Monday, November 3, 2008

Air Masses and Fronts

I got away from the "daily lesson" in recent weeks just due to a hectic work life, but will attempt to get back in the grove.

This week we're gonna talk about air masses and fronts.

An air mass is an extremely large body of air where the temperature and humidity are similar as you increase with height or travel across the air mass.

So let's take a large, winter air mass that moves down from Canada across the lower 48 states.

It may have highs of -15 in Minneapolis with a dew point of -18, and in Little Rock it may have a high of +10 with a dew point of +7.

Although those temperatures are not similar as you travel the 1,000 miles across the air mass, both are very cold and very dry for the respected locations, and would be associated with the same air mass.

Now suppose Minneapolis is still -15 with a dewpoint of -18, but Little Rock has a high of 45 and a dew point of 38 -- the two locations would not be under the influence of the same air mass.

Minneapolis would be very cold and very dry while Little Rock would be cool but moist in that scenario.

Air masses originate in what we call source regions.

These are places that are typically flat, have light surface winds and a uniform topography and other characteristics -- i.e. deserts, the frozen arctic

Here in the much of the lower 48 where we live (also known as the middle latitudes (between 30 and 60°N on the globe) -- most locations are not good source regions because surface temperatures and moisture characteristics vary considerably.

We live in what is known as a transition region -- a zone where air masses with different physical properties move in, clash, and produce an exciting gamma of weather.

Tomorrow we will talk about the classification of air masses.

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