Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 251054 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 654 AM EDT SUN SEP 25 2016 .SYNOPSIS... A large area of high pressure centered over eastern Canada will push east this afternoon and tonight...and this will guarantee another sun filled day to end the first weekend of Fall. A strong cold front will then plow across Western and North Central New York late Monday and early Monday night...producing several hours of showers and possibly some thunderstorms in the process. Colder air in the wake of the front will generate some lake effect rain showers northeast of both lakes on Tuesday. && .NEAR TERM /THROUGH TONIGHT/... Expansive high pressure stretching from Baffin Island and Quebec to the Carolinas will assure us of another beautiful early Autumn day across the region...as sun filled skies will accompany seasonable temperatures in the 60s. The `tea kettling` cloud cover that was originally anticipated near the south shore of Lake Ontario early this morning was short circuited by a drier than expected environment. The 00z KBUF sounding depicted a much wider T/Td spread in the lowest layers than what was suggested by earlier BUFKIT soundings. This...along with a great deal of shear below 5k ft...greatly limited any lake response so that only scattered strato-cu developed overnight and has since largely dissipated. The only additional cloud cover that we will see today will be some streaks of cirrus and alto-stratus that will spill over the highly amplified mid level ridge to our west. As mentioned...temperatures will climb to near seasonal levels for the afternoon...a carbon copy from Saturday. Tonight...the axis of the surface high will push east across New England. This will allow for some weak warm advection to get underway as high and mid level cloud cover will thicken over the western counties during the course of the night. While this should help to hold temperatures up several degrees higher over the western counties than those from this morning...there will likely be another round of frost tonight for Lewis Co where starlit skies will prevail. Since there is already a frost advisory in effect for that county for the remaining early morning hours...will refrain from issuing another one until later this morning to avoid confusion. Thanks BTV, ALY and BGM for collaboration with this. && .SHORT TERM /MONDAY THROUGH WEDNESDAY NIGHT/... Monday and Monday night...our weather will deteriorate as surface- based ridging over Eastern New York and New England at the start of the day slides east into the Canadian Maritimes...and gives way to a deep mid and upper level trough digging southeastward across Ontario Province and the Great Lakes...with this feature eventually morphing into a deep closed upper low over Central Ontario by Tuesday morning. At the surface...an attendant surface wave will meander along a similar path...and will swing its trailing cold front through our region between late Monday afternoon and Monday night. As the front passes through our region...it will be accompanied by a narrow but impressive band of deep moisture (PWATs of 1.5 to 1.75 inches)...as well as an equally impressive swath of deep-layer lift driven by the front itself...and strong height falls/DCVA/diffluent flow aloft. All of this should lead to a narrow but fairly cohesive band of showers traversing our region from west to east...for which categorical PoPs look very reasonable and thus remain in play. Given that some weak instability will also be in place...a few embedded thunderstorms will also be possible across far WNY and western portions of the Finger Lakes from Monday afternoon into early Monday evening...before fading out with the loss of heating after sunset. Following the passage of the front...strong dry slotting aloft will build into the region Monday night...while bringing a return to mainly dry weather for many areas. This break will not last very long northeast of Lake Erie though...as a sheared southwesterly flow of progressively cooler air and a modest increase in low-mid level moisture should be sufficient to drive the development of some scattered lake effect rain showers overnight...with these initially forming a little south of Buffalo...then lifting northward across the Niagara Frontier in response to a subtle but steady backing of the low level flow. With respect to temperatures during the first 24 hours of this period... the strengthening southerly downslope flow and the overall warm air advection regime out in advance of the cold front will allow temps to rebound back into the lower to mid 70s across much of the region on Monday...with only interior portions of the North Country likely confined to the mid and upper 60s. The warmest overall temps will be found across the lake plains of far Western New York where the above mentioned downslope flow will be most favorable...and where we have accordingly continued to aim a bit above current MET/MAV guidance. Developing cool air advection in the wake of the cold front will then send readings tumbling back into the upper 40s to mid 50s Monday night. Tuesday and Tuesday night...the large (and now closed-off) upper low will slowly meander its way south-southeastward across the state of Michigan...with our region remaining firmly under of the influence of its accompanying cool pool (850 mb temps of +4C to +7C)...though the best and deepest associated wraparound moisture will generally remain to our west...with just an attending spoke of this sliding across far Western New York and adjoining portions of Lake Erie/Lake Ontario. Thus for most locations...Tuesday and Tuesday night should just be mainly dry and cooler...with highs ranging through the 60s on Tuesday and nighttime lows falling into the mid 40s to lower 50s Tuesday night. The exceptions to this will of course be over and downwind of Lakes Erie and Ontario... where the cool airmass aloft and warm lakes will help to generate some lake effect rain showers. Overall the best setup will be found over and downwind of Lake Erie Tuesday morning...where a somewhat sheared southwesterly low level flow and the aforementioned spoke of deeper moisture will be supportive of more numerous showers across much of the Niagara Frontier...though the combination of the shear and late September diurnal influences will probably help keep these from evolving into a cohesive rain band... especially as diurnal effects increase later on Tuesday morning. After that time...the combination of diminishing background moisture... a slow but steady backing of the low level flow...and a further increase in shear will result in the showers weakening/becoming more scattered and lifting northward into Niagara County Tuesday afternoon and evening...before shifting west of the area and falling apart altogether Tuesday night as our airmass becomes too dry and the low level flow too southerly. Meanwhile off our other lake...the overall setup appears less impressive as background moisture will be less favorable...and the low level flow will likely be a bit more sheared and south- southwesterly overall. This should result in much more scattered showers primarily across Jefferson County and the uppermost Saint Lawrence Valley on Tuesday...with this activity then also shifting further northwestward and falling apart altogether Tuesday night as the airmass dries out and the low level flow backs to southerly. During Wednesday and Wednesday night...the closed upper low and its original surface reflection will continue to meander south-southeastward into the Ohio Valley. For our region...an initial southerly flow of drier air on the eastern flank of this system should result in a mainly dry and slightly warmer day for most of Wednesday...before increasing moisture and lift associated with the encroaching northern portion of the low leads to a renewed potential for some scattered showers later Wednesday afternoon and night. Temperature-wise...highs on Wednesday should range between 65 and 70 in most places...with lows in the mid 40s to lower 50s then following for Wednesday night. && .LONG TERM /THURSDAY THROUGH SATURDAY/... Later on in the week forecast confidence decreases markedly...as much disagreement remains amongst the medium range guidance packages with respect to the eventual evolution/movement of the lingering closed low. More specifically...the 00z/25 GFS/Global GEM both continue to meander this feature eastward across the Mid-Atlantic and Northeastern States Thursday and Friday...which would support a continued general chance for some showers through the end of the work week...followed by a return to dry weather for next Saturday as high pressure builds in behind the departing system. Meanwhile the ECMWF continues to stick with its idea of taking the closed low due southward into the Tennessee Valley on Thursday...before lifting it back north toward the Central Great Lakes Friday and Saturday...a solution that would favor drier weather for our area Thursday...followed by increasing shower chances again for both Friday and Saturday. Given the poor model-to-model and run-to-run consistencies that thus continue to plague this time frame...and our previous continuity of a mainly dry forecast...for now will elect to lean more towards continuity and only trend the forecast a little more pessimistic for the latter portions of the week...with a low chance of showers Thursday (as per the GFS/GEM) followed by slight chance PoPs for both Friday and Saturday... along with continued near to slightly above normal temperatures. && .AVIATION /12Z SUNDAY THROUGH THURSDAY/... Expansive high pressure stretching from Hudson Bay to the Carolinas will provide VFR conditions across our region through tonight. The only possible exception will be across the Western Southern Tier where there could be some leftover valley fog through about 13z. Outlook... Monday...While VFR weather will prevail for most sites...showers and possible thunderstorms will arrive in the far west after 18z to produce localized MVFR conditions. Monday Night...Areas of MVFR with showers likely. Tuesday and Wednesday...VFR/MVFR with a chance of showers. Thursday...Mainly VFR. && .MARINE... A large area of high pressure centered over Quebec will keep a northeasterly flow of chilly air across the Lower Great Lakes today. The flow will be strong enough to generate small craft advisory conditions on the Lake Ontario nearshore waters west of Hamlin Beach and also on the Lower Niagara River. Choppy...sub advisory conditions will be found on Lake Ontario from Hamlin Beach to Sodus Bay and also on Lake Erie southwest of Dunkirk. The surface high will push east across New england the St Lawrence Valley tonight. This will encourage winds to veer to the southeast...thus removing the choppy conditions described above as the highest waves will move into Canadian waters. The southeast winds will freshen on Monday ahead of an approaching cold front...with the winds coming around to southwest by late Monday and Monday evening. Winds should freshen enough to warrant a new round of small craft advisories by late Monday. SCA conditions are then expected to persist through Tuesday as a stationary storm system will be parked over the Upper Great Lakes. && .CLIMATE... Saturday marked the end of the longest stretch of 70+ degree days in Buffalo and Rochester since records began in the early 1870s. The high temperature Saturday topped out at 65 for Buffalo and 64 for Rochester...which marks 102 days since the last time (June 13th) that the high temperature did not reach the 70 degree mark. Following is a top ten list of longest stretches of 70+ degrees days for Buffalo and Rochester. Buffalo Rank Run Length Ending date 1 102 2016-09-23 2 95 2005-09-22 3 94 2012-09-08 4 80 1959-09-10 5 78 2006-08-28 6 77 1878-09-10 7 75 1993-08-20 - 75 1987-08-23 9 73 1980-09-11 10 71 1952-08-21 Rochester Rank Run Length Ending Date 1 102 2016-09-23 2 101 2002-09-26 3 88 2005-09-15 4 84 1959-09-10 5 83 1939-09-04 6 82 2011-09-04 7 81 1975-08-29 8 79 1881-09-12 9 78 2006-08-29 10 75 2012-09-08 && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Frost Advisory until 9 AM EDT this morning for NYZ007-008. MARINE...Small Craft Advisory until 4 PM EDT this afternoon for LOZ030- 042. && $$ SYNOPSIS...RSH NEAR TERM...RSH SHORT TERM...JJR LONG TERM...JJR AVIATION...RSH MARINE...RSH CLIMATE...STAFF

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