When will we see the first campus snowfall?

Nowadays, when you walk outside for your 8:30 a.m. recitation, you’ll notice a definite chill in the air. And on some days, your breath may even be visible in the crisp morning sun.

Fall is finally in full swing after a warm start to the school year. With temperatures that hovered in the 70s for a while in September, the average high in October is in the mid-60s, and it’ll only continue to drop in the coming weeks.

As cooler air begins to usher its way into our area, the topic on people’s minds is snow.

Philadelphia typically does not see measurable snowfall until the third week of December. That is, the Philadelphia International Airport — where all official snowfall, rainfall and other weather measurements are taken — does not usually register more than 0.1 inches of snow until then.

Still, it’s not a rarity to see snowflakes in the air well before then. When will we first see snowflakes falling, but not necessarily stick to the ground? And when will the first measurable snowfall be on Locust?

There are two major pieces of information that help answer these questions — the first being anomalies. Like I talked about with Hurricane Joaquin, meteorologists often look back at previous dates in history to see how the weather pattern then correlates with the pattern now. The earliest fall snowfall ever recorded in Philadelphia was on Oct. 10, which was also the date of the biggest October snowfall. However, some areas around the city greatly surpassed that during the Halloween snowstorm in 2011.

Overall, accumulating snow is rare for the first full month of fall. Even if there is snow in October, there usually is not a lot. Of the few instances snow has fallen before November, only a trace was recorded. So, is it fair to say that we shouldn’t expect any snow before the month is out? Well, not quite!

The second piece of the puzzle involves looking at the “bigger picture” weather pattern. By now, many of you have heard of the phenomenon known as El Niño. Currently, it is sitting in an extremely strong state, meaning that a large chunk of water in the Pacific Ocean is extremely warm.

Why is a body of water thousands of miles away relevant to snowfall on campus? Well, a climate anomaly known as the Arctic Oscillation is used by meteorologists, especially in the winter, to determine how much cold air will move into the area from the Arctic circle. When it is negative, the colder it is in and around the Northeast United States and vice versa. However, a strong El Niño tends to push warm air and precipitation into the continental U.S. So, if you have a negative AO and a strong El Niño, it’s possible that the colder air could beat out the warm air and combine with the moisture from a strong El Niño to create snowstorms.

Right now, the Arctic Oscillation has been hovering around neutral, but it is forecast to dip down into negative territory in the coming days. Unfortunately, it is very difficult to forecast for the AO weeks in advance. As of now though, it looks as if the warm air from the El Niño will win out in the long-range because not all of the “ingredients” look like they will come together at the right time for snowfall. We may see cold shots every now and then, like this weekend, where temperatures dip to freezing at night and 50s for the daytime, but we need more precipitation in Philadelphia for any snow to fall.

So, when will the first measurable snowfall be on Locust? Probably not for a while — anytime between mid-December to early January.

When will we first see snowflakes falling? The first flakes could fall on campus before Thanksgiving break, but it’s more likely to occur during finals season.

But if you’re thinking that this winter is going to feature little to no snowfall because the chances of snowfall in the next few weeks are slim, you may want to rethink that. A recent blog by WSI’s Todd Crawford showed that a negative AO in the summer is usually followed by a negative AO in the winter. The AO was negative for almost all of July and parts of August. So, regardless of El Niño’s influence, the Arctic Oscillation could win out in the long run.

That is, you may need a heavier winter coat than you think.

Elyas Tecle is a College freshman and meteorologist reporting on weather for The Daily Pennsylvanian.

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