Area Forecast Discussion
Issued by NWS Buffalo, NY
Issued by NWS Buffalo, NY
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386 FXUS61 KBUF 291038 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 638 AM EDT Sat Jun 29 2024 .SYNOPSIS... It will be quite unsettled the first half of the weekend...as a passing warm front this morning will be the first of several boundaries that will generate widespread showers and possibly some gusty...drenching thunderstorms into tonight. Our sub tropical airmass will then give way to less humid conditions in the wake of a cold front on Sunday... although some showers will still be possible...especially east of Rochester. High pressure will then guarantee PERFECT weather for outdoor activities Monday and Tuesday. && .NEAR TERM /THROUGH SUNDAY/... ...Torrential Downpours and Possibly Severe Weather Today... Unfortunately...today will not be the nicest day for outdoor activities. A broad storm system over the Upper Great Lakes will push several frontal boundaries through our region during the next 24 hours or so...and this will result in fairly widespread showers and likely some thunderstorms. The latter could include torrential downpours and even isolated strong wind gusts. While there will be several hours of dry time today...it will be difficult to try to time those breaks. Its worth noting that any breaks in the cloud cover today will lead to a notably greater risk for strong to severe thunderstorm activity. The first boundary is a warm front that will push northeast across the region during the course of this morning. A large area of moderate to heavy rain with embedded thunderstorms will accompany this frontal passage. In the wake of the warm front...sub tropical air will flood northwards across our forecast area within the associated warm sector. Tds will surge into the lower 70s with PWAT values swelling to over 2 inches. The latter is more than 2 STD above normal for late June and represent values that are outside of 30 year climatology return intervals. This warm plume of deep moisture will include high freezing levels that will result in warm cloud depths in excess of 13k ft...maximizing the efficiency of rainfall rates within the showers and thunderstorms. This will elevate the risk for torrential downpours...and with short MBE vectors expected...these downpours could be slow moving or even build back to the southwest during their progression. The forcing for the increasingly widespread showers and likely thunderstorms today will be a pre-frontal trough that will trudge through the area several hours behind the aforementioned warm front. All of this has led to a slight risk for excessive rainfall... especially across the western Southern Tier and Eastern Lake Ontario region where CAMs and high-res guidance is favoring the most widespread convection. Its worth noting that flash flood guidance suggests that it would take roughly 1.5 to 2 inches of rain in an hour to induce localized flooding concerns. A Marginal Risk of excessive rainfall will be found elsewhere. In regards to the risk of severe weather today...it will largely come down to how much diurnally induced instability we can achieve. While a few hundred joules/kg will be in the environment already...any breaks in the cloud cover will potentially allow as much as 1000 j/kg of SBCAPE to build. Meanwhile...a 40-45kt low level jet will offer PLENTY of shear for any true convection to become better organized. 6km bulk shear values of 40kts or better will include 0-1km SRH that will exceed 200 m2/s2...favoring the development of supercells...both in advance of any line segments or within the convective clusters themselves. Given poor lapse rates though...this threat will heavily depend on added diurnal instability. The greatest chance for this will be across the western Southern Tier...and especially SOUTH of the border...with the highest risk of severe weather coming in the form of damaging straight line winds along with isolated tornadoes. Large hail is NOT anticipated given the poor lapse rates and likely lack of SIGNIFICANT instability. The pre frontal sfc trough and deep plume of sub tropical moisture will push east of our forecast area early tonight. While there can still be some torrential downpours east of Lake Ontario early...the showers will taper off from west to east within the shrinking column of moisture. It will remain rather mild and somewhat humid though with the airmass yet to change ahead of a cold front. While Sunday will prove to be a nicer day...the passage of the initial cold front during the morning may provide a short lived uptick in shower coverage. The most widespread showers will remain east of Lake Ontario. Otherwise...it will be quite breezy in the wake of the aforementioned cold front with increasingly comfortable conditions due to the tumbling Td`s. Interestingly...our high temperatures in the low to mid 70s will occur by midday/early afternoon with slowly falling mercury readings thereafter. This is unusual for this time of year... so this gives you a semblance of how strong the cold advection will be in the wake of the first cold front. && .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY NIGHT/... Sunday night the core of the upper level trough and secondary cold front will slide south across our region. Coupled with upsloping and lake influences (the latter owing to rather cool 850 mb temps falling to around +5C to +6C)..the above should generate a fair amount of cloud cover along with some scattered showers...with the greatest pcpn potential lying east and southeast of Lake Ontario. With this in mind have increased both PoPs and cloud cover notably from blended guidance...which appears to be handling these rather poorly. Otherwise it will be a much more comfortable night for sleeping...with lows ranging from around 50 across the interior Southern Tier and North Country to the mid 50s across the lake plains. Sprawling Canadian high pressure and plentiful dry air will then slowly meander its way from the Upper Great Lakes to the mid- Atlantic coastline Monday and Tuesday...while low-amplitude upper level ridging builds across the region aloft. This will provide us with fine weather to start off July...with highs in the upper 60s to lower 70s Monday warming to the upper 70s and lower 80s on Tuesday as a southerly return flow of warmer air develops around the backside of the departing ridge. In between...ideal conditions for radiational cooling will allow Monday night`s lows to range from the mid-upper 40s across the interior of the Southern Tier/North Country to the lower to mid 50s elsewhere. Humidity levels will also remain comfortable throughout...with surface dewpoints only inching up into the 55-60 range by later Tuesday. Tuesday night the surface ridge will slip a little further offshore...while the next mid/upper level trough and surface low pivots across Manitoba and Ontario Provinces. With our region firmly embedded within the deepening/strengthening southerly flow in between these two systems...it will be a much warmer night than the preceding two...with readings generally ranging through the 60s. Meanwhile humidity levels will remain tolerable...as surface Td`s will linger in the 55-60 range. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... Wednesday and Thursday the aforementioned trough and surface low will continue to make its way eastward to Labrador...and in the process will ease a weak trailing cool front across our area Wednesday night and early Thursday. Out ahead of this boundary heat will build on Wednesday...with 850 mb temps surging into the upper teens...thereby supporting highs climbing back to the mid 80s to lower 90s in most areas. Humidity levels will also be on the increase...with surface dewpoints climbing into the mid-upper 60s and lending a decidedly muggy feel to the afternoon. As the cool front impinges upon this sultry airmass later Wednesday afternoon and especially Wednesday evening...it should help to set off at least some scattered convection...which could prove problematic for any holiday fireworks displays scheduled for Wednesday evening. Convection should then tend to diminish in coverage from northwest to southeast later Wednesday night and Thursday as the passing cool front slips off to our south and ushers in a slightly cooler and less humid airmass...though cannot rule out some spottier showers and storms lingering into Thursday afternoon near the NY/PA border. Otherwise slightly cooler highs in the lower to mid 80s are expected for Independence Day...though humidity levels will likely remain elevated. The weak cool front then looks to stall out not far to our south Thursday night and Friday...as a weak wave of low pressure develops and ripples eastward along the boundary. While the medium range guidance packages unsurprisingly exhibit differences on the timing and strength of this wave...a rough consensus would currently suggest a largely dry evening on July 4th...followed by a renewed potential for scattered showers and storms later Thursday night into Friday...with the latter greatest near the Pennsylvania border. This being said it`s pretty early...with changes to this overall scenario certainly possible over the coming days. Otherwise...it will likely remain warm and on the humid side through the end of the week. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... A warm front pressing to the northeast through the forecast area this morning will prompt VFR conditions to rapidly deteriorate to MVFR levels. The front will be preceded by a large area of moderate to heavy and possibly some thunderstorms. MVFR to IFR conditions can then be expected regionwide by this afternoon. A pre frontal trough pushing across the state will prompt widespread showers and possible strong thunderstorms within a very soupy sub tropical airmass. While the heavy showers and thunderstorms will taper off from west to east late this afternoon and night...MVFR to IFR cigs can be expected. Outlook... Sunday...VFR/MVFR with scattered showers. Monday and Tuesday...VFR. Wednesday...Mainly VFR. && .MARINE... It will be quite unsettled today...as a broad storm system centered north of the SOO will push several frontal boundaries across the Lower Great Lakes. This will result in widespread showers and possibly some gusty thunderstorms. Meanwhile...moderate to fresh southerlies will direct the greatest wave action into Canadian waters. The exception will be the far east end of Lake Ontario where waves will be significant enough to warrant a small craft advisory for sites north of Mexico Bay. Otherwise...expect fairly choppy conditions...especially well offshore. Winds will weaken somewhat tonight while veering to the southwest. This should allow the headline for eastern Lake Ontario to expire. Fresh to strong westerlies can then be expected in the wake of a cold front on Sunday. This will likely lead to a fresh round of headlines for at least the eastern half of Lake Ontario...while choppy conditions will be found elsewhere. Looking further ahead...high pressure drifting across the region Monday and Tuesday will offer fine conditions for recreational boating with generally light winds and negligible waves. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...Small Craft Advisory until 2 AM EDT Sunday for LOZ045. && $$ SYNOPSIS...RSH NEAR TERM...RSH SHORT TERM...JJR LONG TERM...JJR AVIATION...RSH MARINE...RSH