Weather Science

It’s spring!! But, not so you’d really notice it.. Jet stream blues.

Since April fools day is just around the corner, many Rochesterians might be thinking the local meteorologists are playing some joke by forecasting highs that will barely reach the 40 degree mark along with a high possibility of a mix of rain and snow for Monday, April 1st. Unfortunately, that seven-day forecast graphic couldn’t be more accurate.

Although spring technically began March 20th, there has been little to no evidence of “spring” along the eastern seaboard so far this year. Rochester has been averaging about 4°F below the March average of 43°F. This is a far cry from a year ago as the average temp over the course of the month soared to 57°F. Without a doubt it is human nature to want to blame something for this awful spring.

So what do I blame?  I blame the jet stream.

What is a jet stream?

A jet stream is a thin current of rapidly moving air, flowing west to east, that is usually several thousand miles long and located in the upper part of the Earth’s atmosphere (~6–7 miles above the Earth’s surface). There are two main jet streams in each hemisphere, a weaker one in the subtropics, often crossing the southern portion of the U.S. and a more active jet in the mid-latitudes near the Canada/U.S. border..

This jet in the mid-latitudes is very active because of the collision of arctic and tropical air masses. The rapid change of temperature between these air masses near the surface, also known as the temperature gradient, creates a stronger jet aloft. Temperature differences create pressure differences, which leads to wind. Consequently, the greater temperature differences at the surface, the stronger and more active the jet aloft.

Because a jet stream is contingent on temperature differences, jets are most active during the winter over the mid-latitudes. As the northern hemisphere mid-latitudes begin to warm up into the spring and summer the jet stream moves north.

Why so cold, Rochester?

But so far this year, the jet hasn’t budged one bit. Unpleasant cold air has continually made its way into the Northeast from Canada due to a persistent pattern of surface lows, keeping the jet located to our south. Since the bitter air from Canada has been constant, the jet has not yet been able to begin its seasonal shift northward.

There is always hope though as the ground continues to warm throughout the spring. Eventually, the jet will start to push its way northward. And once Rochester is on the south side of the jet, say hello to swim trunks and tank tops.