What’s holding up the cool-down?

To get cooler air to move our way, we basically need a good push on a cold front. If the push is strong enough, it will drag in some much cooler air from Canada down our way. The “push” on the front is usually in the form of north or northwest winds. The stronger the winds, the farther away the air that they typically tap into, so a strong push of the front will typically usher in the coolest of the air from the north.

But what gives any cold front a push? Take a look back at my blog post titled, “What is a disturbance?”, to see what these weather disturbances look like in the atmosphere. Here’s a look at what the pattern should look like a little bit later this week:

Upper-level pattern showing a "cut-off low" this week near Utah/Colorado border.
Upper-level pattern showing a “cut-off low” this week near Utah/Colorado border.


The cut-off low pattern that shows up a little west of Kansas by Wednesday will very slowly slide east. Think of this as a very slow-rolling bowling ball as it moves toward us. (You’ve bowled with a 5 year old, right?) Ahead of it, the air is rising, which will trigger showers and storms. The best chances for this for our side of Kansas will be as it draws closer to us by Thursday night through Saturday. Once it passes, the rain chances will let up.

But what about the cooler air? Sure, it will cool down when you add in more rain and clouds to the picture, but what about a real cooling? This one doesn’t look as promising because it’s not getting that push on it. Why? One main reason is that it’s no longer attached to the jet stream. It is a “cut-off low.” These lows move notoriously slow and have little push on them from cooler north winds. The jet stream is what typically separates the cool air to the north of it from the warm air to the south of it. Since this system is cut-off to the south, it is mainly surrounded now by fairly warm air.

The jet stream typically separates warm and cool air in the Northern Hemisphere.
The jet stream typically separates warm and cool air in the Northern Hemisphere.


So, this turns out to be a case of give a little, take a little. We get to take a few more days of rain chances by having this system move at us much more slowly, but we have to give up the cooler weather that once looked to come with this same system because it decided to cut-off and part ways from the jet stream. Don’t worry, the two seem to make up and the system will rejoin the jet stream to our east a couple days later.

Storm Track Chief Meteorologist Matt Miller

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