Saturday, May 4, 2013

Central U.S.: Why is it So Cold?

From a reader request: Why is it so cold in the central U.S. right now?

The reason is a low pressure system about three miles up in the atmosphere that is "cut off" from the usual winds that force a low to move from west to east. This low is so strong is "manufactured" its own cold air by forcing the air to rise (air cools at a rate of 5.5°F per thousand feet of ascent).

While the map above is of the upper atmosphere, the ground level temperature map reflects the influence of the low. I have added arrows to show the air flow.

It is nice and mild over the Ohio Valley with southeast winds ahead of that low. Because the low is "cut off"it is going to be slow to leave.

By the way, 40°F and drizzle at the Smith House at 9am.

ADDITION: See Richard's comment below for the animated version. Here is the wind map he mentions. I added the arrows. Thanks, Richard!

1 comment:

  1. For a fascinating "live" view of winds across the U.S., go to:

    The low pressure system shown graphically above almost springs to life.


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