Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 181345 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 845 AM EST Sat Jan 18 2020 .SYNOPSIS... A strengthening storm system will pass to our west late today and the first half of tonight...then it will transition to the New England late tonight and Sunday. This will result in a prolonged period of potentially impactful weather that will range from accumulating mixed precipitation and strong wind gusts...to lake snows that will total over a foot in the lake snow belts. The effects from this widespread event may be minimized by its weekend timing. Some lake snow showers and a short lived period of very cold weather will follow on Monday to close out the holiday weekend. && .NEAR TERM /THROUGH SUNDAY/... ...A Complex Storm will Support Widespread Winter Weather Headlines through Sunday... A broad area of low pressure was centered over Wisconsin at daybreak this morning. While the main supporting shortwave can be seen in WV imagery over Minnesota...the driving feature for this evolving system will be a robust shortwave that is depicted over Missouri. As this bundle of energy rounds the base of the longwave trough and makes its way across the Ohio Valley this afternoon...it will promote intensification of the surface low that will be moving across Lake Michigan. Initially...a divergent upper level flow ahead of the consolidating sfc low will provide lift for increasingly widespread pcpn that will START as a mix of sleet and snow over the far western areas. Sites east of Buffalo should have a longer period of light snow before the change over. As we work our way into the midday/afternoon...a strengthening H25 jet (150kts) will push from the Ohio Valley across the Appalachians. This will place us under the favored left front exit region for enhanced lift...while a deepening southerly flow will impinge upon the first of two warm frontal boundaries that will be advancing from the Upper Ohio Valley to the Lower Great Lakes. The resulting frontogenetic lift will increase the intensity of the pcpn... while thermal profiles will gradually `warm` below cloud level. Climatologically...a deepening storm system cutting by to our west would normally guarantee a change over from snow to at LEAST a mix...if not to just rain at some point. Interestingly...the vast majority of the guidance packages have struggled with depicting a significant warm nose as the deepening sfc low nears our region. Will have to continue to blend climatology with some of the `warmer` guidance (3:1 as the models look woefully too cold)...with the result being a more pronounced transition to mixed pcpn over the western counties all the way to the south shores of Lake Ontario by this evening. The change to a mix...and for some sites (esp near Lk Erie) to a few hours of plain rain...will severely cut into snowfall amounts into early tonight...which will generally range from 1 to 3 inches over most areas. Pcpn east of Lake Ontario is expected to remain as all snow though this event. The primary sfc low will reach its peak intensity (lowest sfc pres) this evening...then as it becomes `captured` by its supporting upper low...the newly stacked mature system will slowly start to weaken as it will move by to our north. This will effectively shut down the moderately strong warm advection that had been in place over our forecast area...as an elevated triple point will cross our forecast area. This will allow the pcpn to start change back over to all snow over the western counties. During the wee...pre dawn hours of Sunday morning...the cold air on the backside of the evolving complex storm system will deepen to the point where the lake snow machines will fire up on Lake Erie. The 250-260 flow will initially direct 1 to 3 inches moderately heavy lake snow across the southern half of Erie county...possibly starting over the Buffalo `Southtowns`. As we work past daybreak Sunday...the steering flow will veer to 270 and the concentrated lake snows will push south across the Southern Tier. Meanwhile...a cap that had been in the vcnty of 6k ft will rise to nearly 10k ft. The deeper convection and subsequent deeper dendritic growth zone (DGZ) will encourage more efficient snow making with snowfall rates of 1 to as much as 2 inches an hour generating daytime snowfall of 4 to 7 inches. The current lake effect snow watch for this area will likely be upgraded to a warning in an upcoming package. Meanwhile across the Eastern Lake Ontario region...strong frontogenetic forcing Saturday night will produce 4 to 7 inches of synoptic snow. This snow could be moderately heavy at times Saturday night...but as the synoptic storm system weakens during its transition to the coast...the widespread snow will lighten in intensity through the first half of Sunday. Once the new coastal storm take shape...strong cold advection during the midday and afternoon will finally initiate lake snows over that region. An initial 260 flow early in the afternoon will fairly quickly veer to more than 300 deg by nightfall. While the organizing lake snows will be push south during this timeframe...daytime accumulations could top 8 inches on the Tug Hill. Will thus maintain the winter storm warning for this area...which will cover not only the synoptic snow today and tonight...but the lake snows on Sunday. Finally...it will become quite windy across the region. A fairly strong cold front will plow across the region this evening. A 60- 65kt LLJ in the vcnty of this boundary will at least partially mix to the sfc. This powerful LLJ will weaken fairly quickly by 6z though as the main system transitions to the coast. Will have to closely monitor this aspect to the weekend storm...as there is possibility that damaging winds could once again develop for a brief period over the western counties. For now...will maintain wind gusts to 45 to 50 mph...especially west of the Genesee valley. Relatively strong winds will persist across the forecast area through Sunday...as a 40kt LLJ within strong cold advection will support sfc gusts of more than 30 mph. This will lend to areas of wind blown snow...mainly in the lake effect areas. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... A west to east oriented shortwave trough will drop south from Ontario and cross the area Sunday evening. This trough will cause an increase in coverage for snow across the region as moisture and forcing associated with the trough brings a batch of snow showers south with it. Behind this trough, winds will shift slightly more northerly and cold air advection will continue. 850H temperatures will hold fairly steady around -15C from Sunday night through most of Monday. These temps will support a continued lake response through the period. As the trough drops south through late Sunday night, lake enhanced snow with the trough will transition to lake effect. Moisture associated with the trough will decrease as the trough moves farther south and out of the area, but low level moisture downwind of the lakes will help continue the lake response through most of the day on Monday. Equilibrium heights will slowly lower through the night Sunday into Monday morning as the trough drops south of the area. Between lowering equilibrium heights and decreasing moisture, snow off the lakes should be lighter than earlier on Sunday. Snowfall amounts Sunday night between the synoptic snow from the trough and from lake enhancement turning to lake effect, should be around 2 to 4 inches south of Lake Ontario where a lake response is strongest off of both lakes, and around 1 to 2 inches where snow is primarily in the synoptic form from the trough. With a continued fairly tight pressure gradient behind the earlier low, winds will still be somewhat strong enough to generate areas of blowing snow through the night on Sunday. Temperatures Sunday night will be in the low to mid teens south of Lake Ontario, and near 0 for areas east of Lake Ontario. Monday will see a continued lake response as low level moisture downstream of the lakes continues within a west to northwest flow regime and 850H temps still around -15C. Snowfall should continue to be light for most areas. Snowfall for areas that will see the best lake response continue can expect around 1 to 2 inches for the day on Monday with all other areas having and inch or less of accumulation. Temperatures on Monday will be in the upper teens to low 20s south of Lake Ontario and in the mid to upper teens east of Lake Ontario. Monday night, lake snows southeast of the lakes will continue to slowly taper off, with likely POPs early in the night transitioning to chance POPs by Tuesday morning. A large area of high pressure will center over the mid Mississippi Valley by Tuesday morning, causing a slow increase in ridging across the region. Areas southeast of the lakes can expect up to an inch of snowfall with most other areas only picking up a coating to a half inch of snow. Temperatures Monday night will be in the low teens south of Lake Ontario and from around -5C to 0C for the North Country. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Tuesday into Tuesday night, lake effect snow showers will diminish through the day into the night. Increased ridging across the region as an area of high pressure centers over the Ohio Valley will continue to cut down on the lake response. Warm air advection on Tuesday will warm temperatures to above -10C by the evening on Tuesday, further supporting a weakening lake response. The large area of high pressure will center over the Delmarva Peninsula by Thursday afternoon. This will result in dry conditions across the region and will provide a southerly flow that will start to increase temperatures through late in the week. Temperatures for this period start out around 5 to 10 degrees below normal on Tuesday, and with day to day warming end with temperatures that are around 5 to 10 degrees above normal on Friday. && .AVIATION /14Z SATURDAY THROUGH WEDNESDAY/... Conditions will deteriorate to mainly MVFR cigs and mainly IFR vsby today from west to east as snow and wintry mix (western NY) will work across the region. Though similar flying conditions will persist into tonight, the wintry mix of rain/snow may expand across much of the area during the evening (does stay all snow at ART though), before changing back to snow and blowing snow late tonight. Gusty southwest winds to 40 kts are expected tonight with the strongest at IAG, BUF and ROC. Outlook... Sunday through Tuesday...MVFR/IFR due to lake effect snows and blowing snow east of the lakes. Wednesday...MVFR improving to VFR as lake effect snows peter out. && .MARINE... A moderately strong area of low pressure will pass just north of Lakes Erie and Ontario this afternoon and tonight. The passage of the low is favorable for the development of gales on Lakes Erie and Ontario from tonight through early Sunday morning, with sustained winds peaking at or just over 35 knots on both lakes. This will be a relatively short gale, with winds diminishing through the day Sunday and becoming more northwest. && .TIDES/COASTAL FLOODING... Strong winds developing tonight into Sunday will bring another round of lakeshore flooding to Lake Ontario. The combination of high lake levels, strong onshore westerly winds, and high waves will produce some lakeshore flooding in bays and inlets at the east end of Lake Ontario impacting lakeshore areas of Jefferson and Oswego counties. A seiche will also develop on Lake Erie tonight through Sunday morning as winds rapidly become southwest and increase to gale force. This will produce minor flooding in bays and inlets, and other low lying areas along the shoreline. Water may spray across Route 5 in Hamburg. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Winter Weather Advisory until 1 AM EST Sunday for NYZ012-019- 020-085. Lakeshore Flood Advisory from 7 PM this evening to 10 AM EST Sunday for NYZ010-019-085. Winter Storm Watch from late tonight through Monday morning for NYZ012-019-020-085. Lakeshore Flood Warning from 4 AM to 1 PM EST Sunday for NYZ006-007. Winter Storm Warning from 1 PM this afternoon to 1 AM EST Monday for NYZ006>008. Winter Weather Advisory until 10 PM EST this evening for NYZ004-005. Winter Weather Advisory until 9 AM EST Sunday for NYZ001>003- 010-011. Winter Weather Advisory until 10 PM EST this evening for NYZ013-014-021. MARINE...Small Craft Advisory from 3 PM this afternoon to 4 PM EST Sunday for LEZ020. Small Craft Advisory until 6 PM EST this evening for LEZ040-041. Gale Warning from 6 PM this evening to 10 AM EST Sunday for LEZ040-041. Small Craft Advisory from 3 PM this afternoon to 4 PM EST Sunday for LOZ030. Gale Warning from 2 AM to 10 AM EST Sunday for LOZ043>045- 063>065. Gale Warning from 11 PM this evening to 10 AM EST Sunday for LOZ042-062. && $$ SYNOPSIS...RSH NEAR TERM...RSH SHORT TERM...SW LONG TERM...SW AVIATION...RSH/TMA MARINE...Hitchcock/TMA TIDES/COASTAL FLOODING...Hitchcock/TMA

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