RICHMOND, Va. (WWBT) - We saw this coming last week - a cool, cloudy, rainy pattern that would stick around for a while. Here it is on the water vapor map from the National Weather Service:
This is a classic example of a Cut-Off Low. Here’s the definition from the NWS’s online glossary:
“A closed upper-level low which has become completely displaced (cut off) from basic westerly current, and moves independently of that current. Cutoff lows may remain nearly stationary for days, or on occasion may move westward opposite to the prevailing flow aloft (i.e., retrogression).”
It’s called an upper-level low because it’s not at the surface. It’s at the jet-stream level (20 to 40 thousand feet up). I’ve drawn the upper low on the surface map below, which shows it’s displaced far the west of the surface low that’s set to bring us a round of soaking rain Thursday night and early Friday.
In this case, it’s a classic. The jet stream is displaced WAY to the North so the low has just been sitting and spinning...inching to the east and waiting for the jet stream to scoop it up and kick it offshore.
That kick is finally coming. This loop is a jet stream level forecast through early Saturday morning, showing a dip in the jet stream swinging in from the west. It’ll scoop up the cut off low and sweep it out to sea.
Just in time for the holiday weekend!
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