According to meteorological observations gathered at the Adirondack Regional Airport from National Weather Service equipment, the average temperature for December was 20.9 degrees Fahrenheit — only 0.2 degrees above the location’s normal monthly average of 20.7 degrees.

“That’s about as close as it gets,” said Scott McKim, the science manager at the Atmospheric Sciences Research Center’s Whiteface Mountain Field Station.

McKim has been with the Atmospheric Sciences Research Center since 2015. He studied meteorology in college and hydrometeorology in graduate school. Originally from New Jersey, McKim lived and worked in Alaska for a period before moving to the Tri-Lakes.

Even as the planet is warming overall, McKim said the Northeast, and specifically the Tri-Lakes area, are not warming nearly as fast as other regions of the world, such as the poles and much of Europe. He said that while there has been a general gradual warming and increased precipitation trend taking place, it’s not those overall topline trends that have caught his eye.

Nearly a foot of snow is seen on an outdoor table in Tupper Lake on Dec. 8. Snowfalls were punctuated by frequent thaws throughout December throughout the Tri-Lakes area. (Enterprise photo — Chris Gaige)

Looking under the hood, McKim said what is striking locally is a movement, in both directions, away from the average temperature and precipitation. It is through these extreme periods balancing each other out — on paper — that monthly conditions appear close to average.

Therefore, even though a month may be close to its normal average for temperature or precipitation, understanding it as such does not capture the full picture. McKim sees swings like this becoming more common in the Adirondacks. December, McKim said, was a perfect example.

“It was an unusually wide range of extremes,” McKim said in reference to the Adirondack Regional Airport’s — located about 5.5 miles northwest of Saranac Lake — December data.

McKim pointed to one particular stretch from Dec. 23 to 29, where the temperature swung from a -22 F low to a 52 F high — a difference of 74 degrees.

McKim said that was a “huge” range for the same location over any one month, let alone less than a week between the two extremes.

Ice melts on Long Lake during a balmy Dec. 29 — which saw a recorded high of 52 degrees Fahrenheit at the Adirondack Regional Airport. December weather for the Tri-Lakes area was marked by frequent swings between cold freezes and mild thaws. (Enterprise photo — Chris Gaige)

It was a similar story with precipitation. The airport finished December with 2.27 inches of liquid precipitation — including rain, and the liquid equivalent of snow when melted, which the observation equipment is able to calculate – compared to a normal monthly sum of 2.20 inches.

While the overall figure is close to its normal, 0.94 inches of the December total — or 41.4% — fell on a single day: Dec. 10. The next highest day was Dec. 11, with 0.17 inches of precipitation measured — as a result of a continuation of the same storm into the next day that was responsible for all of the precipitation on Dec. 10.

Even though no other day in December came close to the 0.94-inch one-day precipitation, the month was consistently cloudy, which McKim said was typical.

“We’re in this time of year where you get all of this crud and precipitation off of the Great Lakes,” he said. “We kind of get these permaclouds over the area. We’re in this for days and days.”

Going back to Nov. 20, there has been at least a bit of rain or snow that has fallen on almost every day, according to McKim — 45 of 46 as of press time Sunday, with the streak expected to grow throughout the week.

Snow falls on downtown Saranac Lake Thursday, Dec. 12. (Enterprise photo — Chris Gaige)

“There’s only been one 24-hour period where we haven’t gotten at least a trace of precipitation, which just speaks to the constant cloudiness,” he said.

McKim noted that the data from the Adirondack Regional Airport may not be a perfect match to conditions across the region. For instance, lake effect snow, which was a common weather feature for the Tri-Lakes throughout December, tends to result in hyper-localized areas of heavy snow, leading to highly variable totals within the area.

McKim said even though the data may not have been exactly what fell in someone’s backyard, it’s close enough to paint an accurate picture of the conditions the region experienced throughout the month. More importantly, he said it was helpful to compare data from the Adirondack Regional Airport for this month to normal temperature and precipitation values gathered from the same location over decades.

“The real value is being able to compare this December at the airport to other Decembers at the airport because it’s the same location,” McKim said.

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The science behind the swings

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The large variations in day-to-day weather conditions primarily come down to the jet stream’s pattern. The jet stream is a rapidly moving zone of air that generally moves from west to east high in the atmosphere. In addition to serving as a path for storms to track along, it tends to separate cold air to its north and warm air to its south.

Throughout much of December, the jet stream was amplified, what McKim said meteorologists refer to as a “long-wave pattern.” Under that setup, the jet stream looks like a meandering river, snaking up to the north – creating what meteorologists refer to as a ridge — and down to the south — what meteorologists refer to as a trough. This stands in contrast to a zonal pattern, where the jetstream moves west to east in a more-or-less level flow.

“Anytime you get a trough in the winter over the East, that’s always the result of a ridge building over the West,” McKim said.

McKim said that ridges, with the jet stream lifting north over an area, bring warm weather, while troughs, with the jet stream to an area’s south, bring cold weather. An amplified jet stream is not in itself an abnormal pattern. Ridges and troughs are common jet stream features.

What is more unusual is how quickly the ridges and troughs move from west to east, leading to sudden changes between extremes throughout the month. McKim said there were about three or four cycles in December.

“For the most part, they were pretty transient,” he said. “What we saw was a trough come in for three, four, or five days (which delivered) below normal temperatures and snow, and then a ridge would build in for the next two, three or four days, coincident with a big warmup.”

McKim explained that in order to get consistent wintery conditions across the Tri-Lakes area, there need to be atmospheric ‘roadblocks’ in place, which help to hold a jet stream trough in place over eastern North America for a longer time.

“(A) trough allows cold air from the North Pole area to drain south,” he said, adding that the pattern appears to be moving away from the sudden jet stream shifts to more consistent winter weather for at least the next couple of weeks.

“We’ve been flirting with these classic setups for the last two months — November and December — but now we’re finally in a solid … pattern, which is a ridge over the West and a blocking high over Greenland,” McKim said. “(This) has this longwave trough parked over the East Coast.”

He said that this will lead to a cold next couple of weeks for a vast swath of the country, and will turn back the clock — for now — on Adirondack winters.

“Florida is seeing temperatures in the 30s,” McKim said. “The 10-day forecast doesn’t have us getting above 15 degrees here, which is kind of like winters of old. … Painting the picture of a classic winter, this setup is much more classic of the 1970s or 80s, before things kind of got squirrely.”

McKim said the one major difference in that classic winter characterization is that traditionally, by this point in the season, the Tri-Lakes would already have a deep snowpack on the ground; but, due to the rapid cycling between cold and warm throughout December, most of the snow that had fallen melted away with the thaw between Christmas and New Year’s Day.

With the jet stream trough now in place and the atmospheric blocking setting up, McKim said the Tri-Lakes will have a chance to start rebuilding that snowpack. He said that while January appears less variable than December, it’s tough to predict how long the jet stream blocking will remain in place, with mixed signals for later parts of this winter.

“Now we’re set up really nicely, but it’s still anyone’s guess for February and March.”