Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 110019 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 719 PM EST Sun Dec 10 2017 .SYNOPSIS... Lake effect snow will continue east of Lakes Erie and Ontario this evening and tonight with locally heavy snowfall. The lake effect snow will quickly end Monday morning as high pressure briefly builds into the eastern Great Lakes. Low pressure will then cross the region Monday night through Wednesday with periods of widespread accumulating snow. Several additional weak systems will cross the area late in the week with additional chances of snow. && .NEAR TERM /THROUGH MONDAY/...
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Lake effect snow will continue to be the main focus through tonight. A weak clipper passing to the north of Lake Ontario this evening will force boundary layer flow to back to the WSW, and also force better moisture and convergence over the lakes. Lake Induced equilibrium levels will remain around 10K feet, with ample moisture and a deep dendritic crystal growth layer beneath the inversion. The favorable thermodynamics, synoptic support, and deep moisture should promote snowfall rates approaching 2 inches per hour off both lakes through the first half of tonight in the strongest portion of the bands. Off Lake Erie... A band of lake effect snow will linger across the Southtowns through about 10 or 11pm before heading farther south overnight. Travel conditions will continue be very poor during this time in the band with heavy snow bringing very low visibility and deep snow cover on roads. The inland extent has increased with increasing moisture ahead of the upper-level trough. Expect this will spread advisory level (3 to 6 inch) snows into southwest Monroe and northern Livingston counties this evening, making for slippery travel and poor visibility there. By mid to late evening, boundary layer flow will begin to veer again, carrying the band of snow back south across the Buffalo Southtowns and into Southern Erie/Wyoming counties. The band will likely move onshore along much of the Chautauqua County shoreline overnight, then transition into weaker upslope/lake enhanced snow late tonight across the Chautauqua Ridge. Storm total accumulations are expected to reach 8-12 inches from central/southern Erie County into southwest Genesee, western Wyoming, northern/western Chautauqua County, and northwest Cattaraugus county. Some local amounts may come in with up to 14 inches in the nearby Buffalo Southtowns if the band stalls there long enough. Off Lake Ontario... A trough will approach the lake tonight and force a strong band of convergence to develop, allowing the band of snow to intensify further across central Jefferson and northern Lewis counties. This band will then drop south into the Tug Hill region overnight, with a period of very high snowfall rates over the northern Tug Hill. Finally, late tonight the band will drop to the southeast corner of the lake and rapidly weaken as flow becomes WNW and shear increases. Expect storm total accumulations to reach the 8-12 inch range across southern and central Jefferson County, northern Oswego County, and northern/western Lewis County. There may be a narrow strip across the northern portion of the Tug Hill of up to 18 inches if the band stalls there long enough. By daybreak Monday any remaining lake effect snow will be in a much weakened state to the southeast of the lakes, as shear rapidly increases and inversion heights lower with weak high pressure building over the eastern Great Lakes. Any remaining impacts should be fairly minor for the Monday morning drive.
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&& .SHORT TERM /MONDAY NIGHT THROUGH WEDNESDAY NIGHT/... There is high confidence for a widespread general snowfall Monday night into Tuesday as a clipper low tracks across the Eastern Great Lakes into Northern NY. Plentiful synoptic moisture and lift will be forced by an anomalous 2-3 SD below normal, near 500dm, mid-level trough digging south across the Great Lakes. Additional support for widespread snow will come from warm advection near 850mb. A blend of 12z QPF guidance with SLR between 15:1 and 20:1 in a cooling airmass will bring a general 2-3 inches Monday night. As the surface low begins to center to the east of Lake Ontario Tuesday afternoon, winds will veer to west then northwest while becoming gusty in steeping low level lapse rates as cold advection sets in. Additional synoptic snow is expected areawide through Tuesday in wrap around moisture where another 2-3 inches will be possible. A Winter Weather Advisory may be needed especially if snow rates/totals come in higher with later guidance. Temperatures Monday night will dip into the teens and low 20s with highs into the mid 20s to around 30 Tuesday. Gusty winds in the wake of the systems cold front should run 20-30 mph especially south of the low center across the western Southern Tier driving wind chills into the teens. Later Tuesday into Wednesday we will see a transition into another potentially significant lake effect snow event with headlines possible. Lake effect snows are expected to develop south or southeast of the lakes as 850mb temps cool aloft. BUFKIT cross sections indicate healthy lake plumes with equilibrium heights running 10-15kft and sufficient synoptic moisture and lift intersecting the dendritic snow growth zone. Tuesday night into Wednesday will perhaps be the most significant time period of accumulating lake snows with equilibrium level peaking. With current Lake Effect headlines in effect and the best period for the next event still 3 days out we will continue with the mention in the Hazardous Weather Outlook. The core of the anomalously deep 500mb low will pass over our region Tuesday night and Wednesday which will bring the coldest air yet this month with lows dipping into the single digits to teens Tuesday night and only peaking in the teens to maybe 20 on Wednesday. Lake effect then continues to look like it will begin to weaken later Wednesday night as high pressure over the Ohio Valley is forecast to nose north into western NY. && .LONG TERM /THURSDAY THROUGH SUNDAY/... Medium range guidance continues to indicate two more clipper lows working across the Great Lakes later this week and next weekend. A fair amount of uncertainty remains regarding the timing and tracking of either of these clipper lows as well as any potenial lake enhancement. Have continued broadbrush chance POPs for snow showers through Saturday until more certain details arise in newer guidance. Temperatures will remain below average through the end of the week, as the region will remain embedded within longwave troughiness. The eastern trough may break down over the weekend which would potentially allow warmer air to return to our region. Blend of model temperature guidance indicates temps may rise back to normal by Saturday and possibly above normal for Sunday. If this occurs rain/snow would be possible Sunday. Longer range guidance suggests that this break from the cold may only be temporary, as a longwave trough becomes re-established over the East in the week following. && .AVIATION /00Z MONDAY THROUGH FRIDAY/...
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Bands of heavy lake effect snow will continue east of both lakes through tonight with local very low IFR within the bands. Outside of lake effect areas expect a few light snow showers with local MVFR CIGS/VSBY. Off Lake Erie, a band of very heavy snow will remain just south of KBUF this evening, and will move farther away from the terminal after 04Z. The eastern end of this band may bring some IFR to KROC as well for a few hours. Late this evening the band will move south and away from KBUF, with IFR developing at KJHW and the rest of the western Southern Tier overnight. The snow will rapidly weaken by Friday morning. Off Lake Ontario, a band of very heavy snow just south of KART will may clip KART/KGTB with IFR conditions at times. Overnight the band will move back south across the Tug Hill region, and end up at the southeast corner of the lake in a much weakened state by early Friday morning. Outlook... Monday...Lake effect snow showers with local IFR southeast of the lakes early, then improvement to VFR. Monday night through Wednesday...Areas of IFR with periods of snow. Thursday and Friday...Areas of MVFR/IFR with snow showers likely.
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&& .MARINE... Moderate westerlies will continue across the eastern Great Lakes through tonight with Small Craft conditions on both lakes. High pressure will then bring a brief period of lighter winds on Monday. Low pressure will pass directly overhead late Monday night and Tuesday morning. Winds will increase in the wake of this system later Tuesday through Wednesday, with another period of solid Small Craft Advisory conditions expected. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Lake Effect Snow Warning until 7 AM EST Monday for NYZ006>008- 012-019-020-085. Lake Effect Snow Warning until 1 AM EST Monday for NYZ010-011. Winter Weather Advisory until 1 AM EST Monday for NYZ003-013. MARINE...Small Craft Advisory until 7 AM EST Monday for LEZ040-041. Small Craft Advisory until 10 PM EST this evening for LEZ020. Small Craft Advisory until 10 AM EST Monday for LOZ043-044. Small Craft Advisory until 7 AM EST Monday for LOZ042-045. && $$ SYNOPSIS...CHURCH/HITCHCOCK NEAR TERM...CHURCH/HITCHCOCK SHORT TERM...SMITH LONG TERM...SMITH AVIATION...CHURCH/HITCHCOCK MARINE...CHURCH/HITCHCOCK

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