Good Life

Focus on research: Understanding the weather roller coaster

Ben Reppert
Ben Reppert Photo provided

Editor’s note: The Focus on Research column highlights different research projects and topics being explored at Penn State. Each column will feature the work of a different researcher from across all disciplines.

As a winter-lover, I consider myself lucky to be a meteorologist. I do not need to wait until the third week of December to kick off winter. Meteorological winter is a three-month period that begins on Dec. 1 and runs until the end of February. Once December begins, central Pennsylvanians are set to get strapped into the 90-day weather roller coaster that lies ahead. On a theme park roller coaster, after the thrilling ups and downs, eventually you need to end up back where you started. The winter weather roller coaster doesn’t always work that way. This winter is a very good example of us not making it back to the starting position we call “average.”

Every winter has variability with mild spells, cold blasts, snow and rain. But this winter, the big atmospheric bully on the playground has been El Niño, which is an anomalously warm phase of the tropical Pacific waters. The area of water that gets tracked to determine the phase of the El Niño Southern Oscillation is roughly 4 million square miles. This is significant enough to not only affect the tropical weather patterns, but also the hemispheric circulation patterns around the globe.

When El Niño is present, the warm Pacific waters create a larger than usual temperature gradient between the equator and the middle latitudes, where we live. This acts to intensify the sub-tropical jet stream and allows for mild Pacific air to flood the continental United States and southern Canada, a pattern that was obvious earlier this winter when 27 states in the lower 48 witnessed their warmest December on record by extraordinary margins. For how wildly warm the holiday season was, I for one did not mind meandering outside on Christmas Eve in shorts and a T-shirt.

It was clear by the start of 2016 that the atmosphere was going to need to work very hard to overcome the effects of the Pacific air domination. December was so mild that much of central Canada was still not snow-covered, let alone the typical areas in the United States. When searching for ways to get a mature cold air mass to affect Pennsylvania, I like looking north. Cold air kept itself concentrated around the pole, although even the pole cold was above average. The fast Pacific flow and lack of snow were not great signs for winter-lovers.

In January, Canada was finally able to build some snow cover. As my colleague Fred Gadomski, Penn State senior lecturer in meteorology, likes to say, the atmospheric slot machine started to spin — signaling a time where the pattern was trying to change but it was unclear when and just how much of a flip was coming. In reality, the pattern rearranged itself in a way to allow for doses of chill to dip into eastern North America — two rounds in January and the big arctic blast earlier in February. These bitter bouts were transient, lasting just a couple of days; nothing like the past two winters when the arctic chill lingered.

The brushes with below-normal temperatures were not long or intense enough to wipe away the warmth of December, however. Despite a more average January-February period, the overall winter temperature departure will be strongly positive.

I suppose that Punxsutawney Phil may have factored El Niño into his prediction for an early spring. I do not speak “Groundhogese,” so I cannot really be sure. However, El Niño is slowly weakening. By later this summer, the tropical Pacific looks to return to a normal water temperature regime, which is sometimes referred to as “La Nada.”

Historically speaking, the temperature pattern in the month of March following a strong El Niño is not an overwhelmingly warm look in Pennsylvania. I am hesitant to jump on board for early spring warmth, although one thing I do feel confident about is for any cold air to continue to be transient, as opposed to lingering. There is still hope for the central Pennsylvania snow-lovers who did not benefit from the big January blizzard. In State College, where records date back to 1893, the top three and number five of the top 10 snowstorms have occurred during the month of March. Winter’s swan song may not have been scheduled just yet.

The bottom line for central Pennsylvanians is to take a win when handed one. This winter has not been nearly as harsh as the past two, not as harsh as it typically should be, and frankly not very harsh at all. No two winters are created equal, so while next December you might still be able to grill outside on Christmas Eve, be prepared to replace the Bermuda shorts with a burly overcoat and a beanie hat.

Soon it will be spring — the grass will get green, the birds will chirp and the days will get longer. Enjoy it, because as all weather-wise folks in the Keystone State know, we are only about 280 days away from when another central Pennsylvania winter will be set to begin.

Ben Reppert is a meteorologist in Penn State’s Weather Communications Group, and co-host of the department’s weeknight weather show, “Weather World.”