It is no secret, Kansas weather can be extreme at all times of the year, but we tend to notice it more in the fall, winter and spring months. Over the month of October, we had some large swings in daily high temperatures in the Wichita area. A daily high of 96 degrees was recorded on October 9, and just a few days later we were in the 70s. Large swings in a short period of time are common.
The basic answer as to why this happens is the active jet stream this time of year. You have probably heard the term “jet stream” thrown out often, especially in relation to air travel. The jet stream is a band or river of strong winds in the upper levels of the atmosphere. These winds are typically found at the top of the troposphere, which is the lowest layer of the atmosphere where all of our weather occurs and the layer we live on. It is found between six and nine miles above us which is typically where planes fly. If planes are flying with the jet stream at their back, the flight is much quicker and fuel efficiency is higher. Think about a tailwind in a car, except jet stream winds can reach upwards of 275 mph!
The jet streams we have in the earth’s atmosphere generally follow the sun. This means as the earth tilts towards the sun and the northern hemisphere heats up, the jet stream retreats farther north. The opposite happens in the winter as the northern hemisphere tilts away from the sun and we begin to cool, the jet stream ventures south. As the jet dips south, we begin to encounter big temperature swings in the mid-latitudes.
These jets form on the boundary of contrasting air masses, or big swings in temperature. The temperature between air masses varies the greatest in the winter months, which further enhances the jet. Jet stream winds often strengthen with greater temperature differences. A strengthening jet stream can often lead to weather impacts at the surface.
We have two types of jet streams in each hemisphere, the polar and subtropical. The polar jet stream most commonly influences the United States, while the subtropical jet stream stays a little farther south and is a bit weaker. The polar jet stream becomes more active in the fall, winter and spring months before quieting down in the summer as the temperature difference generally lessens.
These rivers of strong winds in our atmosphere can have big impacts on weather at the surface. Where the winds are the strongest, we can get “jet streaks” that help aid in storm and cloud formation. Strong winds in the upper levels can help create storm systems, clouds and bigger temperature swings on the ground level. These strong winds also steer our weather systems, like a large area of low pressure, a hurricane or a nor’easter. The jet stream is also important as it helps our weather patterns efficiently move from west to east over the country.
Listed below is an example of how a small dip in the jet stream can quickly amplify. As mentioned before, this happens due to big ranges in temperature creating stronger winds. As winds get stronger, they can further amplify the jet stream and channel colder air farther south. Temperatures and jet stream location/strength are hand in hand. As large troughs (dips in the jet stream) form and cooler air invades, the warmer air has to go somewhere. Oftentimes, ridges (rises in the jet stream) occur as a result. This can bring warmer air farther north in front or behind the trough. This type of setup below is typical when polar air surges in during the winter months.
Right now, the jet stream is now retreating farther north, so we can expect many more active swings in temperatures as we head into late fall and early winter.
-Meteorologist Warren Sears