Area Forecast Discussion
Issued by NWS Buffalo, NY

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000 FXUS61 KBUF 211118 AFDBUF Area Forecast Discussion National Weather Service Buffalo NY 618 AM EST Mon Jan 21 2019 .SYNOPSIS... A northwesterly flow of bitterly cold air will result in dangerously low wind chill values today, and another very cold night tonight. The arctic airmass will finally move out of the area on Tuesday, and this will be followed by low pressure which will track to our north on Wednesday. This will result in a short period of above normal temperatures along with some mixed precipitation mid-week. && .NEAR TERM /THROUGH TONIGHT/... Bitterly cold conditions will prevail throughout the period. Temperatures will be below zero in most locations through mid- morning. This combined with winds gusting to 30 mph in spots will result in wind chills of 20 to 30 below in most areas, with 30 to 40 below zero across the North Country and interior portions of the Southern Tier through this morning. Temperatures will only rise into the single digits this afternoon, except across the North Country where temperatures will remain below zero. This will result in a modest improvement, but still bitterly cold conditions this afternoon. Consequently, Wind Chill Advisories and Warnings remain in effect for this potentially life threatening risk. Meanwhile, lake effect snow continues this morning southeast of Lake Ontario, and to a lesser extent Lake Erie. These extend roughly 15 miles inland from the lakes, but vary in intensity with numerous narrow tendrils embedded within. It`s also worth noting that these are developing below a low capping inversion of 3-5 kft so radar will not effectively sample this far away since the beam will overshoot the snow. However, webcams and satellite imagery confirm fairly persistent snows southeast of Lake Ontario, and to a lesser off Lake Erie. Since we have effectively lost our dendritic growth zone in this arctic airmass, snowfall rates from the resulting plates and columns will be under a half inch hour. However, these are effective in lowering visibility, and persistence still could bring another 1 to 3 inches of snow today south of Lake Ontario. There also could be areas of blowing snow. A Winter Weather Advisory remains in effect for counties adjacent to and south of Lake Ontario. Most of the snow accumulation will occur thorugh this morning before the upper level trough and the core of coldest air aloft moves east into New England. Surface high pressure centered across Ohio this evening will build eastward across our region tonight. Winds will maintain longest east of Lake Ontario, where wind chill headlines may have to be extended. Wind chills aside, it will be another very cold night. Although temperatures aloft will be considerably warmer, the surface high will provide conditions favorable for radiational cooling. Temperatures will again fall below zero in most locations, except along the immediate lakeshores. Lows should run 10 to 20 below across the North Country, with even colder readings possibly in some spots. Otherwise, leftover lake snow showers southeast of Lake Ontario should taper off to flurries while the remainder will experience mainly clear skies. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... Tuesday will start very cold with a +2 SD surface high pressure centered over the region. This surface high will slide to the mid- Atlantic coastline through the day and a southerly flow will commence a moderating temperature trend. Tuesday night surface low pressure in the base of a mid level trough will advance from the midwest to the central Great Lakes. A strong LLJ will develop ahead of this low pressure, and this jet will aid in rising temperatures through the night and bringing above freezing temperatures to the region late Tuesday night and into Wednesday. Precipitation wise, an initial broken area of light snow is possible late Tuesday night on the leading edge of the LLJ. The precipitation is then expected to become more widespread towards daybreak across far WNY and the Saint Lawrence Valley as moisture deepens and the surface low draws closer to our region. This precipitation will then spread over the Genesee Valley and Finger Lakes region Wednesday. This LLJ will bulge a layer of much warmer air aloft across WNY (850 hPa +2 to +5C) while surface temperatures around freezing lag behind. A wintry mix is expected, with snow transitioning to sleet/freezing rain as we warm aloft, and then plain rain briefly spreading across WNY as surface temperatures warm into the upper 30s to lower 40s. Cooler air to the north may linger the precipitation as all snow across the North Country. Here there is potential for 2 to 4 inches of snow accumulation by Wednesday evening. There is still uncertainty as to how fast and how much we warm aloft...but for now will mention the risk of freezing rain in the HWO for WNY. Of note, the recent extreme cold spell and prospects of untreated roads may elevate the freezing rain potential...with freezing rain on frozen ground surfaces that will lag behind in warming. By Wednesday night the surface low cutting to the north of Lake Ontario will push a cold front across our region, changing the plain rain back to all snow. This front will slowly move across our region as a wave of low pressure will likely form on the front in the South. As this wave rides northward, precipitation associated with it may brush by our eastern zones. Snow accumulation behind the front will be little to none for the lower terrain, however higher terrain to the east of both lakes may receive a few inches oweing to lake enhancement and upslope effects. && .LONG TERM /THURSDAY THROUGH SUNDAY/... The pattern will turn much more wintry again for the end of the week and next weekend after our brief warm-up on Wednesday. The +PNA pattern will re-amplify significantly by next weekend across the North American continent, with a deep trough carving out in the east. This will push temperatures to well below average again. This cold pattern will have staying power, with long range outlooks and ensembles suggesting it lasting through the end of the month and beyond. Looking at the details, on Thursday a complex frontal zone will advance to the east coast. A wave of low pressure will be running northeast along the boundary, and associated ascent from this wave and the approaching mid level shortwave will likely allow precipitation to linger on the cold side of the boundary. By Thursday morning all areas should be back to snow, with some minor accumulations possible. The synoptic snow will taper off from west to east through the day, with some minor lake effect snow showers possible later Thursday afternoon and Thursday night southeast of the lakes as colder air aloft arrives. High temperatures Thursday will be in the lower 30s in most locations, and lows Thursday night will be in the upper teens to lower 20s. Late Thursday night and Friday a strong mid level trough and associated surface low/cold front will cross the region, marking the leading edge of the return to much colder temperatures. This system will bring a chance of snow showers areawide, with potential for lake enhancement east of the lakes. The cold becomes well established by the weekend. Model guidance begins to diverge with the handling of clipper shortwaves moving through the mean longwave trough, but in a general sense one or two weak systems will continue to support light snow chances through the weekend. There may also be lake effect potential next weekend, although given the model differences with the handling of the clipper systems there is a good deal of uncertainty with respect to placement and strength. High temperatures by the weekend will be back into the teens in most locations, with lows in the single digits, and below zero east of Lake Ontario. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... A northwesterly flow of bitterly cold air will continue to generate countless bands of light lake effect snow southeast of Lakes Erie and Ontario through this morning. Although snow accumulation will be light, the very small snowflakes will be very effective in lowering visibility. Conditions will vary anywhere from MVFR to LIFR in and out of these bands during this time. The most persistent snows will be at KIAG/KROC/KJHW. Conditions will improve this afternoon as drier air moves in and winds diminish. MVFR cigs will gradually dissipate with mainly VFR conditions expected by this evening. High pressure will build across the area late tonight with VFR flight conditions. Outlook... Tuesday...VFR. Tuesday night and Wednesday...MVFR/IFR in snow changing to mainly rain. Thursday...VFR to MVFR with scattered snow showers. Friday...VFR to MVFR in scattered to numerous snow showers... with IFR possible in more numerous snow showers east of the lakes. && .MARINE... A relatively tight surface pressure gradient will remain in place over the Lower Great Lakes through this evening. Winds will diminish from west to east starting this afternoon as high pressure builds in from Ohio. This will keep Small Craft Advisory conditions in place throughout the Lower Great Lakes...with enough wave action to continue to support the Heavy Freezing Spray Warning. The area of high pressure will drift across the Lower Great Lakes tonight. This will allow winds, waves, and any lingering freezing spray to diminish. Light winds will then gradually freshen over the lakes during the day Tuesday, as the large surface high will move east into New England. && .BUF WATCHES/WARNINGS/ADVISORIES... NY...Wind Chill Warning until 7 PM EST this evening for NYZ006>008- 012>014-019>021-085. Winter Weather Advisory until 11 AM EST this morning for NYZ001>006. Wind Chill Advisory until 7 PM EST this evening for NYZ001>005- 010-011. MARINE...Heavy Freezing Spray Warning until 10 AM EST this morning for LEZ040-041. Small Craft Advisory until 1 PM EST this afternoon for LEZ040-041. Small Craft Advisory until 10 AM EST this morning for LOZ030. Heavy Freezing Spray Warning until 6 PM EST this evening for LOZ042>045-062>065. Small Craft Advisory until 1 AM EST Tuesday for LOZ042>044. Small Craft Advisory until 7 PM EST this evening for LOZ045. && $$ SYNOPSIS...Apffel NEAR TERM...Apffel SHORT TERM...Thomas LONG TERM...Hitchcock AVIATION...Apffel MARINE...Apffel

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