Weather Moment: Cold Fronts

The weather effects each of us, every day.  A lot of people have expressed to me interest in learning about the weather, but it’s definitely not easy.  I’ve decided that each week, I’ll post a short-ish post explaining the basics of various weather phenomenon; this week: The Cold Front.

For many people, cold fronts are one of the most noticable weather events out there.  They are fast moving features that often produce severe weather and result in drastically different weather after they have passed through.

Formation

All over the globe, air has a tendency to form into large areas with similar characteristics.  We call these air masses.  One example is could be a large area where it is hot and humid.  In the wintertime, often there are extremely large areas of cold, dry air.  These air masses move through the atmosphere, and fronts are developed.  A cold front is the boundary on the leading edge of colder air moving into warmer air.  It does not matter how cold the cold air mass is or how hot the hot air mass is, as long as they have a temperature difference, the cold front will form.

Structure

Cold fronts have a very defined structure that is based on a simple physical principle: density.

Structure of a cold front.

From high school physics, we know that the density of a gas is defined by it’s temperature and it’s pressure.  Similar to how oil and vinegar have different densities, so do warm and cold air.  Cold air is more dense than warm air.  Because it is heavier, as the cold air (blue) pushes into the warm air (red), it begins to undercut the warm air and push it upwards at a very sharp angle.  This causes a very narrow, relatively intense band of precipitation to form along cold fronts.  Cold fronts move fairly quickly as the cold air digs underneat the warm air, and the weather associated with the front will be fairly short lived at any one location, usually lasting no longer than a few hours.

Common Weather

In the summer time, the passage of a cold front can often produce thunderstorms, or other significant weather features such as squall lines, supercells, and mesoscale convective complexes.  These are all different forms of organized thunderstorms that last for a very long time.  Due to the sharp upward push of the warm air, cold fronts can often produce short-lived, severe weather such as heavy rain with potential flooding, thunderstorms with large hail, and even tornadoes.  In the summer, cold fronts can offer a reprieve from hot, humid weather.  In the winter, the passage of a cold front can result in long stretches of cold weather and clear skies.

Next week, warm fronts.  If there are any questions regarding this week, just leave them in the comments!

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