Monday, April 7, 2014

The amazing power of the cold air wedge

We talked for several days about the revved-up weather that we were expecting today. It was to be a one-two punch of heavy rain in the morning and then severe storms in the afternoon and evening.

The first part developed pretty much as expected.  But the severe storms apparently will be a no-show for the Charlotte region.

And it's all because of the amazing power of the cold air wedge.

A quick review ... the cold air wedge is the name given a condition in which cool air becomes trapped in the Piedmont and foothills of the Carolinas and Virginia.  Typically, an onshore wind brings the cool air into the Carolinas. Since cold air is heavier than warm air, it sinks -- and becomes trapped against the mountains.

Sometimes we get what's called an in-situational cold air wedge.  The air is relatively cool and quite dry. Then precipitation from a low pressure system arrives. As it falls into the dry air, it cools temperatures even more.

Often in these situations, a warm air mass is lurking somewhere to the south or southeast. Occasionally, a warm front plows into the cold air wedge and erodes it.  Usually, the cold air wedge holds on. When that happens, Charlotte is stuck in the soup, with chilly, damp conditions.

Weather computer models frequently err in predicting the erosion of the wedge. They tend to forecast the wedge will break down, but that often doesn't happen. Today is the latest case in point. The warm air that several of the models predicted would reach the I-85 corridor by Monday afternoon hasn't even pushed west of I-95.

The cold air wedge is a real pain for meteorologists, whose forecasts are busted when the warmer air never arrives.  Charlotte was supposed to have reached the middle 60s by late Monday afternoon. Barring something unexpected, temperatures will remain stuck in the lower 50s.

At 3 p.m. Monday, it was in the upper 70s along the coast and about 40 miles inland. Temperatures were 30 degrees colder along the I-85 corridor. And to the west of the mountains, temperatures were in the low and mid 60s, on the other side of the trapped air.


Anonymous said...

Please let there be drought.

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