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What's Causing Our Constant Sunny, Warm Weather?

Published On: Feb 25 2013 07:21:03 PM CST

This year, the Northstate has had beautifully warm, but dry weather.

Currently Redding is nearly four inches below normal for the wet season, which began last July.  However, Redding is just over nine inches short of its average rainfall since January 1.

All of the dry weather is caused by natural phenomena and large-scale weather patterns in the upper levels of the atmosphere.  In short, it all comes down to the jet stream.

So what is the jet stream?

The jet stream is a river of air in the upper levels of the atmosphere.  It is caused by the interaction between the warm air in the south and the cold air in the north.  Where they meet, the temperature difference pushes the wind speeds higher and higher.

The jet stream is the strongest in the winter months because that is when there is the greatest difference in temperatures from the tropics to the arctic. 

The interaction between these two air masses causes all the storm systems which bring the Northstate its winter rain and snowstorms.

You can think of the jet stream as a roadway – one that is rarely stationary.  It is constantly wiggling north and south, bringing warm air from the tropics to the northern latitudes, and cold air from the arctic southward.  This movement causes the storms which bring us rain and snow.

This year, the jet stream has been stuck in a specific pattern.  That pattern has kept a very strong ridge over the western half of the country.  That means that the storms ride along the jet stream around northern California, missing the north and keeping the Northstate sunny, dry and warm.

From there, the storms travel across the Rocky Mountains into the central United States.  There, the storms gather energy as the cold air over the Great Plains meets the warm moist air from the Gulf of Mexico.  When those two air masses meet, it causes the storms we have seen in the rest of the country.

Northern California has seen this very strong ridging pattern over the last few months and long range forecasts don’t indicate it weakening any time soon.  Climatological models are forecasting a below-average rainfall for the next three months. 

The lack of rain has prompted a drought development forecast from the National Weather Service’s Climate Prediction Center.