Area Forecast Discussion
Issued by NWS Buffalo, NY
Issued by NWS Buffalo, NY
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348 FXUS61 KBUF 052041 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 441 PM EDT Wed Jun 5 2024 .SYNOPSIS... A slow moving cold front will press through the region later tonight and Thursday...and while this will lead to increasingly widespread showers and possibly some drenching thunderstorms...it will also bring an end to our stretch of summery weather. In fact... temperatures are slated to average below normal from Friday through Monday of next week. The cooler weather will be accompanied by fairly frequent shower activity. && .NEAR TERM /THROUGH THURSDAY NIGHT/... It will be warm and humid across the region late this afternoon...as a deepening southerly flow ahead of an approaching cold front will allow a sub tropical airmass to move in from the Ohio valley. A few showers and thunderstorms have developed in the warm and moist air mass through late afternoon. Most of this activity is in the vcnty of an elevated warm front, although there are a few storms out ahead of it east of Lake Ontario. The environment is unstable to the tune of 1500-2000 j/kg of SBCAPE...so its only a matter of having any weak boundaries from the aforementioned area of showers being able to initiate the convection. DCAPE values in the vcnty of 1000 j/kg would then promote the risk for gusty storms for those areas. Otherwise...locally heavy rain would be the only real concern. The deep plume of sub tropical moisture will be situated over our region tonight...while a cold front will SLOWLY move through. There will be a short break between the afternoon instability showers and storms and the storms just ahead of the cold front. This should reach far western NY around 11 p.m. this evening. This timing is a little slower than previous forecasts. This will also pose a risk for `heavy rainers` and localized gusty winds with some of the storms. As we move through the wee hours of the morning towards daybreak... the most concentrated areas of showers and possible thunderstorms will make their way to the Eastern Lake Ontario region. The risk for gusty winds with the convection should drop off by this point. Otherwise...tonight will be a warm and muggy night with mins in the more populated regions not falling below 65. Thursday...the slow moving cold front will make its way across the Eastern Lake Ontario during the morning hours. This will continue to support cat pops for that area along with the potential for locally heavy rain. The scenario will be far more convoluted over the western counties. While a negatively tilted mid level trough will continue to dig over the Lower Great Lakes on Thursday...weak sfc based ridging will develop over the western counties. This combination will work against organized shower activity...except within a pronounced area of low level convergence that will become established from KIAG past KROC...basically just north of the NYS Thruway. Showers will be likely in this particular corridor. For the immediate BUF area to near KGVQ...a lake shadow is expected with gusts to near 30 mph. The real airmass change though will take place Thursday night in the wake of a secondary cold frontal passage. This will bring a temporary end to the scattered shower activity...as Tds will drop into the 50s. Towards daybreak though...deeper moisture on the backside of a deep mid level low in the vcnty of the SOO will start to circulate across the Lower Great Lakes. Lift underneath the front left exit region of an 80-90kt H25 jet should be enough to restart at least scattered shower activity over the far western counties... and particularly across Chautauqua county and srn Erie co. && .SHORT TERM /FRIDAY THROUGH SUNDAY/... Opening the period Friday, deep troughing will be found across much of southern Canada and the Great Lakes. Two broad yet distinct areas of anticyclonic flow aloft will initially be embedded within this trough: one over central MB/SK, and the other down across southern ON and the Great Lakes. Through the course of the weekend the latter will come to dominate the longwave pattern across much of the eastern CONUS, with a single large closed low aloft gradually sliding east to New England through the end of the weekend. This pattern and its evolution will keep the core of the upper level jet stream mainly to our south, allowing a continuous flow of cool, moist Canadian air into the region while also periodically placing the forecast area under regions of upper level divergence. In terms of sensible weather, this will translate to a rather unsettled pattern Friday right through the weekend with temperatures averaging below normal. While the nature of the convection will be a bit different each day...Chances/coverage of showers and thunderstorms will generally follow the diurnal insulation curve and be maximized during peak heating in the afternoon hours, especially inland from the lakes. Friday in particular will feature rather widespread shower activity as robust shortwave energy pivots through the eastern Great Lakes. Conversely, shower coverage should become increasingly scattered through the evening hours with the loss of daytime heating, though periodic upper level jet divergence and quick hitting shortwave troughs will maintain Chc PoPs overnight and through the morning hours. In fact, with 850H temps expected to bottom out around +4C and recent lake temperature measurements in Buffalo and Rochester between 61-63F...Not totally out of the question we see some weak lake enhanced rain at times, especially Friday night. Though, 850H temps are very marginal and the water temperatures over the open waters of the lakes are likely much cooler. All this being said, while the expected showers and occasional thunderstorms will certainly be a nuisance for those looking to plan outdoor activities, PWATs will likely struggle to become elevated at any given point, staying near or below 1" this period. Combined with limited deep instability (peak MUCAPE values 100-200J/kg), the threat of stronger storms should be limited. For temperatures...Highs Friday through Sunday will average near 5 degrees below normal, only managing to reach the 60s in most areas, perhaps a few low 70s across the interior valleys while the hilltops may only reach the upper 50s. While the airmass will be abnormally cool, a wealth of cloud cover is expected to hold nighttime lows near normal in the low to mid 50s, possibly a few upper 40s across the interior. && .LONG TERM /SUNDAY NIGHT THROUGH WEDNESDAY/... Eastern CONUS trough pattern will persist through the first part of the period, with the bulk of the unsettled weather Sunday night into the start of the new work week, before the more highly amplified pattern across the CONUS starts to relax a bit. This will also be reflected in our temperatures as readings still below normal on Monday, modify back to near normal levels for Tuesday and Wednesday. The catalyst for this modest change in the overall pattern will be a robust shortwave diving south out of Canada through the base of the mean longwave eastern trough, which will actually help to kick the upper trough to our east sometime around the start of the work week. There remains some disagreement in exactly when this feature will pass across western and northcentral NY, thus will cap PoPs at chance for Sunday night and Monday at this point, mainly due to timing differences, as there will likely be a round of showers/isolated storms along and ahead of the trough axis as it passes through. PWATs at or below climatological means along with decent movement, so not too concerned with any hydro issues at this time. As alluded to above, our airmass will start to modify for the second half of the period as the overall upper level pattern somewhat deamplifies across the CONUS. In fact, latest guidance continues to trend drier for Tuesday and Wednesday with weak high pressure surface and aloft building in over the region. && .AVIATION /21Z WEDNESDAY THROUGH MONDAY/... Scattered showers and thunderstorms through 03Z may briefly impact TAF sites. Mainly VFR outside of this activity. As a cold front approaches and moves through tonight...more widespread showers can be expected...along with some gusty thunderstorms. The onset of the more widespread pcpn will include a change to MVFR Cigs. IFR conditions will set up across the Srn Tier. MVFR to IFR cigs Thursday morning will then gradually give way to VFR weather. The most widespread showers and possible thunderstorms will be east of Lake Ontario through 15z. Outlook... Thursday night...Mainly VFR weather. Friday through Monday...VFR/MVFR with mainly daytime showers likely with possible thunderstorms. && .MARINE... A southerly flow will strengthen today into tonight ahead of a slow moving cold front approaching from the west. With the flow being mainly offshore, the main impact will just be a bit of an uptick in light chop toward the open waters. The cold front will cross the lower Great Lakes late tonight and Thursday morning, however expect a threat for thunderstorms this afternoon through Thursday. SW to WSW winds will freshen on both Lakes Thursday and Friday in the wake of the cold frontal passage with choppy waters developing. Conditions may possibly near Small Craft Advisory criteria for a couple of brief periods Thursday and Friday afternoon, especially across eastern Lake Erie. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...RSH NEAR TERM...Apffel/RSH SHORT TERM...PP LONG TERM...JM AVIATION...Apffel/RSH MARINE...JM/TMA