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The Current Impact of the Jet Stream Is and Will be Felt

In a few articles, I’ve explained how much of an impact that the circumpolar jet stream has on the weather of the US. Since this jet stream circles the globe, it has the same sort of impact on Europe and Asia. A change in the Jet Stream recently gives a really good clue about the weather in the US through much of this week.

The jet stream is a current of fast-moving air, up to 250 miles an hour. It is typically a few hundred miles wide, rarely much more than 16,000 feet thick, and at a common altitude of about 6-9 miles (30,000 to 46,000 feet). The jet stream undulates up and down as well as north and south. Since the jet stream is marked by high winds and changes in air pressure, it can be plotted and this can be overlaid on a map, showing where it is at any given time.

Most of the weather that we experience is at a lower altitude than the jet stream. However, it has an enormous impact on the weather. Colder air is usually kept north of the jet stream and hotter air is normally found south of the jet stream.

It should be noted that I’m specifically referring to the north circumpolar jet stream. There are actually two jet streams in each hemisphere, north and south of the equator. However, it is the north circumpolar jet stream that has the greatest impact on North America, Europe, and Asia, so I’m referring to is as ‘the’ jet stream, even though there are three others at any given time.

The jet stream can vary in strength and wind speed, as well as its location. 

Currently, the jet stream is passing over the middle of Washington State and northern Idaho. From there, it is flowing almost directly over us in northwest Montana and it more or less is following the US-Canadian border. What does this mean?

Several days ago, our temperatures were in the mid 80’s (F) with sunny skies and afternoon thunderstorms. When the jet stream moved into its current place, our temperatures cooled to the low 70’s for high temperatures. It also brought in unstable air off of the Pacific, so we’ve had several rainstorms. Our high-temperature today isn’t supposed to get much above 72 F.

However, as the jet stream moves eastward, it is also undulating northward a little bit. Tomorrow, our temperatures should respond by reaching into the 80’s again. Then our temperatures should get hot; into the mid to upper 90’s or possibly over 100 F. To some people, such as those living in the southwest and deep south, this might not sound unusual, but keep in mind that we are only 60 miles south of Canada. Having temperatures approaching or exceeding 100 isn’t unheard of, but it also isn’t common.

The impact of the jet stream should also be felt throughout the continental US, with high temperatures and occasionally dangerously high temperatures in some locations, particularly the southwest and deep south. There is relief in sight, though. The jet stream should again veer south next week, which should bring cooler temperatures to the midwest and northeast. 

Not surprisingly, the fire danger in Montana was upgraded about four days ago from moderate to high. When the fire hazard reaches high, the forest fire season officially begins. Normally, that occurs in the last part of June, so it is late in getting here, though few people are complaining. Two years ago, major fires were already burning throughout Montana by this time of year and the hazard was extreme. Fire season began in early June that year.

This is to say that the jet stream even affects our fire season. At any rate, people in North America should brace themselves for the coming weather.

  • Question of

    Do you pay any attention at all to the location of the jet stream?

    • Yes, often
    • Not very often
    • Rarely or not at all
    • I didn’t know what the jet stream was before reading this
  • Question of

    Are you going to try to pay more attention to the jet stream in the future?

    • Yes
    • Probably not
    • My weather service doesn’t show what the jet stream is doing
    • I don’t care


What do you think?

15 points

Written by Rex Trulove

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  1. Nicely presented Rex. Not an easy topic, Most people don’t understand how a stream of air way up in the atmosphere can cause so much havoc.

    The current bump, the opposite (nearly) of the polar vortex is casing the massive heat wave.

    I watch the jet stream and do my own weather predictions!

    • I actually have fun making weather predictions, based primarily on the jet stream and the airflow maps. With the jet stream doing what it is doing, the air in the US and well into Canada, especially in the east, is surprisingly (to many people) stable.

      A big trough has formed in the Gulf of Alaska, though. When it moves it, it will probably miss us, for the most part, so our temps will still remain high and fairly stable. It should cool down everything east of the plains states, though. At the same time, I fully expect that there will be a large increase in unstable air and storms, especially thunderstorms.

      I’m still working on ways to illustrate how the airflow above most of the weather affects the air masses below it. I’ve thought of a number of ways to show it, but not everyone would be able to see it for themselves. You’re right, it is hard for a lot of people to visualize it and part of that comes down to two-dimensional thinking, in a different sort of way. Air that is moving at 1,000 feet is still connected to air that is moving at 5,000 feet.

      At the very same time, air acts fluidly in that the connection isn’t solid. Air at ground level can be moving at 30 mph to the southeast, for instance, while the clouds at 10,000 feet are being blown to the northwest; the exact opposite direction.

      Hey, maybe I could use the fluid analogy to help visualize what the jet stream does. After all, it does rather function like the bow wave created by a fast-moving ship. What do you think?

    • In your case, though the circumpolar jet stream can still definitely affect you, you are far enough south that the tropical jet stream also has a big impact. The tropical jet stream is far weaker than the circumpolar one, but it can bring you lots and lots of moisture.

      In the deep southeast, there can be clashes caused by the two jet steams forcing air masses together. That can result in massive electrical storms and tornadoes. It is one reason that more people are struck by lightning in Florida each year than in any other state.

  2. The jet stream is – as you say – hugely important to the weather we get in the UK, and its position is mentioned in virtually every TV weather forecast we get. There is a strong possibility that the more frequent fluctuations that have been noted in recent years are a result of climate change, and that this is therefore something that we will all have to get used to.

    • People haven’t known about the jet stream for that long; a number of decades, but in the US, the fluctuations haven’t been all that unusual. Considering that the climate has always been changing for quite a few million years, it is safe to say that the fluctuations are due to climate change, though.

      Winds are caused by uneven warming and that includes high-altitude winds. This has also probably been going on for millions of years, but I don’t know of any way they can study the jet stream from even a few million years ago, unfortunately. That would be fascinating.

      It is great to hear that your forecasts mention the jet stream frequently. Very often, those in the US don’t. I suspect that in large part that is because so many people have no idea what the jet stream is or does. A huge number of people don’t even care. They just want someone to tell them with certainty what the weather is going to be like in their locality, tomorrow or the next day.

      • Yes, the TV weather charts quite often show the current position of the jet stream and how it is bringing a polar or tropical airflow into play over the British Isles. Of course, because our climate is a maritime one, this rarely leads to extreme weather events. With your continental climate, however, it is a different story.

        • True, but the jet stream does have the same sort of impact inland to your east, though. Our inland weather can be very hot, like it is going to be for much of the US for the next few days, or tremendously cold like it was for much of the nation this past winter.

          The really whacky weather usually happens when the jet stream over the US is fluctuating wildly. This past spring, as one example, areas in Colorado experienced one day when temperatures were around 80 F/26.7 C and the people awoke the next morning to several inches of snow on the ground. (My cousin was living there at the time, though he just got done moving to Arizona in the past few weeks.)

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