BLOG: What kind of cold front doesn't bring cold air? - | WBTV Charlotte

BLOG: What kind of cold front doesn't bring cold air?

CHARLOTTE, NC (WBTV) -

We have a cold front approaching the Carolinas today… but today’s high and tomorrow’s high are going to be about the same. How can that be?

Well, the term cold front isn’t all it’s cracked up to be.

It’s a boundary between two air masses. The air mass in place is warmer and more humid than the one moving into it. However the temperature difference can be very slight.

Sometimes it isn’t even noticeable to most of us. There are other things that go along with a frontal passage that will signal it has passed.

The winds switch direction, the pressure falls and the humidity drops behind the front. There can also be clouds and rain. There is a temperature drop – even if it is only slight and only drops briefly.

The change all has to do with what kind of air mass is moving in compared to the one that has been in place.

An air mass is a big heap of air that forms over a source region. If it forms over the polar region, it will be very cold and dry - because the poles are very cold and dry.

If it forms farther south, over the US, it won’t be as cold. Sometimes, an air mass can even form over a really cold region but if it moves very slowly or stalls over a region that is warmer, it will begin to take on the characteristics of the new region.

By the time is reaches us here in the south, it can be totally different from when it originally formed.

When a new air mass comes in, the two air masses don’t just mix though. The colder air pushes into the warmer, less dense air and causes it to rise. That boundary is the front, itself.

Today is one of those atypical examples.

Our weather has been very mild for December.

The warm and more humid air mass is in place. Late today, a new air mass will arrive. While it’s a little cooler and a little less humid, it didn’t form over the Arctic so it isn’t terribly cold.

In fact, the air behind the front is also rather mild. The coldest air will stay to our north.

Still there is enough of a difference in air masses that there is a frontal boundary.

When it comes through, there will be a wind shift, a slight (and temporary) temperature drop, the humidity and the pressure will drop.

That’s also why we have rain chances today until the front moves through. After it does, we will clear out and dry out tonight.

The sun will return behind the front on Tuesday. The temperature won’t change much but the humidity will be lower. The winds will be out of the south before the front moves through and then will shift to a more westerly direction afterward.

So, we still have to wait a few more days for more typical Christmas weather – but at least you learned a little about cold fronts, right?

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