Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 201452 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 952 AM EST Tue Nov 20 2018 .SYNOPSIS... A weak clipper will produce some light snow across the region today with minor accumulations mainly across the higher terrain east of the lakes. A stronger clipper will move through the region late tonight and Wednesday, producing more widespread snow showers and a period of briefly heavy lake effect snow east and northeast of the lakes. A few lake effect snow showers will continue southeast of the lakes Wednesday night. Near record cold is expected for Thanksgiving Day before a warming trend arrives by the weekend. && .NEAR TERM /THROUGH WEDNESDAY/... As of 950 am...the axis of a mid level shortwave and its associated weak surface cold front has pushed into far western New York...with light snow shower activity becoming increasingly widespread across the region from west to east. This system will push eastward across the rest of the region through early to mid afternoon...with the attendant light snow showers lasting through about midday across western New York...and through about mid afternoon east of Lake Ontario. The best coverage will be east of the lakes where some very modest lake enhancement will occur and may allow for 1-2 inches of accumulation across the higher terrain east of Lakes Erie and Ontario today, with less than an inch falling elsewhere. The majority of the snow will taper off and end from west to east this afternoon. Some very limited lake effect snow may continue into this evening near the southeast corner of Lake Ontario, but any accumulations with this will be very light with diminishing moisture and lowering inversion heights. Highs today will reach the lower to mid 30s in most areas by late morning or midday...before temperatures pull back a few degrees during the afternoon as cold advection begins. A weak surface ridge will briefly cross the eastern Great Lakes this evening, with most areas dry. The one exception may be southeast of Lake Ontario, where some limited/light lake effect snow may continue from eastern Wayne to Oswego counties. Late tonight and Wednesday our attention turns to a much stronger clipper that will pass by just north of the lakes. Stronger large scale ascent and much stronger low level convergence just ahead of an arctic front will produce a more robust lake response, with lake induced equilibrium levels rising to 8-10K feet just ahead of the arctic boundary. From a synoptic standpoint, the clipper will produce a few snow showers with a coating to an inch of accumulation outside of lake effect areas. Winds and Temperatures... It will become quite windy on Wednesday with a sharp pressure gradient, cold advection, and steepening lapse rates promoting downward momentum transfer. Expect gusts of 30-35 knots in the typically windier lake plain locations, and 25-30 knots farther inland. This will produce blowing and drifting snow in areas which receive accumulating snow. Highs will be in the low to mid 30s briefly Wednesday morning. Strong cold advection will then force temperatures to drop through the 20s in the afternoon, with wind chills dropping into the teens. Now for the lake effect... Off Lake Erie... Expect a band of snow to develop rapidly after 06Z over the lake and extend northeast into the Buffalo Metro area. This band may briefly brush southern Niagara and Orleans counties as well before settling south across the Buffalo Metro area and Genesee County, intensifying as it moves south. The snow will not last in any one location for more than a few hours, but may produce 1-2 inch per hour rates for a brief time. The northeast end of the band may briefly reach Monroe County as well with minor accumulations in the western suburbs of Rochester. The band should be just south of Buffalo and Batavia by 12Z Wed, then push bodily onshore and focus heavy snow on the Chautauqua Ridge for a few hours early Wednesday morning as it becomes captured by the arctic front. After late morning, expect transient bands of snow to focus on the western Southern Tier, with any upstream connection to Lake Huron ending up in NW PA or NE OH by late in the day. The fast band motion will limit accumulation potential somewhat, but if the band becomes strong enough it may drop a quick 2-4 or 3-5 inches from the Buffalo Metro area and western Genesee County southward across the higher terrain. In addition, rapidly increasing winds will produce plenty of blowing and drifting snow and poor visibility. Off Lake Ontario... Expect a similar evolution a few hours later. A weak band of lake effect snow may drift north across the Tug Hill region through the middle of the night. This will then intensify across central Jefferson County including Watertown by early Wednesday morning. This band of snow will then move fairly quickly south across the Tug Hill region through the late morning hours and cross Oswego County early afternoon. Snowfall rates may briefly reach 1-2 inches per hour in this band. During the mid to late afternoon a somewhat weaker band of lake effect snow will move onshore from Orleans/Monroe counties to portions of Wayne and Cayuga counties as boundary layer flow veers quickly to the northwest. Mesoscale model guidance suggests it may develop an upstream connection to Georgian Bay during this time frame, although the steadily veering boundary layer flow should keep the band moving enough to keep accumulations somewhat in check along the south shore of Lake Ontario. The fast band motion will limit accumulation potential somewhat, but if the band becomes strong enough it may drop a quick 2-4 or 3-5 inches from central Jefferson County including Watertown, southward across the Tug Hill region. Expect 1-2 inches later in the afternoon from western Oswego County westward along the south shore of the lake to Orleans County, including the Rochester area. There will be some additional accumulations in this area Wednesday night. In addition, rapidly increasing winds will produce plenty of blowing and drifting snow and poor visibility. && .SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY/... Wednesday night through Thursday night will likely bring the coldest temperatures of the season. Wednesday night temperatures will bottom out around the low to mid teens for areas near the lakes, and in the single digits to near zero across the higher terrain. Temperatures on Wednesday night and Thursday will likely be the coldest temperatures that most areas experience since this past March or February. As the area of Arctic high pressure moves into the northern Great Lakes, behind a departing upper level trough, cold air advection that began on Wednesday will continue through Wednesday night. The Arctic high will be centered over WNY by Thursday evening. 850Ts on Wednesday night will bottom out around -20C from WNY to near -22C over N.C.NY. If these 850Ts come to fruition, it will be in the top five coldest 850Ts recorded in the month of November for the Buffalo sounding location. The coldest 850 temperature per NWS archive was -21C on November 21, 1987, with that number in jeopardy of getting eclipsed on Thursday morning. Light lake effect snow will continue from earlier on Wednesday through early Thursday morning. Lake effect snow that does persist through the night should taper off through the early morning on Thursday. Moisture levels will drop overnight Wednesday as the Arctic high approaches the area on Thursday, with the GFS and NAM showing PWATs of around a tenth of an inch. The Euro though does show some slightly better moisture content. With 850Ts this cold, any moisture that will be present will likely be in the snow growth zone. Likely POPs will continue very early on this period as the lake effect snow starts to wind down. With the above in mind, will trend POPs down to chance for lake effect southeast of the lakes through the early morning before sunrise. As ridging increases with the approaching high, resulting in increasing subsidence POPs will continue to lower after sunrise. Any continued lake effect snow showers will continue to decrease in coverage through the mid morning on Thursday. Snow accumulations from the lake effect snow should remain below an inch overnight Wednesday night, with most of that falling early in the period. High temperatures on Thursday will be in the teens east of Lake Ontario, and in the upper teens to low 20s across the rest of the area. High temperatures on Thursday will be around 25 degrees below normal. Rochester and Buffalo could experience their top 5 coldest Thanksgivings on record. Thursday night into Friday will start out with continued cold temperatures from the Arctic high over the area, but some warmer temperatures will build into the area as the high shifts to the east and a southerly flow establishes starting Friday morning. Lows on Thursday night and Friday morning will be chilly once again with temperatures in the single digits to near zero in the higher terrain and in the low to mid teens closer to the lakes. Those who plan to venture out shopping Thursday night and Friday morning should dress appropriately for the cold conditions. Friday high temperatures will be in the mid to upper 30s near the lakes, and in the upper 20s to low 30s across the higher terrain. The area should experience mostly cloud free conditions for most of the day, with some clouds increasing in the late afternoon and evening ahead of the next chance for precip starting overnight Friday night. && .LONG TERM /FRIDAY NIGHT THROUGH MONDAY/... The weekend continues to look unsettled with precipitation chances increasing, but with milder temperatures. Upper level trough will move slowly across the Great Lakes into the Northeast Conus, eventually becoming negatively titled over the area. Surface low over the Carolinas will eventually push toward New York and New England. Expecting mainly rain for precipitation type, but cannot rule out pockets of mixed precipitation during the cooler overnight and early morning periods. Highs should be mainly in the 40s over the weekend, with overnight lows in the 30s. A large area of low pressure will approach the area from the Ohio Valley on Monday, with increasing chances for rain through the day. Temperatures for Monday will once be in the low to mid 40s across the area. && .AVIATION /15Z TUESDAY THROUGH SATURDAY/... A mid level trough and surface cold front will move across the area this morning and produce areas of snow showers. The best coverage of the snow showers will be east and northeast of the lakes as some modest lake enhancement develops. This will produce several hours of IFR VSBY and MVFR CIGS at most of the TAF sites, with some IFR CIGS across the higher terrain. Conditions will improve from west to east this afternoon as the system exits the area, with VSBY returning to VFR and CIGS a mix of MVFR and VFR. Some very limited lake effect snow may continue into this evening near the southeast corner of Lake Ontario with local IFR. Another, stronger mid level trough and cold front will approach the area late tonight. This will bring an increasing chance of snow showers after 06Z Wed, with lake effect snow also developing initially northeast of the lakes. This heavier lake effect snow may impact KBUF for a few hours late tonight with conditions near or below airfield minimums possible. Heavier lake effect snow will develop near KART shortly before 12Z Wed. Outlook... Wednesday...areas of MVFR/IFR in periods of snow showers and lake effect snow. Thursday and Friday...VFR. Saturday...MVFR or IFR as a system moves into or south of the region with rain. && .MARINE... A cold front will finish crossing the Lower Great Lakes today, with west-northwesterly winds increasing from west to east behind the front through this afternoon. This will produce Small Craft Advisory-worthy conditions that will last through tonight. A stronger cold front will then cross the eastern Great Lakes Wednesday. Latest guidance is a bit stronger, and may result in a period of Gales on Lake Ontario with high end Small Craft Advisory conditions on Lake Erie. A Gale Watch remains in effect for Lake Ontario. The wind will last through Wednesday night before high pressure builds into the eastern Great Lakes Thursday with diminishing winds. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Winter Weather Advisory from 4 AM to 4 PM EST Wednesday for NYZ007-008-019-020. Winter Weather Advisory from 7 AM to 7 PM EST Wednesday for NYZ006. Winter Weather Advisory from 1 AM to 10 AM EST Wednesday for NYZ010-011. Winter Weather Advisory from 4 AM to 1 PM EST Wednesday for NYZ012-085. MARINE...Small Craft Advisory from 3 PM this afternoon to 1 AM EST Thursday for LEZ040-041. Small Craft Advisory from 2 AM to 7 PM EST Wednesday for LEZ020. Gale Watch from Wednesday morning through Wednesday evening for LOZ043>045-063>065. Gale Watch from Wednesday morning through Wednesday evening for LOZ042-062. Small Craft Advisory from 1 PM this afternoon to 10 AM EST Wednesday for LOZ043-044. Small Craft Advisory until 7 AM EST Wednesday for LOZ042. Small Craft Advisory from 6 PM this evening to 10 AM EST Wednesday for LOZ045. && $$ SYNOPSIS...Hitchcock NEAR TERM...Hitchcock/JJR SHORT TERM...SW LONG TERM...SW/TMA AVIATION...Hitchcock MARINE...Hitchcock/JJR

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