It’s been “feast or famine” in the snow department around here for quite a while. These are the official snow totals for Philadelphia during the past five winters:
The long-term average snowfall is about 22 inches. Yet no recent year has even been close to average. Going back to the 1880s, when official records began, there are NO examples of any stretch of “all-or-nothing” snow seasons.
So, what would I expect this year? It looks like another extreme winter is in store-on the high side for snow again.
The 2009-10 and 2013-14 winters were the two snowiest on record here. While I won’t go that far out on a limb and predict anything close to those numbers, I do expect another winter of 40+ inches. That’s WAY above average. Again. And this winter could end up even colder than last winter, which wasn’t as cold as you might think. The Midwest and Upper Plains got the brunt of the cold. We got the snow-over and over again.
We have to look all over the world for connections to our winter weather. They’re called “teleconnections”, and there a lot more than there used to be. Back when I started winter forecasting on NBC10 in 1997, there was only one I used: the developing strong El Nino. So, let’s start with that.
In 1997, a huge El Nino was setting up. It’s an area of warmer than normal water in the tropical Pacific, and it can cover an area bigger than the entire U.S. Here’s the 1997 map:
The El Nino is the enormous red area from the coast of South America practically all the way to Australia. It was the strongest one ever recorded, and it would lead to a warm winter with very little snow here.
This year, the El Nino appears to be weak. So, rather than helping to flood the U.S. with warm air, weak El Niño’s often lead to more coastal storms and colder air around here.
It’s warm in the Tropical Pacific, but not that warm. A more impressive area of warmth is right off the U.S. and Canadian West Coasts. That represents another factor in our coming winter.
That warm water off the West Coast is related to a couple of things. First, months and months of drought helps High pressure anchor itself in the Western U.S. and just offshore. That means lots of sunshine. And that helps warm up the ocean.
The warm water is also related to longer-term ocean patterns, known as the PDO (Pacific Decadal Oscillation) and EPO (East Pacific Oscillation). Both were strongly tied to our persistent cold, snowy winter a year ago. Those factors once again favor cold and snow for us.
Here’s a map from NOAA showing a "classic" +PDO pattern. That sure looks a lot like the global map shown above:
A lot has been said about that this fall. I’ve been following this teleconnection for a decade or more, watching Dr. Judah Cohen’s research connecting October snow in Siberia and all of Eurasia as great predictors of snowy winters for us. The more snow there, the more snow here. Below is a map of unusually large snow extent as of October 31.
Of course, we scientists have to use numbers and make calculations-we can’t just look at a map and make specific predictions. So, welcome the SAI (Snow Advance Index) and the SCE (Snow Cover Extent). One covers how much the snow advances southward during October, and the other the total area covered by snow by the end of the month. The snow area is the 2nd biggest on record-2nd only to 1976 (one of the most brutal winters in the U.S.). It could hardly be more favorable for cold and snow for our area!
We’ve also heard a lot about the AO (Arctic Oscillation) and NAO (North Atlantic Oscillation) in recent snowy years. When HIGH pressure gets stuck in these far north places, traffic jams are created in the atmosphere. Our cold and snow becomes related to where the HIGH is located. The traffic jam, or blocking pattern, can lead to a persistent cold flow from the Arctic to the U.S., or storm after storm developing off the East Coast (Nor’easters).
The Arctic Oscillation was a big factor in our record snow winter of 2009-10. The AO was strongly negative practically all winter, locking in the cold air, and leading to practically all storms bringing snow rather than rain. But it wasn’t a factor last winter: the EPO/PDO dominated everything. So, what happens when the EPO, PDO, and AO all point in the same direction? COLD…..COLD …. COLD!
The NAO tends to be more variable than the other indices, but when it’s negative, Nor’easters become more likely. If we’re swamped with warm air from a strong El Nino, it just means a lot of big, rainstorms. But a weak El Nino combined with a prevailing negative NAO is heaven to snow lovers. There are strong indications that the NAO will be predominantly negative this winter.
The final teleconnection I’ll mention is way up in the stratosphere, more than six miles up. Winds there switch from East to West for months or years at a time, and is called the QBO (Quasi-Biennial Oscillation). When it’s Easterly, it’s a negative QBO, as is the case now. This tends to favor more blocking patterns near the ground. And, as we’ve seen, blocking patterns can lead to extreme weather.
There just don’t seem to be ANY indications of a mild winter with little snow. Things can and do change in the atmosphere and oceans, so this isn’t set in stone, but it’s about the odds. And, as of now, the odds favor a snowy and cold winter.
*COLDER THAN LAST WINTER
*COLDEST SINCE 2002-03
*>40” SNOW 4th of last 6 YEARS
*FEWER DAYS WITH SNOW THAN LAST WINTER
*AT LEAST 2 STORMS OF 12”+
*POSSIBLY MORE SNOW SOUTH OF PHILA.
Glenn “Hurricane” Schwartz