Highland County got a dusting of snow early last week from upslope northwest flow over the Appalachians. Much of the moisture for upslope snow bands common in our mountains with northwest winds in winter originates from the Great Lakes – but the amounts are much, much less than what piles up near the downwind lakeshore. Courtesy Rain Hupman.
Highland County got a dusting of snow early last week from upslope northwest flow over the Appalachians. Much of the moisture for upslope snow bands common in our mountains with northwest winds in winter originates from the Great Lakes -- but the amounts are much, much less than what piles up near the downwind lakeshore. Courtesy Rain Hupman.

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One thing we can give thanks for on this holiday – even 99% of die-hard snow fans – is that Virginia doesn’t get 60 to 80 inches of snow in a single pop the way southern suburbs of Buffalo, New York, did Thursday to Sunday.

Last winter, 6 to 12 inches of snow was enough to stall traffic overnight on Interstate 95. Snow that could bury a college basketball center is outside our realm of experience – thankfully.

Aside from a few higher elevation locations in Shenandoah National Park or the western fringe of the state, nobody in Virginia has ever seen 80 inches of snow in an entire late fall to early spring period, let alone in a single winter storm, as was reported this past weekend in Orchard Park just south of Buffalo. Most places in Virginia typically take several years to accumulate that much snow.

But Virginia does in fact get lake-effect snow, pretty regularly.

Quick reminder: The first Cardinal Weather snowfall prediction contest will continue taking entries through midnight on Friday. See how to enter at the end of this column.

And it is from moisture supplied by the same Great Lakes famous for the house-burying dumps on some of its shorelines.

The lake-effect snow Virginia experiences primarily affects the mountainous part of the state north and west of Interstate 81 and is more commonly referred to as “upslope” snow showers. But it is very much an extension of the same mechanism that spawns the plumes of snow nearer the lakes.

Lake-effect snow occurs when cold wind blows over relatively warm water. The moisture from the warmer lakes rises and condenses into clouds and snowflakes in the colder air above. Stretched into a narrow plume by the prevailing wind flow, the moisture is further lifted when it reaches shore and the slightly higher terrain there above lake level (or up to 2,000 feet higher in the case of the Tug Hill Plateau in northwest New York, where this weekend’s herculean amounts are even more common than the greater Buffalo area).

The National Weather Service office at Buffalo, New York, “only” got 3 feet of snow from a prolonged weekend lake-effect snow event, less than half as much as some suburbs to the south of Buffalo got. This would still be a rare and paralyzing amount for our region. Courtesy National Weather Service.

But that same band of moisture can continue much farther. Northwest winds behind Arctic cold fronts that have blown over Lake Superior and Lake Michigan cross the relatively flat terrain of Ohio and Indiana before running into the Appalachians.

So the moisture is lifted again as winds climb the mountain range incline, and snow bands often regenerate or intensify crossing the Appalachians. This is that familiar upslope snow that seems to happen in the mountainous parts of our region almost every time the wind turns to the northwest in the colder months.

This chart shows how winds blowing up a mountain slope cause precipitation to occur, often snow when it is cold enough. (Mountains depicted are more like the Rockies than the Appalachians, but effect is similar.) Courtesy National Weather Service.

By this time, it isn’t the firehose of moisture it was coming fresh off the lakes, not as thick or focused. So that’s why the Appalachians don’t get clocked with 6 feet of snow when the lakes moisture arrives. A prolonged upslope flow can sometimes bring 1-2 feet in the highest elevations near the western side of the Appalachians. Cheat Mountain, the site of Snowshoe Mountain ski resort, often gets bonus snow from Great Lakes moisture blowing over it.

Reaching Virginia, the lake-effect/upslope snow is often in parallel narrow bands that can be quite heavy near the core of each, gradually diminishing as they move southeast and the average elevation diminishes crossing a series of ridges. Still, a few to several inches can sometimes fall on and near the first ridge or two they pass over in far western and southwestern Virginia.

The snow dwindles out quickly passing the Blue Ridge into the Piedmont, as downslope flow has the opposite drying and warming effect compared to upslope flow, with maybe only a few flurries reaching Southside or Central Virginia in a particularly vigorous episode.

Upslope snow, caused by moisture lifted by northwest winds blowing over the mountains, takes on parallel bands on radar moving over western Virginia last January. Courtesy RadarScope.

With upper-level lift from a disturbance aloft or some added instability from sunshine into colder air aloft, the upslope bands sometimes have a little extra life, spreading accumulating snow as far east as near Interstate 81 or the Blue Ridge. Maybe once every winter or two, I see a sudden ground-whitening, visibility-choking snow squall at my location south of Roanoke at a somewhat higher elevation than the urbanized valley.

Once the Great Lakes cool considerably or mostly ice over later in the season, the moisture supply for lake-effect and downwind upslope snow is reduced substantially.

Recent observations have found the average water temperature of the Great Lakes to be increasing and that it is icing later, not as widespread and less reliably on average (varies season to season) than it once did. This creates the conundrum that a warming climate could lead to greater lake-effect snow on its shores and perhaps for the mountain slopes downwind as well.

Lake-effect snow has a cousin that sometimes affects the Hampton Roads areas, the Eastern Shore or the western fringe of Chesapeake Bay.

The band of clouds on the horizon was kicking some snow showers over Chesapeake Bay and into the Hampton Roads area, as seen over the York River near Yorktown, Virginia, in November 2019. Photo by Kevin Myatt.

When the Arctic wind turns to a north to north-northeast trajectory, it can sweep down the length of Chesapeake Bay and develop a “bay-effect” plume of snow that blows into parts of Hampton Roads. Locations under the band might get a few inches while the sun is shining a few miles away outside of it. This doesn’t happen often and is more novelty than nemesis.

In theory, if a cold wind gets turned in the right direction to sweep across relatively warm water for several miles, even a large reservoir like Smith Mountain Lake or Kerr Lake could produce a narrow band of snow downwind from it.

How lake-effect snow forms. Courtesy National Weather Service.

The narrow Finger Lakes of New York sometimes have their own lake-effect bands when the cold wind blows down the length of them.

Lake Lanier near Atlanta even produced a plume of lake-effect snow in 2020.

I am aware from my early life in Arkansas of one situation where some locations on the west side of the Mississippi River got quick bursts of heavy snow from cold wind orienting in a fetch over the river for several miles.

And then there is the odd case of “power plant effect snow” – that steam from a large power plant rising into colder air aloft triggers snow downwind from it. It happens more than you might think, but usually not as dramatically as in this YouTube video from Oklahoma posted by famed storm chaser Reed Timmer.

Back to regular weather. The frequency of upslope snow from Great Lakes moisture forced over the mountains is such that some places near our western border and west of Interstate 77 often get an inch or two of snow with very little mention in the forecast.

This column will certainly not attempt to note every instance in which there may be upslope snow showers. Just generally expect some snow in the western fringe behind every cold front now to April. Some locations, as the submitted photos from Highland County show, have already gotten dusted by upslope snow this month.

In Southwest and Southside Virginia as a whole, it’s when the Gulf of Mexico and the Atlantic Ocean get involved, while keeping the cold air in place, that we get our larger and/or more widespread snowfalls.

That’s what we’ll be on the lookout for in the weeks ahead.

Low-level clouds blowing over the mountains from West Virginia contain Great Lakes moisture that has been lifted by northwest flow over the mountains, resulting in bands of light snow early last week in Highland County near the West Virginia line. Courtesy Rain Hupman.

Stats of the week

The coldest temperature I have found reported in this recent spate of Arctic air in Southwest and Southside Virginia was 12 degrees – Sunday morning at an automated sensor operated by Virginia Tech at Grayson Highlands State Park and then Monday and Tuesday mornings at the volunteer co-op station in the icebox of Southwest Virginia, Burke’s Garden in Tazewell County.

Our entire region flipped a switch from unseasonably warm to unseasonably cold air between Nov. 12 and Nov. 13. At Danville, it was the warmest Nov. 1-12 period in more than 100 years of temperature records, averaging 63 degrees, more than 2 degrees above the 60.8 for the Nov. 1-12 period in 1977. But then, the Nov. 13-21 period was the second coldest such period on record at Danville, averaging 38.2 degrees, beaten only by the 36.8-degree average for the same Nov. 13-21 period eight years ago in 2014.

Looking ahead

Milder weather, but not runaway warmth, is upon us, with lots of days in the 50s and 60s for several days ahead and lows mostly above freezing. Low-pressure tracking west of our region will spread periods of showers over this Thanksgiving weekend, particularly Black Friday and Sunday. That will clear out early next week but it will not get dramatically colder even behind a cold front. More winterlike cold may ooze or surge back into our region in early December.

Snowfall contest

So as you gobble turkey and other trimmings at the Thanksgiving table, why not poll the room about snowfall expectations in our region this winter?

Friday at midnight is the deadline for entering the first Cardinal Weather snowfall contest. If you’ve been meaning to enter it, but haven’t yet, do it now (if it’s not already Saturday). We’re really close to reaching the goal of having more than 100 entries.

To enter, just send me an email at weather@cardinalnews.org, put “Snowfall contest entry” as a subject line, give me your name and where you live (general area, like a town or part of a county, not specific address), then guess the date of the first 1-inch snowfall and total snowfall rounded to the nearest inch between Dec. 1 and March 31 for ANY TWO of the following six major climate stations in and near Southwest and Southside Virginia: Bluefield, W.Va.; Blacksburg; Danville; Lynchburg; Roanoke; and Tri-Cities Airport, Tennessee (just across the line from Bristol).

It is OK to send one email with your prediction and that of your spouse, each of your children, your parents and grandparents, uncles, aunts, cousins, and whoever else is in your house on Thanksgiving Day.  I’ve promised a $25 gift card to the winner – but mostly just the glory of being recognized next spring, about the time we’re ready to forget about winter, as the region’s superior winter prognosticator. It costs you nothing to enter.

For a fuller description of the contest, scroll to the end of my last Cardinal Weather column linked here. Read the whole column for a wider discussion of the ins and outs and regional snowfall.

I said last week I’d put skin in the game with my own entries, for all six locations. Generally, my expectation hinges on long-term model indications of colder patterns intermittently until Christmas, a tilt to milder weather more like a typical La Niña pattern in January, with a late resurgence of colder weather in February and early March. So my snowfall guesses are very slightly above normal. First snowfall date is a total guess, but leaning to December dates.

So here they are.

Bluefield: Dec. 5, 35 inches; Blacksburg, Dec. 10, 27 inches; Danville, Dec. 20, 10 inches; Lynchburg, Dec. 20, 17 inches; Roanoke, Dec. 20, 19 inches; Tri-Cities Airport, Tennessee, Dec. 10, 13 inches.

Please don’t copy these – especially if you want to have a serious chance at winning.

Journalist Kevin Myatt has been writing about weather for 19 years. His weekly column is sponsored by Oakey’s, a family-run, locally-owned funeral home with locations throughout the Roanoke Valley.

Kevin Myatt

Kevin Myatt wrote the Weather Journal in The Roanoke Times for 19 years. He has led students on storm chases and written for “Capital Weather Gang.” Twitter: @KevinMyattWx. Email: weather@cardinalnews.org.