Area Forecast Discussion
Issued by NWS Buffalo, NY

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519 FXUS61 KBUF 192147 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 447 PM EST Fri Jan 19 2018 .SYNOPSIS... Breezy conditions will persist through tomorrow as our region remains sandwiched between a storm system passing across southern Canada, and a broad area of high pressure across the Southeast. This storm system may bring a few light snow showers or pockets of freezing drizzle to the North Country Saturday and Saturday night. There will be additional chances for light precipitation later Sunday and Sunday night as a warm front lifts across the region...a warm front that will also bring surface temperatures into the 40s for Monday. && .NEAR TERM /THROUGH SATURDAY/... Latest visible satellite imagery this afternoon displays skies clear across WNY, with the southern edge of the low clouds east of Lake Ontario beginning to erode. A few shallow snow showers/flurries remain east of Lake Ontario...with this activity rapidly coming to an end this late afternoon. At the surface a broad area of high pressure is found across the Southeast states, while a low pressure system is north of Lake Superior. This low will track across So. Canada tonight and tomorrow, with our region sandwiched between these two systems. Our region will remain dry tonight, though clouds will begin to fill in from north to south as the Canadian storm system nears. Warming in the lower levels will form an inversion...such that a 60 knot LLJ will remain above the boundary layer. However, an increasing pressure gradient between the two surface systems will maintain breezy conditions tonight and tomorrow...with occasional gusts 40 - 45 mph across along the Lake Erie shoreline, the northern Niagara Frontier and western Monroe County, and 25 to 40 mph elsewhere. Tomorrow will mainly be dry, with clouds thickening across the region as low level moisture increases. Westerly flow east of Lake Ontario will bring an upslope component...such that this saturated lower level may form patchy freezing drizzle or a flurry of snow. Confidence remains low at this point in time. Temperatures tonight will remain fairly steady with the southwest wind flow. Highs tomorrow will near 40F for many across the region. && .SHORT TERM /SATURDAY NIGHT THROUGH TUESDAY NIGHT/... Saturday night modest surface based ridging will maintain largely dry weather across our area...though skies will be mostly cloudy owing to plentiful low level moisture that will become increasingly trapped beneath a subsidence inversion. Any precip chances will be confined to the northeastern and southwestern ends of our area... with a dissipating backdoor cold front and upslope flow potentially leading to some patchy light snow showers or freezing drizzle across the North Country and Saint Lawrence Valley...and the western Southern Tier possibly seeing some very spotty drizzle/freezing drizzle owing to additional upsloping there. Have thus maintained slight chance to low-end chance PoPs in these areas...with the night otherwise expected to be dry. Meanwhile...low temps will range from the upper 20s to lower 30s. On Sunday diurnal warming will help to eliminate any spotty leftover freezing drizzle during the morning...with just some spotty drizzle or very light rain sprinkles then possible south of Lake Ontario during the afternoon owing to continued plentiful low level moisture... and a warm front that will slowly be extending eastward into our region from the Central Great Lakes. Otherwise...somewhat above normal temperatures will continue...with high temperatures ranging from the mid to upper 30s east of Lake Ontario to the lower 40s elsewhere. Sunday night and Monday low pressure over Kansas will track northeastward to around the Wisconsin-Illinois border...with its attendant warm front first extending further eastward into our region Sunday night...before slowly lifting northward toward Lake Ontario during the course of Monday. Slowly increasing warm air advection/isentropic lift and deepening moisture out ahead of the warm front will bring slowly increasing chances for some spotty light precipitation Sunday night...followed by a better likelihood for some precip on Monday as the warm front slowly lifts northward across areas south of Lake Ontario. Projected model soundings and statistical guidance both suggest that ptype during this timeframe will initially feature a rain/snow/sleet mix Sunday night...with this then going over to mostly rain during Monday as the atmospheric column continues to warm. During Monday...the various guidance packages continue to disagree on how quickly/exactly how far the warm frontal boundary lifts northward across areas south of Lake Ontario...with the 12Z/19 GFS/GEM remaining on the faster/more aggressive side of the guidance envelope...while the ECMWF remains a bit slower/more suppressed overall. Exactly how quickly/how far north the front pushes will have big implications on both precipitation coverage and temperatures south of Lake Ontario Monday afternoon...with the faster solutions supporting the potential for a relatively dry period with temperatures pushing into the 50s... while the slower solutions keep things wetter and notably cooler. Given the resultant forecast uncertainty/bust potential...for now have opted to take a middle ground with the temperature forecast for Monday. Monday night and Tuesday the surface low will track northeastward across the central Great Lakes and into southern Quebec...and in the process will finish pushing the warm front across our area Monday night...followed by its trailing cold front on Tuesday. Plentiful lift and moisture accompanying the warm and cold frontal passages will translate into fairly high probabilities for widespread precipitation during this period...and as such have continued to push PoPs higher into the categorical range. With a mild airmass in place...the majority of this will just fall as plain rain Monday night into Tuesday morning...before mixing with and/or changing to wet snow Tuesday afternoon as cold advection sets up following the cold frontal passage. The one possible exception to this evolution in ptype will be across the North Country and Saint Lawrence Valley... where the initial lingering northeasterly flow/colder low level air out ahead of the cold front could lead to a brief wintry mix Monday night...before the warm front passes through and forces a changeover to all rain by Tuesday morning. As has been pointed out previously...the combination of the above rainfall and increased snowmelt from higher temperatures and dewpoints may eventually bring some flood concerns by later Monday and Monday night. While this warm-up is not as dramatic as that of last weekend and overall rain amounts are also likely to be lower given the fast passage of the cold front...there may still be some potential for ice jam flooding in the late Monday-Monday night-Tuesday time frame. In the wake of the cold front...a westerly flow of colder air will continue to deepen across the area Tuesday night. Coupled with a trailing region of wraparound moisture behind the departing low... this will bring some scattered snow showers to the area...with some lake/orographically-driven snows also likely to set up east of Lake Ontario as the cold air deepens. Meanwhile off Lake Erie the lake response may be weaker owing to the presence of continued ice cover... so have gone with somewhat lower PoPs there to account for this. && .LONG TERM /WEDNESDAY THROUGH FRIDAY/... A low amplitude...Pacific air dominated pattern over the Lower 48 at the start of this period will experience significant amplification as we head towards the end of the week. The impetus for this evolving pattern will be a series of strong shortwaves that will slam into the West Coast and lead to broad troughing over the western half of the country. This in turn will promote a burgeoning progressive ridge over the Ohio Valley and Great Lakes regions that will eventually pump another period of very mild weather into our region for next weekend (just outside of the scope of this forecast). Breaking this down on a day to day basis... We will begin this period with temperatures trending lower...as a deep cyclone exiting across the Canadian maritimes Wednesday and Wednesday night will circulate a fresh batch of relatively cold air across the Lower Great Lakes. While the bulk of the synoptic moisture from this storm will be stripped away from our region by Wednesday morning...there will be enough low level moisture around to support some minor accumulations of lake effect snow...especially southeast of Lake Ontario. Have raised pops to likely for sites southeast of both lakes for Wednesday...with high chc pops now in place for the same areas Wednesday night. It will be partly to mostly cloudy outside of these lake snows. As ridging starts to build across the Upper Great Lakes on Thursday...warm advection will begin over our region with significant drying taking place between H925 and 850. This will bring an end to the nuisance lake snows by early afternoon. The axis of a large surface high will cross our forecast area Thursday night and Friday...during which time steady warm advection will push our H85 temperatures into positive territory. This will set the stage for notably nicer weather across our region...as temperatures should climb back into the 40s across the western counties for Friday afternoon. && .AVIATION /22Z FRIDAY THROUGH WEDNESDAY/... For the 18Z TAFS VFR flight conditions are found across WNY, while lingering low clouds and shallow lake effect snow continues east of Lake Ontario...including the KART airfield. Flight conditions will largely remain MVFR within this light snow...with brief IFR visibilities. Activity will diminish through the afternoon as warming continues aloft. A LLJ of 50 to 60 knots tonight will bring LLWS across the 4 Western NY TAF sites. A strengthening inversion in the lower levels should prevent these strongest wind gusts from mixing to the surface...though winds may still gust into the 25 to 30 knots range. VFR flight conditions tomorrow morning...though as moisture returns we`ll see ceilings fall back into the MVFR range. Outlook... Saturday night through Sunday...Widespread MVFR ceilings persisting through Sunday. A chance of rain/snow late. Monday and Monday night...MVFR/IFR with rain showers developing. Tuesday...MVFR/IFR with rain showers changing to snow showers before ending...then areas of lake effect snow also developing east of the lakes Tuesday night. Wednesday...VFR/MVFR with a chance of snow showers. Thursday...Mainly VFR. && .MARINE... A moderate to strong pressure gradient between an area of low pressure crossing Southern Canada and surface high pressure over the Southeast will maintain breezy conditions on the Lakes, and the Upper Niagara River. A small craft advisory will remain in effect for the Lakes, as well as the Upper Niagara River. High pressure will reach the Eastern Great Lakes region Sunday that will relax the winds and allow for wave heights to diminish. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...None. MARINE...Small Craft Advisory until 10 PM EST Saturday for LEZ040-041. Small Craft Advisory until 1 PM EST Saturday for LEZ020. Small Craft Advisory until 4 AM EST Sunday for LOZ042>045. && $$ SYNOPSIS...THOMAS NEAR TERM...THOMAS SHORT TERM...JJR LONG TERM...RSH AVIATION...THOMAS MARINE...THOMAS

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