The northern jet is the dominant jet in this animation, courtesy of U.S. taxpayers and NOAA's Air Resources Laboratory. The highest wind speeds (>=70 kts) are shaded in blue and the southern jet shows up in the last few frames.
What you see happening here is called a "cutoff low" by meteorologists. Literally closed lines (contours) form which encirlce a pool of cooler airupstairs. Cool air upstairs also indicates low pressure, in this case betweent 35,000' - 40,000' above sea level. The cutoff low basically spins in place or as I often say treads water above us and does not go very far very f ast becasue it is isolated (i.e. cuttoff from) the main jet stream flow.
And because it is a low pressure system air is rising inside the cutoff low and that lift generates showers and clouds. So under a cutoff low or a "slow low" as some call it, for several days showers are possible along with cloud cover and cool-ish weather.
The video below has more.
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