Ice and freezing rain in our area remain the most dangerous effect from the winter storm that is expected to impact over thirty states this weekend.
Expected snow totals continue to decrease, with 1″ to 2″ expected before moisture moves out of the area early Monday morning. Extreme cold is expected to move in early Monday.
Precipitation is expected to start as a wintry-mix of rain, sleet, and snow midday Saturday and continue until daybreak Sunday. Slightly warmer daytime temperatures on Sunday should change the precipitation over to all rain, before changing back to a wintry-mix in the evening and snow overnight.
Greene County could see icing and freezing rain, with heavier amounts in the northern part of the county. Areas in western North Carolina are in danger of an inch of ice.
After the moisture moves out, the area will be in a deep freeze for much of next week, with overnight lows dipping to zero on Tuesday. Any moisture or accumulation of snow or ice overnight Sunday is likely to last into the first part of the week and impact travel.
The weather pattern keeps a warmer pocket of air along the mountains, which may help limit the amount of snow or ice.
National Weather Service Forecast Discussion
A significant winter storm will impact the region, primarily Sunday PM into Sunday. Confidence is still limited on where the heaviest precipitation and duration of frozen precipitation will occur Saturday night into early Sunday morning. All types of precipitation (rain, freezing rain, sleet, and snow) are expected.
The heaviest snow accumulations (3 inches or more) are most likely along the Tennessee/Kentucky border and in southwest Virginia. The heaviest ice accumulations (over 0.25 inches) are most likely along the Cumberland Plateau, northeast Tennessee, the mountains, and just north of Interstate 40/81. Snow accumulations will be more limited further south with ice accumulations more uncertain along the foothills and southern Valley.
Extreme cold temperatures are expected Monday into Tuesday with highs well below freezing and overnight lows approaching or falling below 0. Lower wind chills are expected.
We are upgrading the Winter Storm Watch this morning. An Ice Storm Warning will now be in effect for SW NC and areas of southeast and central East Tennessee generally along and west of the Interstate 75 corridor and along and south of the Interstate 40 corridor. Significant ice accretion is expected for these areas with most locations receiving 0.25 to 0.5 inch of ice.
A Winter Storm Warning is in effect for northern portions of East Tennessee through SW VA where a mix of snow, sleet, and freezing rain is expected. The foothills of the mountains will see significant downslope winds and warming which will limit ice accretion in
these areas, and a Winter Weather Advisory has been issued for these areas. Ice accretion for the advisory area will be mostly 0.1 to 0.25 inch of ice with locally higher amounts further into the valley away from the mountain foothills.
In addition, we have added a High Wind Warning for the foothills of the mountains. A 50+ kt LLJ is forecast to be across the area on Saturday night and Sunday. With strong ducting and stable air, mountain wave winds are expected in the immediate vicinity of the mountains.
Windy conditions may exacerbate power outage and tree damage concerns across portions of the southern Cumberland Plateau, Lookout Mountain, Signal Mountain, Mowbray Mountain, and any higher ridgetops within the Ice Storm Warning on Saturday night as wind gusts across ridgetops increase to 30 to 40 mph with one-half inch of ice coating surfaces.
Currently, broad troughing is in place across the eastern U.S. with an impressive 1,050mb Arctic High moving down from Canada into the Northern Plains. A closed low is also noted off the Baja California Coast. Dry and cool conditions are expected to continue today with this initial setup. However, the pattern will quickly change as the closed low moves onshore in the southwest with the jet strengthening to its south.
The jet to our north will strengthen as well, increasing southerly 850mb flow, upper divergence, and isentropic lift. An eventual surface low will develop in the northern Gulf and track up the East Coast towards Sunday and Monday.
Saturday morning, northeasterly flow will remain in place at the surface as the Arctic High shifts eastward with 850mb temperatures beginning at or below freezing across the whole region. Based on the first run of several high-res model guidance, more significant dry air is being noted across the region Saturday morning into the early afternoon. This brings attention to lessened precipitation chances during the day, especially during the morning hours.
Throughout the day, southerly 850mb winds will gradually increase to 30 and 40 kts and beyond, leading to a northward shift in the warm nose. The focus for initial precipitation is generally along and north of I-40 by early afternoon, which would fall in the form of primarily snow with potentially some sleet, depending on the northward extent of the warm nose. It is not until Saturday evening into Saturday night when precipitation spreads throughout the region. The strong southerly 850mb flow will pull the warm nose entirely north of the region, leading to melting of snow before it reaches the ground.
The question continues to be how long places, especially in the Valley and foothills, stay below freezing. Based on the latest data, places in the southern Valley and the foothills (Monroe to County) will see the shortest window of freezing rain. For southern areas, this will be due to further proximity from northern cold air, and the foothills will be due to strong downsloping. Interstate 40 and 81 certainly delineate lesser ice accumulations to its south vs more significant accumulations (over 0.25 inches) to the north. These significant accumulations also look likely along the southern Plateau because of earlier onset and better access to colder air to the west. Snow and sleet accumulations have also trended slightly upward for places north of Interstates 40 and 81 because of this
initially drier air and slightly slower warm nose progression.
By the day on Sunday, 850mb flow will become more westerly but increase to 60 kts or greater, leading to even stronger winds in the mountains and broader WAA, turning precipitation back to primarily rain. In addition to WAA, this will also lead to better moisture transport and even heavier rainfall. By Sunday night, a front ahead of another Arctic High will move through the region, leading to significant CAA and a transition of lingering precipitation to all snow. Depending on how long moisture remains, additional light accumulations are likely, especially in the northern half of the region.
Very cold temperatures dropping well into the teens and even single digits can be expected with the lingering MSLP gradient producing winds and even lower wind chills. Moisture may linger enough with northwesterly flow to keep chances for snow showers in the mountains on Monday. Otherwise, the bigger story will be very cold temperatures area-wide on Monday, likely struggling to get out of the mid 20s for many. Lower wind chills are also possible. By Monday night into Tuesday morning, the Arctic High will become set up to our south with subsidence leading to extremely cold low temperatures. For any places that have snowfall, values below 0 are likely. Afterwards, general troughing and northwesterly flow remain in place aloft with weak WAA helping temperatures rise at least above freezing for most.
