Blazing foliage this October contrasts with blazing warmth of past falls

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The rapid advance of changing foliage is a colorful marker for what has, thus far, been one of the coolest Octobers that Southwest and Southside Virginia have experienced in several years.

The intensity and relative earliness of fall colors, spilling out of the mountains where they are near peak in some locations and into the Piedmont, where color is spottier, have been noted by many media and social media sources in recent days.

Fall foliage is not entirely dependent on temperature, but the cool mornings followed by sunny, warm afternoons in much of September and the first half of October are a pretty good recipe for rapidly changing and intensely colored fall foliage.

Last year, by contrast, much of our region along and east of the Blue Ridge didn’t really hit the peak of fall colors until early November, which gets us to the major point of today’s column.

The first half of this October has indeed been cooler than normal, averaging 1 to 4 degrees below the 1991-2020 normal across our region over the first 16 days of the month, with the ongoing arrival of the first real punch of Arctic air likely to drive that average even a little lower entering the second half of October.

But some of our perception of this month’s coolness is also that so many recent early Octobers have been really warm.

The first 16 days of October in 2017, 2018, 2019 and 2021 rank among the warmest such periods on record going back more than a century for each of the National Weather Service’s four major climate stations under the Cardinal News umbrella.

The first half of October (plus a half day, since it doesn’t break even with a 31-day month) for those four years ranked, in varying orders, second, fourth, fifth and sixth warmest going back to 1893 at Blacksburg; two of them tied for second, ninth and 12^th warmest going back to 1917 at Danville;  second, fourth, 10^th and 13^th warmest going back to 1893 at Lynchburg; and second, third, fifth and seventh warmest going back to 1912 at Roanoke.

Seven years at Blacksburg and 12 years at Danville with more than one day of missing data between Oct. 1 and 16 were not included in the averages, none later than 1994. There was only one Oct. 1-16 period with more than one day of missing data at Roanoke (1916) and Lynchburg (1895).

Very generally, warmer early fall weather is expected with rises in global average temperature — not every year, owing to natural variability, but more often.

More regionally specific, there are two main situations in which early fall temperatures rise above the pack: large-scale summer weather patterns lingering or recurring, and early fall patterns dominated by tropical systems.

Early October 2019 clearly fits in the first category. After a September with highs in the lower to mid 90s into the last week, the first three days of October soared into the mid and upper 90s, nearly identical to the brutally hot pattern experienced in early October of 1941.

For Roanoke, Lynchburg and Danville, 1941 is the runaway winner for early October heat, and it really is for Blacksburg too, but that year had two missing days in Oct. 1-16 data and was disqualified.

The pattern of strong high pressure positioned south of our region, clockwise rotation pumping southwest winds further heated by downslope flow over the Appalachians, was present in early October both in 1941 and 2019 – it just lasted a little longer in 1941.

Temperatures hit the upper 90s across Southside and lower elevations of Southwest Virginia both times.

Warm early Octobers in 2017 and 2018 were dominated by tropical activity – remnants of hurricanes Nate and Michael, particularly.

Air masses of tropical origin have high dew points, which hold nighttime lows considerably warmer even if daytime highs aren’t really hot, raising average temperatures.

Early October 2021 didn’t neatly fit in either category, but had elements of both, with sticky weather lingering from earlier tropical activity and lots of warm nights.

So that gets us back to why this October has not followed suit with the warmth of four of five previous years.

First, no lingering summer patterns affecting us. The heat dome high translated west with time, not east, That rotated in cool, dry air from Canada, allowing some cooler mornings even on sunny days with fairly warm highs.

Secondly, the tropical season in the Atlantic started late and has mostly been focused to the east and south of the continental U.S. Even the tropical system that did directly affect us, Hurricane Ian as September flipped to October, got absorbed by a much cooler regime pressing from the north.

Now, this week, we have truly Arctic air pressing in to further the coolness of October as we enter the second half. There were reports of snow flurries at several locations north and west of Interstate 81 on Tuesday – this writer saw some himself at Blacksburg.

But the blustery gusts might also start to blow away some of the colorful leaves.

Weather Stats of the Week

Let’s spell out the early October coolness more specifically.

Danville averaged 57.9 degrees over the first 16 days of October, the coolest in 26 years, since a 57.2-degree average for Oct. 1-16, 1996. That is the 11^th coolest among 95 years with no more than one day of missing data in the Oct. 1-16 period.

Blacksburg’s average temperature of 51.9 degrees for Oct. 1-16 is also the coolest such period in 26 years, since that same period averaged 51.1 in 1996. That is the 20^th coolest among 123 years with no more than one day of missing data in the Oct. 1-16 period.

Roanoke averaged 58.4 degrees over the first 16 days of October, the coolest in a decade, since 57.9 for Oct. 1-16, 2012. This ranks 33^rd coolest among 110 years with no more than one day of missing data in Oct. 1-16 period.

Lynchburg averaged 58.8 degrees for Oct. 1-16 of this year, the coolest such period in seven years, since 58.5 in 2015. This ranks 47^th coolest among 129 years with no more than one day of missing data in the Oct. 1-16 period.

An interesting facet to Wednesday morning low temperatures around the region: Danville dropped to 28 degrees, tying a 1948 record low for Oct. 19, while Blacksburg only dropped to 35 and Roanoke to just 40. Lynchburg did barely make it to freezing at 32. Usually, Danville is the warmest of the four major climate stations in Cardinal News territory. But clouds and downslope winds held temperatures up nearer the lee side of the Appalachians while skies cleared and winds calmed farther east in Southside, allowing greater radiational cooling to occur.

Weather ahead

The winterlike chill will be short-lived, as the continental weather pattern appears ready to do a flip-flop with cold air settling into the West and warm temperatures in the East next week. We’ll be back to 60s and 70s for highs by the weekend. There are some signals that cold air may return near Halloween but this is too far out for much confidence at this point.

Weather photos

You may notice several photos here by people other than the author of the column. Feel free at any time to email weather photos to weather@cardinalnews.org or tweet them to @CardinalNewsVa or @KevinMyattWx for possible consideration for use each week with this Wednesday evening weather column and/or selection as the Weather Photo of the Week in the weekly Cardinal Weather newsletter. Please include location and date of photo and generally what is being pictured.

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.