an attendant pool of cooler air leading to highs in the 70s Thursday...and lows ranging through the 50s Thursday night. && .LONG TERM /FRIDAY THROUGH MONDAY/... It`s looking like this will be a stretch of spectacular weather across the region, with a broad ridge of high pressure building across the region. A weak cold front will drop southward across the region Sunday, but its passage should largely be rain-free with possibly an isolated shower. Otherwise, there`s good model agreement providing high confidence in rain-free weather. Temperatures will be near normal with daytime highs averaging in the mid 70s to lower 80s and nighttime lows mainly in the mid 50s to lower 60s. && .AVIATION /19Z MONDAY THROUGH SATURDAY/... A convectively augmented shortwave will push across the region this afternoon and evening along with a round of showers and strong to severe thunderstorms. The primary severe weather threat will be strong wind gusts to 50 knots...with a secondary risk for large hail. Expect brief periods of MVFR/IFR in heavier showers and storms, with mainly marginal MVFR to low VFR CIGS otherwise. This wave will push east of the area between late this afternoon and early this evening...followed by a return to mainly VFR conditions for the rest of the night. This being said...there could be a brief period of lingering MVFR ceilings behind this wave...with additional MVFR/IFR ceilings also possible across the Southern Tier late tonight. On Tuesday yet another convectively-driven wave will cross the area from west to east during the morning and early afternoon hours. This will support another round of showers and thunderstorms...with some of the storms again potentially strong to severe...with this risk greatest from the Finger Lakes eastward across the North Country. As is the case today...strong wind gusts to 50 knots and large hail will be the main severe weather threats. Otherwise brief periods of MVFR/IFR will again be possible within any stronger/heavier showers and storms. In the wake of this second wave...a few more showers and storms and localized MVFR restrictions may develop along lake breeze driven convergence zones Tuesday afternoon and evening, mainly from the Southern Tier through the Finger Lakes and Central NY. Meanwhile conditions should tend to return to VFR further to the north and west. Outlook... Tuesday night...VFR/MVFR with scattered to numerous showers and thunderstorms. Wednesday...VFR/MVFR with a chance of showers and thunderstorms. Thursday through Saturday...VFR. && .MARINE... A passing disturbance will bring widespread showers and thunderstorms this afternoon and evening...with some storms capable of generating strong wind gusts and locally higher waves on both Lakes Erie and Ontario. In the wake of this disturbance southwest winds will increase...resulting in a brief period of small craft conditions on Lake Erie this afternoon and evening. Southwest flow will increase again late tonight through Tuesday, producing more notable chop on both lakes, with a period of Small Craft Advisory conditions appearing increasingly likely on Lake Erie Tuesday following the passage of yet another disturbance. This second disturbance will also likely generate a another round of showers and storms across our region...with any stronger storms again capable of strong wind gusts and locally higher waves. Periodic chances for showers and thunderstorms will then continue across eastern Lake Erie and Lake Ontario through Wednesday, with the potential for locally higher winds and waves in and near any storms. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...Small Craft Advisory until 11 PM EDT this evening for LEZ040- 041. && $$ SYNOPSIS...JM/JJR NEAR TERM...Apffel/Hitchcock/JM/JJR SHORT TERM...Hitchcock/JJR LONG TERM...Apffel AVIATION...JM/JJR MARINE...JM/JJR