Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 082355 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 655 PM EST Thu Dec 8 2016 .SYNOPSIS... Cold air will cross the Eastern Great Lakes through Saturday, producing bands of lake effect snow that will oscillate along the southeast shores of the Lakes Erie and Ontario. Accumulations of snow may be measured in feet on the higher elevations to the east of the lakes, before diminishing in intensity later Saturday. An area of low pressure will then move through the Great Lakes region Sunday and Monday, producing a general snow for much of the region. && .NEAR TERM /THROUGH FRIDAY/... Strong bands of lake effect snow continue east of both lakes this evening, with snowfall rates around 2 inches per hour being reported in the stronger portions of each band. The Lake Erie band has been shifting very slowly south over the past few hours, just a few miles per hour, and expect this trend to continue through late evening. The Lake Ontario band has been pretty steady state focused on the southern Tug Hill, and will likely remain in place through mid to late evening. Through the night, a surface trough connected to the surface low tracking east across Quebec will drop across southern Canada and towards the Eastern Great Lakes. This trough will not only increase the low level lift and snowfall rates, but also begin to shove the lake effect snow southward. Off Lake Ontario overnight into Friday... The warm waters of Lake Ontario may delay the passage of the trough some through the night, but by dawn tomorrow morning northwest flow will be well established. During the trough passage, expect much of the east/west oriented band to be captured and moved onshore bodily, with a burst of snow moving south along the south shore of the lake from the Rochester area to Oswego County during the wee hours of the morning. Following this, multiple bands will likely develop in the northwest flow regime behind the trough. Snowfall rates will still be 1-3 inches per hour until the trough passage, then the lake effect snow will weaken significantly. On Friday a push of drier mid level air, and a shorter northwest fetch will greatly limit the intensity of lake effect snow southeast of the lake. Expect relatively light lake effect snow showers to continue from the Rochester area east to Oswego County, with only 1- 3 inches of accumulation in the more persistent bands. There will also be a Georgian Bay band meandering around, which may bring an inch or so of accumulation to the Niagara Frontier west of Rochester and northeast of Buffalo. Off Lake Erie overnight into Friday... The lake snow band east of Lake Erie will reorient to the new northwesterly wind overnight, forcing the stronger band of snow to shift southwest across Chautauqua and western Cattaraugus counties, with weaker multiple bands developing in its wake. There will also be a dynamic upstream connection developing late tonight to the snow off southern Lake Huron to seed the band off Lake Erie. This upstream connection will be the main focus for the heaviest snowfall rates for Friday. Expect this to drift into far western Chautauqua County near Findlay Lake during the morning and possibly into Erie County PA for a time, before moving back east and into Chautauqua County later in the afternoon. This band with an upstream connection may still produce 1-2 inch per hour snowfall rates. Otherwise across the rest of the western Southern Tier, weaker multiple bands and weaker upslope flow will bring occasional light to moderate snow showers. There will also be a gusty wind this period, especially around the edges of the lake effect snow bands tonight. Wind gusts may near 30 to 35 mph that will bring additional blowing and drifting to the snows. Air temperatures will be seasonable this period...with overnight lows remaining in the 20s. High temperatures on Friday will not be much warmer with readings in the upper 20s to the lower 30s. && .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY NIGHT/... A 290 to 300 degrees low level flow should be in place Friday night, continuing to focus the heavier lake snows into the western Southern Tier off Lake Erie and into Northern Wayne and Cayuga counties, perhaps clipping Northern Monroe county. Over-lake instability continues to be impressive with lake induced CAPES around 700 j/kg and lake equilibrium levels between 10k-15k feet. This suggest that snowfall rates will continue to be in excess of an inch per hour. Additional accumulations Friday night could be significant within the warning areas. Steering winds will gradually back late Friday night and Saturday as the upper level trough gradually weakens. This will bring low level winds from 290/300 degrees to 240/250 by Saturday afternoon/evening. Expect the band off Lake Erie to remain organized as it briefly focuses on Southern Erie county before lifting north across the Buffalo metro area. Amounts will be limited due to the transitory nature of the band, but depending on how intense the band it, it is possible that several inches of snow could push into the Buffalo metro area during the day Saturday. By Saturday night, the flow should continue to back to more southerly which would push whatever lake effect snow to our west. A similar story will play out off Lake Ontario, with lake effect snows lifting northward. Sunday and Sunday night, the above mentioned backing flow is expected ahead of the next system expected to arrive during this time period. Consensus model blend would suggest that isentropically driven snow arrives very late Saturday night or early Sunday, continuing through into Sunday night. This system does have a tap into Gulf moisture, with profiles showing deep moisture through the dendritic growth zone which would help snowfall rates. It is very possible that several inches of widespread snow will fall Sunday into Sunday night with another possible winter weather headline event looming. && .LONG TERM /MONDAY THROUGH THURSDAY/... There continues to be a high likelihood of wintry weather persisting into next week as a much colder arctic sourced airmass is forecast to dive south towards the Great Lakes region. This arctic air may bring the coldest temperatures that we have seen this season by mid to late next week. The 08/12z GFS and EC continue to show potential for a closed surface low tracking across the eastern Great Lakes Monday but remain in some disagreement with regards to the strength of this low. These models have flip-flopped when compared to 07/12z runs with the GFS now the deeper low near 992mb tracking just to the northwest of Buffalo while the EC is weaker than yesterday only showing a 1007mb low tracking along the NY/PA state line. Have included likely POPs for Monday as both models do show sufficient lift and moisture but the strength of the winds will end up coming down to the exact depth of the low. The deeper GFS scenario would bring a much stronger wind field with potential for very gusty winds. This storm will lead in a deep sub-500dm closed low shifting south out of the Arctic to somewhere between the Great Lakes and James Bay by mid next week. The models are showing separation in the placement of this mid level low which has origins from near the pole. This disagreement is keeping a lower confidence in exactly how cold of an airmass reaches western and central NY mid to late week. The GFS is showing 850mb temps in the -20s C reaching our forecast area while the EC only shows negative teens C. While both airmasses could support lake effect snows if enough background moisture is available, the colder airmass would lead to steeper lapse rates and more intense snow bands. Have continued medium chance POPs for lake snows east of the lakes Tuesday into Thursday. Aside from the potential for more lake snows, we are looking at a very cold period for much of next week. Cold cyclonic flow may contribute to the coldest temps we have seen this season which could mean highs only in the teens to mid 20s by Wednesday and Thursday. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... Bands of heavy lake effect snow will continue east of the lakes through the first half of tonight with local VLIFR conditions. After midnight winds will become northwest behind a trough crossing the lakes, forcing lake effect snow to become re-oriented southeast of the lakes with local IFR continuing through Friday. Outside of lake effect areas VFR will prevail. Looking at the individual TAF sites, KBUF and KIAG will see light snow showers developing toward Friday morning, with occasional light snow showers continuing through Friday. Conditions should be VFR to MVFR most of the time, although a few brief drops to IFR will be possible in any snow showers. KROC will be more significantly impacted, with lake effect snow developing after midnight and continuing through Friday morning with periods of IFR. The heaviest snow will likely move through between 07Z and 11Z. KJHW will be significantly impacted through the TAF period with IFR conditions most of the time. There will be a few periods of moderate to heavy snow tonight, and again later Friday afternoon. KART will miss most or all of the snow, with VFR prevailing. Outlook... Friday night through Saturday...IFR in lake effect snow southeast of the lakes. Occasional snow showers with more brief IFR elsewhere. Sunday and Monday...MVFR/IFR in widespread light snow. Tuesday...MVFR with a chance of snow showers. && .MARINE... High end small craft advisory conditions will continue right through Saturday on both lakes Erie and Ontario as low pressure moves very slowly east across Quebec, producing moderate to strong west to northwest winds on the Lower Great Lakes. Winds will be strongest on Lake Ontario, reaching a solid 30 knots tonight on the central and eastern waters. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Lake Effect Snow Warning until 6 AM EST Friday for NYZ007-008. Lake Effect Snow Warning until 6 AM EST Saturday for NYZ006- 012-019-020-085. Lake Effect Snow Warning from 1 AM Friday to 6 AM EST Saturday for NYZ004-005. Lake Effect Snow Advisory from 1 AM Friday to 6 AM EST Saturday for NYZ003. Lake Effect Snow Advisory until 10 AM EST Friday for NYZ021. MARINE...Small Craft Advisory until 7 PM EST Friday for LEZ040-041. Small Craft Advisory until 10 PM EST this evening for LEZ020. Small Craft Advisory until 7 AM EST Saturday for LOZ042>045. && $$ SYNOPSIS...HITCHCOCK/WCH NEAR TERM...HITCHCOCK/WCH SHORT TERM...APFFEL/TMA LONG TERM...SMITH AVIATION...HITCHCOCK MARINE...HITCHCOCK/WCH

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