Here in the lower 48 states of America, we typically see a few different types of air masses impact our weather.
cP (Continental Polar) often visit during the winter. This air mass is sometimes called cA (Continental Arctic).
They usually bring bitterly cold weather.
These air masses originate over the ice and snow covered regions of northern Canada, Alaska and sometimes even Siberia.
Once an air mass slides south along the Rockies and enters the plains, there are no barriers to stop it -- so it moves all the way to the Gulf of Mexico.
Sometimes this is called a Texas norther.
Cumulus clouds are rare -- even during the warmest, most unstable part of the day -- because these air masses are dry.
At night, with clear skies and light winds, temperatures drop like a rock.
These air masses can make heavy snow when they move over a warm, large body of water, such as the Great Salt Lake or the Great Lakes.
These snow bands are common on the eastern shores typically when a large cP or cA air mass moves south and into the USA.
The Rockies, Sierra Nevada and Cascade mountain ranges usually protect much of the west coast from these bitterly cold air masses.
But if the right weather pattern sets up, they too can see the frigid air.
One very memorable arctic outbreak in the US took place between December 21-24, 1989. There were over 350 record lows set east of the Rockies.
$480 million dollars of damage was done to crops in Florida and Texas.
That same week in 1990, a bitterly cold air mass settled into the west, causing over $300 million dollars of damage to crops in California.
Lows dropped into the 20s all the down into the Los Angeles region. It was the coldest weather in over 50 years.
During the summer we look forward to seeing a large cP air mass move south out of Canada because they cool us down and lower the humidity for a few days.
Tomorrow we'll talk about maritime polar air masses. (mP)