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Two jetstreams phased as one


If you paid much attention to the forecast over the last few days, you've likely noticed the big drop in temperatures expected later this week. That may be about the only thing that is fairly certain.

It looks very likely that we will have much colder air not only move in, but settle in for the second half of the week and the weekend.

In the map above, you can see how both the northern branch (the Polar Front Jetstream) and the southern branch (the Subtropical Jetstream) phase together right over Kansas later this week and into this weekend.

So what does that mean? Well, very often with the phased jet, the movement of storm systems is very quick across the middle of the country. That means that any disturbances capable of producing some snow in the colder air would likely not last too long and would not be able to be projected as much in advance as usual.

Because the subtle changes in the jetstream (called shortwaves) are an important driving force in the overall weather pattern, tracking these is a core aspect to weather forecasting. These fast-moving shortwaves are more difficult to discern in this pattern and we end up with much less "heads-up" for weeks like this.

So here's the bottom line: With a cold weather pattern shaping up for the latter part of the week, it is likely that one of the shortwaves will provide enough lift to the area to produce some precipitation. Whether that occurs Sunday or into early next week is the bigger question that we'll have to hold off a bit longer to see how the pattern develops. This phased pattern is still in its early stages.


Erin Graham 8 years, 4 months ago

Didn't the 1993 'super storm' in the east have something to do with jet convergence? ...but with everything shifted a little SE...a stronger sub-tropical flow pulling in more moisture from the gulf, a very deep cutting polar jet over the midwest and throw in a cut-off low or two?

(no implications. just remembering, I think a 500 mb chart i saw once... maybe that's completely off?)

bearded_gnome 8 years, 4 months ago

These fast-moving shortwaves are more difficult to discern in this pattern and we end up with much less "heads-up" for weeks like this.

---but I thought we'd closed down Club 8-2-1!

Mark Zwahl 8 years, 4 months ago

Thanks Matt. I appreciate this kind of information about the world we live in.

mwmiller 8 years, 4 months ago

Bob - sorry about the formatting.

wxbuggin- You are correct. The significant trough in the polar jet dipped down through the Midwest into the Southeast and was aided by the subtropical jetstream to build the 1993 storm. Good recollection!

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