Waves in the jet stream bring changing weather

Published 7:00 am Saturday, December 12, 2020

By Skip Rigney

Four fast moving waves of low pressure up at altitudes where the jets fly will bring us a roller coaster of changing weather over the next week.

The jet stream winds five miles above the earth’s surface are blowing even stronger than usual from west to east in a huge river of air encircling the northern hemisphere.

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When the jet stream winds circling the globe are this strong the wiggles in the jet stream tend to be smaller. That means that the really cold air stays bottled up at northern latitudes rather than plunging south, and warm air doesn’t rush too far north. So, most of the air that will move through our region during the next week is coming from over the Pacific Ocean instead of the bitterly cold regions in the Arctic.

Even though there aren’t any major north-south curves in the jetstream predicted over the United States by the computer weather models in the upcoming week, there will still be a number of smaller waves moving along the southern edge of the jet stream. It’s those smaller waves that will be the source of our changing weather this week.

The first wave passing by to our north will cause some showers this morning (Saturday), then drive a surface cool front through south Mississippi later today. But, the cool front won’t make it very far to our east and south before it feels the tug of a second wave in the jet stream racing eastward from the Texas Panhandle by Sunday morning.

This second wave in the upper-level winds will pull moisture from over the Gulf northward, so expect a chance of showers Sunday afternoon and an even higher chance Sunday night.

The second wave and an associated cold front will pass to our north and east on Monday morning. Even though the air in its wake is coming from over the Pacific and not northern Canada, it will still be noticeably cooler.

We probably won’t make it any higher than the middle 50s on Monday afternoon, which would be the coolest daytime maximum temperatures we’ve seen so far this December.

The third in the fast-moving train of jetstream waves is predicted to pass to our north through Arkansas on Tuesday night. Ahead of the wave, the chance of some light showers will return on Tuesday afternoon or evening.

We will be on the backside of this third wave by Wednesday morning, which will mean another spell of brisk, cool northwest winds with temperatures starting the day in the 40s and not getting out of the 50s. Frost and perhaps a light freeze are expected Wednesday night as calm winds and clear skies create optimal cooling conditions.

Thursday and Friday should be cool and dry with mostly clear skies as a ridge of high pressure stretches all the way from eastern Canada down across the southeastern United States and into the northern Gulf of Mexico.

But, by next Saturday the computer models hint that a fourth wave in the jet stream wave train may be approaching from the west.

It’s too far out to accurately forecast the timing or the amount of rain, but it looks like rain chances will return again to our area for at least part of the last weekend before Christmas.