Why is it Snowing in April?

We work in an industry all about controlling our indoor climates, but we’ve never really talked about our actual, natural climate. Why is it snowing in APRIL. We’re a few days into April, many days into Spring, and there’s snow in the ground. A few days ago it was sixty degrees outside and I was tempted to cook up some burgers on the grill and getting ready to dust off the lawn mower. What is with this weather?


Global Weather

The first thing to understand about the weather is that it’s not a local thing. The air all over the world is constantly moving, constantly carrying moisture, changing pressure, and changing the air temperature. Our local climate is controlled by our local geography and exposure to heat from the sun AND by events occurring thousands of miles away. On the one hand, we have the sun warming the ground around us, but on the other hand, air can move at hundreds of miles per hour in the jet stream. We’re experiencing this battle between energy entering our environment and just as quickly being effected by air from cooler environments.

What do we expect for our local environment (Philadephia/the US Northeast)? Highs in the 50s and 60s, lows in the 40s. We expect a good bit of rain fall, per the old saying “April Showers bring May Flowers.” That is, it’s a wetter season for us as part of Spring. We’re exactly in line with that, almost.

There is a ton of moisture in the air, which helps to explain the snow. There is a lot of heat coming in too. We’re seeing lows barely low enough for snow to survive and the ambient air temperature is rapidly causing snow to melt as it falls going into the afternoon. This snow was carried here from somewhere else. We had a mass of cold land in our back yard to get heated up. So, where do we look to know where this is even coming from?


The Jet Stream


A significant portion of our weather is driven by the Jet Stream. In the upper atmosphere, air flows west to east at potentially hundreds of miles per hour. These air currents are much like ocean currents, they shift and move, flowing north and south in different ways. If we follow the stream and measurements of air pressures, we can get an idea of what’s coming.

For this past snow storm, we can generally work out that the warm Pacific Ocean, where temperatures were probably in the 50s last week, provided lots of warm, moist air. This moisture traveled into the polar jet stream across Canada, cooled down, and was pushed southwards across the northern US and into our little corner of supposed spring time weather.

The local climate a few thousand miles away, impacted our local weather.


Climate Change

This becomes a more complicated issue when we consider the concept of climate change and global warming. We see small numbers, like the planet is on average 1-2 degrees warmer today than it used to be. This number is a bit misleading. It’s an average. When we blend all the extreme hot and cold together, we get that 1-2 number. Some regions like the equator will experience far more intense heating than others. In order for the North Pole to be two degrees warmer than the past, that would require somewhere like the tropics to be perhaps ten or twenty degrees hotter due to its more direct sunlight exposure.

If our local weather is impacted by the rest of the world, then a small warming in the south pacific can be an enormous snow storm in the North US once all that extra moisture hitches a ride across on the jet stream. We don’t directly see climate change in our local weather, but the symptoms are there.

Long term, our HVAC Industry is going to be perhaps one of the most heavily effected by our changing climate. As the weather outside grows more extreme, we will need better, more reliable, and more efficient technologies to effectively regulate our internal environments.

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