– NWS Jet Stream Illustration

The Polar Jet Stream

All weather phenomena here on Earth occur within a layer of our atmosphere, the Troposphere, due to one key ingredient. Temperature contrast! We can all agree that cold air is dense, and that’s why it sinks. The opposite can be said about warm air, causing it to float above the cold air.

We can think of the Polar Jet Stream as a body of cold dense air moving very fast along the top of the Troposphere, and in doing so, carving a highway across the United States for all weather to follow along.

Ridges & Troughs

– StormTracker7 Ridges & Troughs Illustration

First we need to understand that Ridges & Troughs form as the Polar Jet Stream loses energy to push south and towards the equator, deepening our Troughs. This pattern is ever changing as we move through the seasons. In return this amplifies our Ridges, or builds them with warm air rushing in from the south.

Ridges, simply put, are warm moist air moving from the equator towards the north pole. Troughs are cold dense air pushing its way through the warmer air down towards the equator. All weather in the northern hemisphere moves from west to east.

It’s the interaction you get when the cold air associated with a Trough pushes the warm air up into the atmosphere, and eventually over top of the cold air where weather begins to occur.

Cold over warm indicates an unstable atmosphere, where as cold over warm air is standard, being that the Troposphere cools with height.

Air Masses

“Air Masses” – David Babb

All Air Masses have their geographic locations here in the U.S. as shown in the graphic above. To understand this graphic we must first think about the climate associated with these locations.

Typically, warm moist air is found along the Gulf of Mexico. This being known as a Maritime Tropical Air Mass.

Continental Polar Air Masses act as its rival. With extreme differences in these air masses, the meeting point in the central plains are where we find our most severe weather here in the U.S. Cold dense air from the north moves equator-ward, battling with the warm and moist air to find equilibrium.

Meteorologists track the wind speeds of the Polar Jet Stream to determine how strong of a cold push or Trough could develop. This will ultimately be the deciding factor in how strong of a weather system we could see. Tracking the pattern or road of the Polar Front Jet, Ridges, & Troughs allows for a better forecast, and understanding of weather here in the United States.