Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 150304 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 1004 PM EST Thu Dec 14 2017 .SYNOPSIS... Low pressure will track into Michigan on Friday and then to New England Saturday. This will result in periods of lake effect snow during and below normal temperatures. High pressure will return to the region Saturday night and Sunday with fair weather. && .NEAR TERM /THROUGH FRIDAY/...
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High pressure will build across the Ohio Valley overnight...while a clipper low will move into Michigan. As a result winds will diminish by midnight, then gradually shift from the northwest to the southwest by morning. Although it will still be dry, the diminishing winds and a modest increase in moisture will allow lake effect snow to intensify a bit. Model consensus develops a convergent land breeze on both Lake Erie and Lake Ontario late tonight. This will result in more organized lake effect snows which may be enhanced by upstream moisture from Lake Huron. Model QPF is minimal, with the NAM forecasting hardly any measurable precipitation. Expect the steadiest snows to be focused near Oswego county where 3 to 6 inches is forecast. Off Lake Erie, expect 2 to 4 inches in Chautauqua and Southern Erie counties. In each case, the greatest amounts will be near the immediate shoreline due to the light winds. This is a difficult forecast since band intensity may vary given subtle differences in moisture and snow ratio. On Friday, winds will shift to the SSW as the clipper low moves closer. This will result in a brief burst of snow from Buffalo to Niagara Falls with 1-2 inches of snow possible Friday morning near the lakeshore. A similar story for the Watertown area off Lake Ontario. After this, bands will mainly impact Canada most of Friday afternoon. The exception is across western portions of Niagara county where a few inches of snow is likely depending on the exact location of the lake effect band. Otherwise, expect mainly dry weather outside of the lake effect bands. Otherwise, temperatures will continue to be below normal tonight with lows ranging from the single digits to mid teens. Highs on Friday will `warm` slightly into the 20s.
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&& .SHORT TERM /FRIDAY NIGHT THROUGH SUNDAY/... Friday evening will become very active again as another clipper passes by just north of Lake Ontario. The clipper will do little by itself, with just some light snow and less than an inch of accumulation outside of lake effect/lake enhanced areas. More importantly, this clipper will produce a much more favorable environment for heavy lake effect snow. The increased moisture, synoptic scale ascent, and fresh batch of cold air aloft will raise lake induced equilibrium levels to over 15K feet off both lakes near the time of the cold frontal passage. Deep moisture and a deep dendritic crystal growth zone will support favorable cloud microphysics. Convergence will max out as the cold front crosses each lake, and the frontal convergence combines with pre-existing convergence along bands of lake effect snow already over the lakes. These scenarios often produce a burst of very heavy snow with snowfall rates of over 2 inches per hour along with thunder and lightning, although they typically move quickly across the area as wind direction changes quickly with the cold frontal passage. Off Lake Erie... Late Friday afternoon a band of lake effect snow will be found across the Niagara Peninsula, extending across Grand Island and into Niagara County on SSW flow. As the front crosses the area, it will merge with the lake effect band and intensify it further, with the band moving fairly quickly south across the Buffalo Metro area. This may occur during the latter half of the Friday evening commute, and produce very poor travel conditions for an hour or two. By late evening the band of snow will move all the way into the western Southern Tier. It will initially still be strong when it first arrives in the Southern Tier, with snowfall rates then backing off overnight but still producing steady accumulations. The lake effect snow will remain across the western Southern Tier and possibly Southern Erie and Wyoming counties through Saturday morning, before increasing shear with the approach of a warm front disrupts the band. As far as accumulations go, expect 3-6 inches across portions of Northern Erie and Niagara counties, with much of that falling in just a 2 hour period during the early evening. Farther south, there will be an initial quick burst of heavy snow when the bands, followed by more persistent lake effect snow overnight into Saturday morning. This may produce totals of 6-10 inches in persistent bands, although there is some uncertainty on whether bands will be able to remain over one location long enough to reach warning criteria. With this in mind, we went with a Winter Storm Watch for lake effect snow east of Lake Erie for Friday evening through early Saturday afternoon. Off Lake Ontario... Late Friday afternoon a band of lake effect snow will be located on the Canadian side of the border near Kingston, Ontario in SSW flow. The front will arrive by late evening and merge with the lake effect band. This will carry an intensifying band of lake effect snow south and east across Jefferson County. This band will then further intensify as it moves into the Tug Hill region, with some of the mesoscale model guidance suggesting a short period of very high snowfall rates (3-4 inches per hour) for the Tug Hill during the wee hours of the morning Saturday. Given a very high cap and a relatively deep mixed phase layer, have added the LIKELIHOOD of thunder and lightning with this activity. This will especially be the case on the Tug Hill where higher terrain aids in the ability for cloud to ground strikes. On Saturday morning the band will move a little farther south into northern or central Oswego County and begin to weaken, with further weakening by midday as shear increases. As far as accumulations go, for central and northern Jefferson County accumulations will be limited by the fast band motion, with 2- 4 inches for Watertown and points north and east, although this may mostly fall in 2 hours. The band, and associated upslope flow will likely last longer across the Tug Hill Plateau. The longer residence time combined with potentially very high snowfall rates may produce 8-12 inches accumulation in persistent bands, centered on the Tug Hill. With this in mind, we went with a Winter Storm Watch for lake effect snow east of Lake Ontario for Friday evening through early Saturday afternoon. Once the lake effect snow diminishes Saturday, the 12Z model guidance has made some significant changes for Saturday. A trend that was first captured by the 06Z GFS and 00Z ECMWF is now shown by most model and ensemble guidance. The latest models show warm advection increasing rapidly across the central and eastern Great Lakes Saturday as a weak wave moves through the Midwest. This warm advection will spread abundant cloud cover, and possibly a streak of light snow across western and central NY during the day Saturday into Saturday evening. Given the big change from previous model guidance, just introduced a chance of snow showers for now, but if this trend continues, POPS will need to be increased. Saturday night and Sunday the warm front will continue to creep northeast across the region, with any remaining light snow ending as forcing along the frontal zone weakens. Sunday should remain dry, with the start of a modest warm up as temperatures rise into the mid 30s for the lower elevations of Western NY. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... For the start of next week, model solutions point to a deamplification of the pattern, as upstream blocking degrades. This will allow for a more progressive flow of Pacific influenced air across the Great Lakes region. Expect a warming trend from Sunday into Monday and Tuesday as upper-level ridging builds across the eastern Great Lakes. The thermal ridge axis transits the forecast area on Tuesday as the surface high slips to our east and next wave moves into the upper Great Lakes, which will push 850 mb temperatures briefly above the freezing mark Tuesday. Thus high temperatures slowly improve from the 20/30s on Sunday, to the 30s to near 40 on Monday, and right around 40 on Tuesday. Precipitation wise, a southern stream clipper along the warm front may produce some scattered showers Sunday night. The nearby retreating warm front boundary combined with weak wave passages in the progressive flow will then keep some scattered light shower chances in the forecast through Monday and Monday night. A stronger weather system will then plow a cold front across the region by Tuesday night, bringing both showers ahead of the front and lake effect snows and much cooler air behind the front for mid-week. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... Lake effect snow showers will consolidate into bands east of the lakes tonight...but this will only impact the KJHW Taf site. Winds will then shift to the southwest later tonight with lake snows lifting northward to BUF/IAG/ART by Friday morning. This will result in a few hours of IFR or lower conditions. SSW winds will push lake snows mainly north and west of all TAF locations Friday afternoon, with the exception of IAG which will be close to these snow bands. Outlook... Friday night...VFR with IFR in lake effect snow. Expect a few hours of heavy snow at BUF/IAG/ART Friday evening, then lake effect should move to the south. Saturday...Mainly VFR. Lake effect snow showers mainly away from TAF sites. Saturday night and Sunday...VFR. Sunday night through Tuesday...VFR/MVFR with a chance of snow showers. && .MARINE... Small craft advisory conditions will remain in place for the Lake Ontario nearshore waters through the first half of tonight...then a weakening surface pressure gradient will allow winds and waves to subside. While relatively light winds will be in place late tonight and early Friday across the Lower Great Lakes...an approaching area of low pressure will encourage winds to freshen Friday afternoon and evening. The increase in winds will be accompanied by renewed lake snows...which will be heavy on Lake Erie and on the east end of Lake Ontario. && .BUF WATCHES/WARNINGS/ADVISORIES...
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NY...Lake Effect Snow Warning from 10 PM Friday to 10 AM EST Saturday for NYZ007. Winter Weather Advisory until 7 AM EST Friday for NYZ006. Lake Effect Snow Warning from 10 PM Friday to 1 PM EST Saturday for NYZ006-008. Winter Weather Advisory from 11 AM to 10 PM EST Friday for NYZ001. Winter Storm Watch from Friday evening through Saturday afternoon for NYZ012-019-020-085. Winter Weather Advisory from 4 PM Friday to 1 AM EST Saturday for NYZ010. MARINE...Small Craft Advisory until 7 AM EST Friday for LOZ043>045. Small Craft Advisory until 1 AM EST Friday for LOZ042.
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&& $$ SYNOPSIS...APFFEL NEAR TERM...APFFEL/RSH SHORT TERM...HITCHCOCK/RSH LONG TERM...CHURCH AVIATION...APFFEL/RSH MARINE...RSH

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