Area Forecast Discussion
Issued by NWS Buffalo, NY

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911 FXUS61 KBUF 280744 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 344 AM EDT Fri Jun 28 2024 .SYNOPSIS... Beautiful weather will be in place today...as high pressure overhead in the morning will drift off the coast of Long Island by this evening. Conditions will then deteriorate tonight and particularly on Saturday...as low pressure crossing the Upper Great Lakes will push several frontal boundaries through the region. Scattered showers late tonight will become much more numerous on Saturday when a sub tropical airmass will support some heavy rain as well. Not a good day at all for outdoor activities. Sunday will offer some improvement...but a few showers will still be possible. && .NEAR TERM /THROUGH SATURDAY/...
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...Severe Weather Threat and Torrential Downpours on Saturday... High pressure overhead early this morning will gradually make its way to the east during the course of the day...eventually moving off Long Island by this evening. While some cirrus will stream across the far western counties today and actually thicken somewhat during the afternoon...beautiful weather can anticipated to end the work week. It will be comfortable with continued low humidity...but warmer by some 5 to 10 degrees...as afternoon temperatures will reach 75 to 80. The higher end of that range will be near Lake Erie and in the downslope areas west of Rochester. As the sfc high moves further off the East coast tonight...a deepening southerly flow featuring a modest 30-35kt low level jet will become established over our area ahead of a mid level shortwave and attendant sfc warm front. Lift provided by the low level jet over the sfc boundary will promote scattered shower activity after midnight...mainly over the western counties. Elevated CAPE averaging 200 j/kg could be enough within a synoptically forced environment to support a thunderstorm or two...with values as high as 500 j/kg over the Southern Tier being the most favored area. It will be notably warmer tonight than the past two...as the aforementioned deepening southerly flow and associated pronounced warm advection only allowing the mercury to drop to between 65 and 70 across the lake plains to the lower 60s most elsewhere. Back to summer. Saturday will then be quite unsettled...as a pair of boundaries will support numerous showers along with some thunderstorms. While there will be some dry time between the two rounds of pcpn...it will not be the nicest day for outdoor activities. Quite the contrary. First...a warm front will push northeast through the region during the morning. A 40kt low level jet impinging upon this sloping boundary will generate some showers and possible thunderstorms... but more numerous showers and storms can be expected during the midday and afternoon within a soupy sub tropical airmass in the wake of the warm front. A pre frontal trough will plow through this notably more humid airmass...and this will result in moderately heavy showers with some areas picking up torrential downpours and strong wind gusts within thunderstorms. The potential for localized heavy rain will be supported by PWAT values that will surge to nearly 2.25" and Td`s that will be within a degree or so of 70. As was astutely pointed out in earlier discussions...a measured PWAT value of 2.00 inches is uncommon for late June on radiosondes launched from the Buffalo Airport. Only 7 instances (12Z or 00Z) of a PWAT of 2.00 inches or more have been recorded since 1948. The exaggerated PWAT values will be a solid 2 standard deviations above normal...which for this time of year are outside the climatology 30 year return interval. Impressive. Basin average rainfall is forecast to range from a half inch or less over the Finger Lakes to nearly an inch elsewhere...with localized rainfall of 2 inches or more possible due to the sub tropical airmass and short MBE vectors (slow moving/back building convection). In regards to the risk for severe thunderstorms on Saturday...the advertised 40kt low level jet will promote an abundance of shear to the tune of 40-50kts through 6km. While this high level of deep layer shear could easily support organized convection...including some supercells...the question will be how much instability will be available given the forecast wealth of cloud cover. A minimum amount of 500 j/kg of MLCAPE should be expected with breaks of sun possibly allowing for as much as 1000 j/kg of SBCAPE. The main severe weather threat will be for damaging straight line winds...but the presence of supercells will also introduce a non-zero risk for tornadoes...mainly across the western Southern Tier. The greatest threat for any severe weather will be during the midday and afternoon. Otherwise...it will be a very breezy and muggy on Saturday with winds gusting to 30 to 40 mph outside of the aforementioned convection.
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&& .SHORT TERM /SATURDAY NIGHT THROUGH SUNDAY NIGHT/...
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Saturday evening a pre-cold frontal trough will push east across the region. This boundary will act to effectively shunt the plume of rich subtropical moisture (PWATs of 2 to 2.25 inches) eastward and out of our area...thereby bringing an end to the threat for heavier rain from west to east along with a commensurate decrease in precipitation coverage. Prior to its passage...the presence of ample deep-layer shear (0-6 km bulk shear values of 40-50 knots) could also lead to a risk for some strong to severe storms early in the evening...provided that sufficient instability can develop during the preceding afternoon - a factor that remains highly uncertain at this juncture. If realized...this risk would be greatest from the Finger Lakes westward...as is advertised by the Slight Risk area in SPC`s latest Day 2 Convective Outlook. As mentioned in the near term section above...the main severe threat would be for damaging wind gusts...though there would also be a non-zero secondary risk of a tornado. During the second half of Saturday night we can expect a continued potential for some scattered showers (more numerous across the North Country) and perhaps a couple more isolated thunderstorms as low pressure tracks across central Quebec and pivots its initial trailing cold front to our western doorstep. This being said...the loss of the subtropical moisture plume and diminishing instability should help to keep this activity of considerably lesser consequence than that of Saturday afternoon and evening. Otherwise it will remain very warm and muggy with the surface cold front remaining to our west through the night...with overnight lows mostly ranging between 65 and 70. On Sunday the initial cold front will slide across our region during the morning...with its passage marked by some additional scattered showers and isolated storms. In its wake cooler and drier air will overspread our region through the balance of the day and lead to generally dry weather from the Finger Lakes westward...though the approach of the supporting mid-upper level trough and an associated secondary cold front should keep the potential for at least some more scattered showers going right through the day east of Lake Ontario. With 850 mb temps dropping into the mid to upper single digits and surface dewpoints also falling through the 50s...both temperatures and humidity levels will become much more pleasant... with most areas seeing highs in the upper 60s to mid 70s. Sunday night the core of the mid-upper level trough and secondary cold front will slide south across our region...while supporting a few more widely scattered to scattered showers. As was the case with our last system...the potential for these will be greatest across the North Country where forcing again looks to be the most favorable. Otherwise the cool airmass (850 mb temps down to around +5C to +6C) should prove sufficiently cool enough to generate a fair amount of lake and orographically-induced cloud cover south and southeast of the lakes...with the latter also likely helping to preclude much in the way of river fog development across the Southern Tier. 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.
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&& .LONG TERM /MONDAY THROUGH THURSDAY/...
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Monday and Tuesday sprawling Canadian high pressure will slowly meander its way from the Upper Great Lakes to the mid-Atlantic coastline...while low-amplitude upper level ridging builds across the region aloft. This will provide us with fine weather for the first couple days of 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. This being said...surface dewpoints will remain confined to the 50s even on Tuesday...so it will remain comfortable in spite of the increasing warmth. Wednesday and Thursday broad/flat troughing will develop aloft... with associated surface low pressure passing by well to our north and eventually easing a weak trailing cool front across our area. This will lead to a renewed potential for at least some scattered showers and thunderstorms during this time. Otherwise a continued south to southwesterly flow out ahead of this boundary will pump warmer and more humid air back into our region for Wednesday...when high temps and surface dewpoints will likely climb back to between 85-90 and the mid-upper 60s respectively. Following the passage of the weak cool front...slightly cooler highs in the lower to mid 80s then look to follow for Independence Day...though humidity levels will likely remain elevated.
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&& .AVIATION /08Z FRIDAY THROUGH TUESDAY/...
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While there may be some valley fog across parts of the Southern Tier early this morning...fair VFR conditions with light winds will be in place through the day...courtesy of high pressure that will move from western New York to Long Island by this evening. VFR weather will remain in place through the first half of tonight... then an approaching warm front will help to generate scattered showers late...mainly over the western counties. Alto-cu cigs this evening will lower to VFR level strato-cu overnight in most areas...although MVFR cigs will become likely towards daybreak Saturday across the Srn Tier. There will be the potential for some low level wind shear late tonight...especially across the Finger Lakes region. Outlook... Saturday...Localized restrictions in increasingly widespread showers and scattered thunderstorms...some of which may produce locally heavy rainfall. Sunday...A chance of a leftover shower or two...otherwise mainly VFR. Monday and Tuesday...VFR.
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&& .MARINE...
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High pressure overhead early this morning will exit to Long Island by late this afternoon. This will allow gentle southeast winds early today to freshen a bit this afternoon while becoming more easterly. Wave action will be negligible. As the area of high moves off the coast tonight...a warm front will approach the region from the south. Winds will respond by veering back to the south and freshening overnight while remaining below small craft advisory criteria. It will then become quite unsettled on Saturday. Widespread showers and possible strong thunderstorms will develop in the wake of the aforementioned warm front during the course of the day...while fresh to strong southerlies will generate more pronounced wave action. Conditions may stay just below SCA levels...although conditions will become choppy...particularly well offshore. The area that may experience SCA conditions though will be the northeast corner of Lake Ontario...north of Mexico Bay. Fresh southwesterlies Saturday night will then freshen and become westerly on Sunday when SCA`s will be more likely...especially on Lake Ontario.
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&& .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...None. && $$ SYNOPSIS...RSH NEAR TERM...RSH SHORT TERM...JJR LONG TERM...JJR AVIATION...RSH MARINE...RSH