Posted on November 10, 2015 by Corey Davis
Our 2015-16 Winter Outlook series begins today and concludes on November 23rd. In these five posts, we will discuss predictions and patterns that may shape North Carolina's winter weather.
Folklore is a popular source for predictions about the weather, and North Carolina has a rich collection of winter weather folklore, ranging from insects to almanacs to the weather itself. Our first Winter Outlook post looks at a few bits of folklore to see what they say about the coming winter.
Winning worm Twinkle Toes and entrant Rebecca Perree from Palm Beach, Florida. (Photo by Jim Morton/Woolly Worm Festival)
The story of the woolly worm as a winter forecaster began in the 1950s, when a museum curator in New York related brown bands on the worms with milder winter conditions. The science says that brown bands appear as the worms grow, which is affected more by warmer weather in the previous winter or spring than in the coming one.
Still, the woolly worm and its purported weather forecasting abilities are embraced by the town of Banner Elk in the North Carolina mountains, which has held an annual Woolly Worm Festival each October since 1978. Worms from across the state race up a rope, with the winner becoming the Festival's official winter forecaster.
This year's winner was Twinkle Toes, a mostly brown worm that suggests a mild winter overall. Examining its multi-colored segments from head to tail, the bands indicate a cold and snowy start to December, followed by near-normal temperatures and little snow through mid-February. The final weeks of winter may return to a cool pattern with some snow, according to Twinkle Toes.
To make their popular winter predictions, two long-established almanacs use well-guarded formulas that account for both weather patterns and astronomical observations.
The Old Farmer's Almanac, first published in 1792, calls for a wet winter across the Southeast US, but not necessarily a snowy one:
Winter will be colder and rainier than normal, with below-normal snowfall. The coldest period will be in mid-January, with other cold spells in early to mid- and late December, most of January, and early February. The snowiest periods will be in mid- to late December and early February, with icy periods in early and late January.
The Farmers' Almanac, which dates back to 1818, calls for "Wet & Very Chilly" weather and notes that "an active storm track will bring above-normal precipitation to the Southeast States".
A pair of famous sayings suggest that the weather in August can predict conditions in the coming winter. The origins of these sayings are unknown, but they may come from the time when explorers used the late-summer weather to assess whether to set off on wintertime journeys. Or like the woolly worm, someone may have connected conditions in a few years and applied it to all years.
In any case, we put these sayings to the test using historical weather data from several stations across North Carolina.
For every fog in August, there will be a snowfall in winter.
Fog observations since 1997 from five manned airport-based weather stations show an average of 3.16 foggy days each August, with Asheville having the most (8.06 days) and Charlotte having the fewest (1.22 days).
|August foggy days and winter snow events since 1997|
By comparison, those sites average 5.19 snowfalls -- defined as single or consecutive days with snow observed -- per winter, which is 64% more than the number of foggy days. Only in Wilmington are the average number of August fogs (1.78) and winter snowfalls (1.39) within 30% of each other.
We can also test how well-correlated the values are -- in other words, whether foggy Augusts tend to precede winters with more snow events. Comparing the two historical datasets gives us a statistical measure called an R² value, which tells how similar the datasets are. An R² value of 1 indicates a perfect fit between the two datasets, while a value of 0 indicates no similarity.
In this case, the average goodness-of-fit R² value is just 0.061, indicating essentially no relationship between August fogs and winter snow events.
If the first week in August is unusually warm, the coming winter will be snowy and long.
Using historical records from these same five locations since 1949, we compared average temperatures from August 1st through 7th with total snow amounts and snow days during the following winter.
|August 2015 weather conditions|
Temp. (vs. Normal)
The results were equally unimpressive, with an average R² value of 0.001 when comparing first-week-of-August temperatures with wintertime snow amounts and 0.004 when comparing the temperatures with the number of snow days.
If you're curious, this year's August conditions paint a mixed picture for the winter, according to the folklore. All five locations had three or fewer foggy days during August, which would mean limited snow events this winter. However, temperatures during the first week of August were about 2 degrees above normal, which forebodes a snowy winter per the folklore.
Although neither of these August sayings is confirmed by the data, it's not a surprise, climatologically speaking. Our summer weather conditions generally don't tell us much about how the coming winter might play out.
For a more scientific look at the winter forecast, stay tuned to the blog as we cover Pacific and polar patterns, plus our official winter outlook, in the coming weeks.