511 FXUS61 KBUF 061135 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 635 AM EST Sat Jan 6 2024 .SYNOPSIS... Low pressure over the southeastern states will become better organized as it tracks northeastward and off the mid-Atlantic coast today and tonight...then offshore of New England on Sunday. This system will bring a light to modest accumulating snowfall to our region this afternoon through Sunday. The greatest accumulations will extend across the interior of the Southern Tier...Finger Lakes...and North Country...while the lowest amounts will be found across the Niagara Frontier. Following the passage of this system... high pressure will build in Sunday night and Monday and bring a return to fair dry weather. && .NEAR TERM /THROUGH SUNDAY/... Through the course of today and tonight a broad mid-level trough initially centered over the Mississippi Valley will push across the Ohio Valley and Great Lakes. On its southeastern flank...height falls/DCVA aloft attendant to a passing strong shortwave will spur a broad surface low over the southeastern states to lift northeastward to the Delmarva region and become better organized today...then track a bit south of the southern New England coast while continuing to intensify tonight. At the same time...a broad inverted surface trough will develop and extend back westward from the developing coastal low to a second and much weaker surface low pushing into the Upper Great Lakes...with the axis of this trough settling across western New York later on tonight. The developing coastal system will send an initial swath of deeper Atlantic-based moisture and warm advective forcing across our region during the course of this afternoon and evening...with the latter aided by convergence at the nose of a developing southeasterly low level jet and a broadly diffluent flow aloft. After a dry and quiet morning...this will result in a period of widespread light to moderate snow overspreading our region from southwest to northeast this afternoon and evening. The latest guidance has trended a little bit slower with the arrival of the snow and have accordingly adjusted the forecast to account for this...with the steadier snow currently expected to first arrive across the Southern Tier during the early to mid afternoon hours...then across the Niagara Frontier and Finger Lakes between late this afternoon and early this evening...and the North Country this evening. Still expect this initial batch of snow to be steadier/slightly heavier and longest lasting from the Southern Tier northeastward across the Finger Lakes and North Country...all of which will lie closer to the developing coastal system and the better large-scale forcing and deepest moisture. Meanwhile further to the northwest across the Niagara Frontier over to about Rochester...this first batch of snow will be lighter and not quite as long lasting. After about mid-evening...the snow should tend to temporarily decrease in both coverage and intensity from west to east as the low level jet and initial surge of warm advective lift slides eastward. This being said...still expect at least some light snow to continue at times through the overnight hours given the lingering deep cyclonic flow and copious amounts of moisture below 10-12 kft...as well as the incoming inverted surface trough axis. With this in mind...have elected to at least somewhat dampen the temporary trend toward drier weather previously advertised in continuity. With respect to snowfall accumulations between this afternoon and tonight...have trended these just a a little bit upward from the previous forecast given a continued gradual northwesterly shift in the forcing/attendant QPF from the coastal system. With these changes...have a general 3-6" indicated from Allegany county through the interior/eastern Finger Lakes and interior portions of the North Country...with amounts tapering back to a general 1-3" across extreme far western New York. Late tonight and Sunday the coastal low will continue to strengthen as it tracks offshore of the southern New England coastline. While this feature will be pulling further away from our region as it does so...we'll still have to contend with the aforementioned inverted trough/broad cyclonic flow lingering across our region...which coupled with the arrival of a swath of deeper wraparound moisture will help to support some additional light snow/snow showers...which will be most prevalent and steadiest across North Central New York. As the axis of the inverted trough shifts eastward through the day...a westerly to west-northwesterly flow of marginally cold enough air for a lake response will develop and also lead to the development of areas of weak to modest lake/orographic enhancement east and east-southeast of both lakes. Additional accumulations during Sunday should range from 1-2 inches across the North Country and east-southeast of both lakes to a half inch to an inch or so elsewhere. Regarding our winter weather headlines...have only made a couple minor tweaks to add Livingston and Jefferson counties to the existing Winter Weather Advisories given the aforementioned subtle northwestern shift seen with the first round of snow/associated forcing this afternoon and tonight. Otherwise these still look reasonable. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... Pcpn across the region will continue to taper off Sunday evening... as a sfc trough reaching back from a coastal low will exit to the northwest. In the process...mid level moisture will be stripped away...leaving only enough to interact with lake effect instability. Additional snow accumulations will be under a half inch for the vast majority of the forecast area...with an inch or two possible southeast of Lake Erie. A burgeoning ridge will build across the Upper Great Lakes Monday before exiting via New England Monday night. Outside of some insignificant lake snow showers southeast of Lake Ontario Monday morning...this will guarantee fair dry weather through this 24 hr period. && .LONG TERM /TUESDAY THROUGH FRIDAY/... ...Strong Winds Tuesday and Wednesday... There is increasing confidence that a powerful storm system will pass just to the west of our forecast area during the first part of this period. While at first glance this scenario has many earmarks of a classic high wind event...there some key components that may be missing. For instance...despite the very dynamic nature of this system...guidance is not indicating significant trop folding nor a strong low level jet in the cold sector of the storm. This will certainly have to be followed up in later model runs. As we open this period on Tuesday...a highly exaggerated pattern within the southern branch of a split flow will feature an anomalously deep -5 STD H5 trough over the southern Plains...while a broad ridge will be making its way off the East coast. This very energetic pattern will include a rapidly deepening sfc low that will strengthen to roughly 984mb while it will make its way up the Ohio valley on Tuesday. Ahead of this storm system...a divergent flow aloft and a 50kt low level jet riding up across our region will set the stage for some widespread over our region. While this pcpn will initially be in the form of light snow...the deep warm advection will quickly force the pcpn to rain over the western counties. Meanwhile across the North country...a mix of rain and snow can be expected for much of the day. More importantly on Tuesday...a 60-70kt southeasterly LLJ will come into play near the Chautauqua ridge. Strong downslope winds will be possible with gusts over 45 mph between Lake Erie and the ridge... but if the pcpn is steady enough...this threat will be minimized. Tuesday night...the ever strengthening sfc low will track very close to our forecast area while deepening to between 975-980mb...some 3-4 STD below climatology for this time of year. The advertised tracks range from JUST west of the Niagara River (as per the ECMWF/GFS)... to directly over our forecast area (GGEM). Neither track is good... as strong to high winds will be within the realm of possibilities. Widespread rain will be found ahead of the impressive storm system for much of the night...although mid level 'dry' air sweeping northwards across the western counties should encourage the pcpn to taper off. This should not be the case east of Lake Ontario. Rainfall amounts for Tuesday and Tuesday night are forecast to range from three quarters to one inch. Given that most areas do NOT have much of a frost depth (if any)...this should saturated the sfc and potentially weaken shallow rooted trees. Something to keep in mind. The main issue Tuesday night through will be the potential for strong to high winds. Winds of 55-60 kts in the warm sector will maintain the threat for strong downslope winds near the Chautauqua ridge and also on the northern slopes of the Tug and within the Black river valley where funnelling could be an issue. The powerful area of low pressure will lift north-northeast of our forecast area during the day Wednesday. It will most certainly be windy...but factors including storm track...intensification trend and strength of low level jet will make the final determination. All of these variables vary somewhat in the various guidance packages. Meanwhile...more showery mixed pcpn in the morning will tend to become less widespread during the course of the day. The exception of this will be east of Lake Erie where the deepening cold air in the wake of the strong storm system will encourage some lake snow to develop. Sfc based ridging will then cross the region Wednesday night and Thursday. This will grudgingly allow winds to slowly subside during the course of the night...while relatively cold air will support at least scattered lake snow showers east of both lakes. Most of the region will experience uneventful weather though during this 24 hr period. A shortwave ridge will cross our region Thursday night to provide us mainly fair weather...then the NEXT significant storm system will take aim on us for Friday. This next storm is initially forecast to be similar to the one from earlier in the week...complete with another soaking rain and potential for strong to high winds. One possible change with this system though is that some guidance packages are leaning toward some accumulating snow with it. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... Regional satellite imagery and surface obs continue to show a widespread swath of MVFR clouds in place from northern portions of the Niagara Frontier and Finger Lakes northward to the North Country. These will continue to slowly recede northward through course of the early afternoon hours. This being said...plenty of high and mid clouds will also continue to overspread the region as the lower clouds dissipate...so where MVFR ceilings are still in place these will only improve to around 10 kft or so. Where the lower ceilings have already dissipated...ceilings of 15-25kft will gradually lower to the 8-10 kft range through this morning. Conditions will then deteriorate to IFR in increasingly widespread light to moderate snow from south to north this afternoon and evening as organizing low pressure over the southeastern states moves to and then offshore of the mid-Atlantic coastline. While the steadier snow will then tend to pull eastward into central New York from later this evening through the rest of tonight...fairly widespread IFR/lower-end MVFR conditions are expected to persist across the region in lower ceilings/lingering lighter snow. Outlook... Sunday...Periods of light snow with MVFR/IFR. Monday...Mainly VFR. Tuesday...Snow and rain developing, changing to mainly rain later Tuesday and Tuesday night. Deteriorating to MVFR/IFR. Very windy. Wednesday...Rain changing back to snow, with areas of MVFR/IFR. Very windy. && .MARINE... Freshening easterlies well out ahead of a developing coastal low will result in another round of advisory-level conditions for western portions of Lake Ontario this afternoon through the first half of tonight...for which a Small Craft Advisory has been hoisted as outlined below. These easterlies and corresponding elevated wave heights will then subside later on tonight as the coastal system begins to depart...with the flow then backing to northwesterly and remaining modest on Sunday. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Winter Weather Advisory from 4 PM this afternoon to 4 AM EST Sunday for NYZ004-005-013-014. Winter Weather Advisory from 7 PM this evening to 7 PM EST Sunday for NYZ006>008. Winter Weather Advisory from 1 PM this afternoon to 4 AM EST Sunday for NYZ021. MARINE...Small Craft Advisory from 10 AM this morning to 4 AM EST Sunday for LOZ042-043. && $$ SYNOPSIS...JJR NEAR TERM...JJR SHORT TERM...RSH LONG TERM...RSH AVIATION...JJR MARINE...JJR