textproduct: Cleveland

WHAT HAS CHANGED

Lucas and Wood Counties have been upgraded to a Winter Storm Warning since confidence has sufficiently increased for greater than 6 inches of snow in far NW Ohio. The onset of the snow has trended a few hours slower tonight, especially in NE Ohio and NW PA where snow will not begin until after 1 AM Sunday. Temperatures next week are trending colder, with below zero air temperatures Monday night and Thursday night and daily highs struggling to rise past the low to mid teens.

KEY MESSAGES

1) The major winter storm remains on track to impact all of northern Ohio and NW PA tonight into Monday bringing widespread snow, sub-zero wind chills, and treacherous travel.

2) Temperatures will fall below zero again in the wake of the storm Monday night into Tuesday morning, with dangerous wind chills of -15 to -20 creating significant cold exposure risks.

3) Very cold conditions will continue all of next week with bouts of at least light snow. The prolonged cold will elevate risks for cold exposure and damage to infrastructure.

DISCUSSION

KEY MESSAGE 1... Other than the bitter cold arctic air, conditions are quiet across the region this morning ahead of the major winter storm set to impact the region. Temperatures range from about 0 to 12 below zero, with the coldest readings in far eastern Ohio and interior NW PA. Winds will continue to diminish through sunrise as the arctic high builds overhead, so the Cold Weather Advisory should be able to expire at 12Z.

Now for the winter storm, infrared satellite and water vapor loops early this morning show an active southern stream subtropical jet extending from Mexico through the southern Plains and Mid Mississippi Valley ahead of a closed mid/upper low drifting onshore of Baja California. This is the beginning stages of the storm, with this subtropical jet pumping mid-level moisture into the southern Plains and Mid Mississippi Valley. As the closed low progresses across Mexico and into Texas today through tonight, it will phase with a strong northern stream mid/upper shortwave dropping through the Rockies and northern Plains. In response to this phasing, surface cyclogenesis will take place along the Texas and Louisiana Gulf coasts this evening, with a coupled mid/upper jet structure aiding in a deepening surface low lifting into the eastern Tennessee Valley by Sunday morning and across the Lower Ohio Valley and central Appalachians Sunday evening. A sharp and rapidly deepening mid/upper longwave trough axis swinging through much of the eastern CONUS behind the storm Monday will allow the inland low to transfer to a strengthening coastal low near the Jersey shore as the system bombs out off the New England coast by Monday night.

Precipitation will rapidly expand across the southern Plains and Mid Mississippi Valley today as the phasing mid/upper jet dynamics lead to a strengthening low-level jet and resultant moisture advection and isentropic ascent from an open Gulf. With such a strong 1040-1050 mb arctic high anchored across the Great Lakes ahead of this system, this will set up a classic overrunning situation. The broadening area of warm/moist advection and isentropic ascent overtop of the low-level arctic air supports a massive shield of wintry precip that will approach our region from the southwest. Timing has slowed in all guidance regarding the onset of snow tonight across northern Ohio and NW PA. This is both due to model guidance obtaining a better handle on the aforementioned phasing, which typically slows down systems, as well as abundant amounts of low-level dry air from the arctic high making initial precip fall as virga. Snow will probably not begin in NW Ohio until after 03Z, but the delay will be more noticeable in NE Ohio and NW PA where the onset of snow will probably be more like 06 to 07Z. Nevertheless, kept all headlines starting at 00Z since the overall message remains the same that snow will develop tonight with deteriorating visibility and road conditions. Once the snow begins, it will continue steadily through Sunday night before tapering off from west to east Monday morning into the afternoon. Lake enhancement and upslope flow in NE Ohio and NW PA will linger the snow the longest into Monday afternoon.

In terms of snow amounts, the heaviest snow is still expected to fall Sunday and Sunday night as the low tracks across the Lower Ohio Valley and central Appalachians, with the greatest synoptic support and moisture advection in a broad deformation zone on the NW flank of the low across our region during that time. The aforementioned coupled jet structure will set up strong mid-level frontogenetic forcing, and it is within that band that the heaviest snowfall rates are expected. The entire swath of snow across the region will easily put down 4 to 8 inches of snow areawide given the cold temps and dry snow (greater than 20:1 ratios), but locations beneath the best frontogenesis band will see the highest amounts of 10-12 inches (locally higher possible). Weak mid-level instability within that band could also result in convective snow bursts with rates over 1 inch per hour. New guidance overnight has not changed much in terms of thinking, with the greatest probabilities for the heaviest snow still expected along a Mt. Vernon to Youngstown and Meadville line. This is reflected in probabilistic data for snowfall amounts of greater than 8 inches in 24 hours. Those probabilities are around 25% in far NW Ohio near Toledo to 85 to 90% along the Mt. Vernon to Youngstown line. Despite much lower probabilities for far NW Ohio, upgraded that area to a Warning since the dry snow ratios will probably allow amounts to overachieve a bit, with at least 6 to 7 inches expected. Overall, the entire area should see at least 4-8 inches between late Saturday night and Monday afternoon, with 6-10 inches most likely along and east of I-71. Areas with the greatest risk of seeing over 12 inches will be that Mt. Vernon to Youngstown and Meadville line. The one caveat is lake enhancement Monday morning into the afternoon as the system pulls away. Lake Erie is mostly ice covered, but there will be a window of NW flow Monday morning and early afternoon beneath a TROWAL. This deep wraparound moisture in the TROWAL and strong cold air advection across the lake combined with upslope flow could still result in a few extra inches in interior NE Ohio and NW PA in the snowbelts; it just probably will not last long given the ice cover and moisture stripping away quickly as the coastal low takes over.

Impacts with this system will be high areawide. Winds will not be very strong with it, but NE winds do increase to 15-25 knots Sunday followed by NW winds of 15-25 knots late Sunday night and Monday. This is enough given the dry snow to easily make it blow around, reducing visibility below a quarter mile at times and adding to the already snow covered roads. Wind chill values will also be a few degrees below zero tonight/Sunday morning and again Sunday night/Monday morning, and wind chills will only be in the single digits during the day Sunday. This will elevate cold exposure risks for motorists who become stranded in the snow. Travel is discouraged, but if you must travel, pack a winter weather kit containing a warm blanket, water, food, and portable chargers.

KEY MESSAGE 2... The deepening mid/upper longwave trough over the eastern CONUS in the wake of the storm will reinforce the pool of bitter cold arctic air. This combined with deep, fresh snow cover will allow air temperatures to fall well below zero Monday night into Tuesday morning, and increasing SW winds of 15-25 knots ahead of a Clipper system for Tuesday will lead to dangerous wind chills. Guidance has trended colder Monday night into Tuesday, and many areas will likely see air temperatures between -5 and -10 and wind chills of -15 to -20 late Monday night and Tuesday morning. Cold Weather headlines will be needed again as these temperatures and wind chills will create significant exposure risk. The coldest temperatures that we see in our region tend to occur when the wind is out of the SW like this because it prevents "warmer" Lake Erie air from coming onshore, so this will be monitored.

KEY MESSAGE 3... The arctic air will continue to hold across the region through at least the end of next week. The last time that our region experienced a stretch of this many consecutive days with temperatures averaging this cold (averaging 16 degrees or colder) was in early January 2018. Daily highs will struggle to climb out of the low to mid teens, and lows will fall to sub-zero each night. Lows Thursday night could be well below zero again. The consecutive days with these temperatures will elevate the risk of cold exposure and damage to infrastructure. In terms of snow, weak clipper systems will bring bouts of light snow to most of the region, with localized lake-effect snow continuing at times across NE Ohio and NW PA, although this will be limited by ice cover. These systems could amount to some 1 to 3 inch snowfalls, but confidence is low at this time. The most organized clippers look to be Tuesday night and again Wednesday night into Thursday. Timing and details will change as we get closer.

AVIATION /12Z Saturday THROUGH Wednesday/

VFR will continue today as upper- and mid-level clouds increase and thicken through the day. Light and variable winds become east-northeast around 6-9 knots by this evening. Snow spreads in from southwest to northeast late tonight, with snow onset between 05-11Z. Visibilities should quickly drop to between 3/4 SM and 2 SM, with periods of 1/2SM building in after 12Z Sunday. Visibilities could initially bounce around for a couple hours as it battles with initial dry air before sustaining 1 SM with continuous snow.

Outlook...Widespread snow will continue through Sunday evening before tapering off west to east late Sunday night through Monday. Snow will be moderate in intensity through the event but high snowfall totals are expected. Non-VFR with lake effect snow showers are possible in Northeast Ohio and Northwest Pennsylvania into Tuesday and again on Wednesday.

MARINE

Light and variable winds are expected today as high pressure builds overhead. East-northeast flow develops tonight, becoming 15-20 knots on Sunday. Winds become northwest on Monday and then southwest on Tuesday. Southwest winds should generally be around 20-30 knots, though there is a very low chance for gales (5-10%), especially in the far eastern basin. There is also a low chance for low water in the western basin as well.

Lake Erie is mostly ice-covered at this point and the ice will continue to expand and thicken through next week as several bouts of cold air impact the region. Stronger southwest winds on Tuesday may break up and shift the ice northeastward away from the southwestern shoreline of Lake Erie.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Cold Weather Advisory until 7 AM EST this morning for OHZ003- 006>014-017>023-027>033-036>038-047-089. Winter Storm Warning from 7 PM this evening to 7 AM EST Monday for OHZ003-006>008-017. Winter Storm Warning from 7 PM this evening to 10 AM EST Monday for OHZ009>014-018>023-027>033-036>038-047-089. PA...Cold Weather Advisory until 7 AM EST this morning for PAZ001>003. Winter Storm Warning from 7 PM this evening to 1 PM EST Monday for PAZ001>003. MARINE...None.