The fluctuation in temperatures NJ has experienced in the past several days is because of the jet stream and how it affects day-to-day weather across the country.

What is the Jet Stream?

The jet stream is a ribbon of fast-moving air in the upper atmosphere around 200 to 300 millibars (mb). The jet stream has two flows or orientations to it: a zonal flow and a meridional flow.

A zonal flow to the jet stream has a west to east flow, and is associated with nice, calm weather.

A meridional flow to the jet stream has a north to south orientation, and has two parts to it: a trough and a ridge. The trough is associated with clouds, cold air, or sometimes precipitation; while a ridge is associated with calm, warm weather like the zonal flow of a jet stream.

There are also entrance and exit regions of a jet stream as well. The entrance region is basically the start of the jet streak, and exit region is the end of the jet streak. A jet streak is a localized region of fast moving air within the jet stream. The jet streak can be further broken up into right jet entrances and exits, and left jet entrances and exits. The right jet entrance and left jet exit is associated with clouds or precipitation. The left jet entrance and right jet exit is associated with calmer weather.

What Caused Last Week’s Frigid Temperatures?

The orientation of the jet stream caused the below-freezing temperatures the past several days and the light snow event we had on Monday. The frigid temperatures that we experienced last week were the coldest we have seen so far in this winter season.

We were under a trough of the meridional flow of the jet stream. What caused these below freezing temperatures was due to a cold front that passed through during that time.

A low pressure system that moved through the northeast and up towards eastern Canada, with its counter clockwise motion of the low pressure system, brought cold, dry Canadian air down to the northeast. Because of this the 0 degree isotherm, also known as the 540 line, was well below New Jersey. When this happened, the temperature at the 850 mb level the past couple days was well below freezing.

The wind also played a major role in making the temperatures feel so cold. When temperatures are so low, such as in the teens and single digits, it takes only light winds to make the wind chill to be in the negatives and low single digits.

 Unseasonably Warm Temperatures

As the trough moves away, the ridge moves in and we feel a sudden increase in the temperature.

Temperatures have been in the 50s and 60s the past couple days and will be today. Under the ridge, the region tends to be warmer and a lot more pleasant compared to being under a trough. The 0 degree isotherm at the 850mb level has moved north, out of our region. But will return in the by the end of the day as another cold front moves through our area.

The fluctuation of temperatures the past several days is due to the jet stream and how it affects day to day weather across the country.