Looks like fall, feels like summer
Out for a family stroll Tuesday, Beth Ackerman pushes 1-year-old Ruby while Rex Whiting, 4, walks with them among the tree-lined streets near Church and Center streets in Bethlehem. The warm weather expected all week makes for nice outings, but don’t read anything into it in terms of what the winter has in store,
Woolly bear caterpillars — also called woolly worms or banded worms — meandered around Blue Mountain in Palmerton on Sunday, attracting the same level of interest from hikers as the brilliant fall foliage.
The caterpillars, which will later turn into tiger moths, are experiencing the stage of their life cycle where they’re popular as tiny weather prognosticators. A bigger brown band is said to signal a mild winter, while black woolies are a harbinger of a harsh winter ahead.
Folklore aside, the weather the region is experiencing now often is believed to give us a clue about the upcoming winter season. That’s because people embrace autumn as a time of transition, looking for the hidden meaning behind the first frost, the appearance of the woolly worm, or squirrels on their frenzied quest for a buildup of overwintering fat.
The truth is, autumn is no crystal ball to winter. Summerlike warmth will persist in parts of the country in October — including in the Lehigh Valley this week — while winter cold builds and frozen precipitation falls in other areas. A blanket of snow covered northern New England over the weekend, while the Mid-Atlantic region enjoyed seasonable temperatures and plentiful sunshine.
The current weather pattern is generally not predictive of anything over the longer term, according to meteorologist John Homenuk of Empire Weather, which provides local forecasts for The Morning Call.
Meteorologists across the country say that cold snaps and early snowstorms can occur just as easily before a mild winter as a harsh one. A more recent example is the pre-Thanksgiving storm of 2018 that dumped 8.1 inches of snow and paralyzed the entire region. We had just 16 inches of snow combined in the three months that followed.
What meteorologists do have to work with are forecast models and analog research, such as past years that line up with current outlooks. They study sea surface temperature anomalies and predictors of climate patterns such as El Nino or La Nina. Uniform models, which meteorologists are seeing this year, are a good indicator of what the upcoming winter could be like.
The seasonal outlook published by the National Oceanic and Atmospheric Administration last week included maps with areas colored to indicate the odds that temperatures or precipitation will run above or below a normal winter. They showed milder-than-average conditions just about everywhere but the northwestern tier of the country.
Meteorologists will caution that uncertainties in the data will only permit an educated guess on the future, and that winter outlooks don’t project seasonal snowfall accumulations or individual snowstorms. Detractors say the odds of them being accurate are slim, but the confidence on temperature trends is high. NOAA’s map shows values above 50% to 60%, meaning that forecasters are at least that confident the outlook may prove correct.
The confidence levels for precipitation are much lower, with a large swath of the country (including the Lehigh Valley) having an equal chance of drier than normal or wetter than normal conditions.
Empire Weather recently took its first whack at a winter forecast as well, focusing heavily on what La Nina would mean for the country.
“Typically, La Nina favors the coldest risks in the prairies, the upper Midwest, and the northern Plains. It also features a fairly strong northern Pacific jet stream. That’s why we see the Pacific Northwest typically on the wetter side, and it’s also why we see parts of the Great Lakes and the Agriculture Belt wetter as well,” said meteorologist Ed Vallee in Empire Weather’s outlook.
To the south, La Nina brings drier and warmer conditions. The Mid-Atlantic is caught between the wet and dry and somewhat unaligned to trends.
“December typically favors some [cold air] intrusions into the Northeast,” Vallee said. But there are no huge signals for January and February, meaning temperatures could be fairly warm.
“It’s an interesting evolution. We favor December to have the coldest risks. In January maybe it backs off a little bit and February ... it could get warmer in the east again.”
A cold December? A white Christmas?
The expectation of La Nina conditions is one of the drivers of winter outlooks from both AccuWeather and The Weather Channel.
Both forecasts call for an early season chill and suggest we could be in for a cold December. AccuWeather believes there will be “opportunities for snow in some of the bigger cities across the region heading into the holiday season.”
The Weather Channel says, “The typical La Nina response is for warm November, cold December, and warm January/ February; however, January and February can have significant volatility depending on if high-latitude blocking occurs.”
High-latitude blocking changes the jet stream pattern and could allow Arctic air to descend into the region (also known as the polar vortex).