Winter Storms and Jet Streams
One of the vital ingredients for the formation of winter storms is the proper positioning of the jet stream.
The jet stream is an area of strong winds concentrated in a relatively narrow band in the upper troposphere of the middle latitude and subtropical regions of the Northern and Southern Hemispheres.
It flows in a semi-continuous band around the globe from west to east. The jet is the boundary between cold and warm air and it follows the warmer air.
Carl-Gustaf Rossby, a U.S. Weather Bureau employee (now the National Weather Service), first theorized about the existence of the jet stream in 1939.
However, it was U.S. Army Air Corps pilots flying B-29 bombing missions across the Pacific Ocean during World War II who proved the jet stream's existence. The pilots found that when they flew from east to west, they experienced slower arrival times and fuel shortage problems. When flying from west to east, however, they found the opposite to be true.
Exactly where in the middle latitudes of the Northern Hemisphere the jet stream can be found depends on the season. From December through February, the sun's rays are heavily concentrated in the Southern Hemisphere, causing the Northern Hemisphere to cool down. It is winter in the Northern Hemisphere and summer in the Southern Hemisphere.
During the winter, the jet stream continuously separates cold polar air masses to the north from warm tropical air masses to the south.
Therefore, during the Northern Hemispheric winter, the polar jet dips south across the lower third of the United States. The strength of these winds helps to bring colder air into an area of previously warm air and is instrumental in deepening low pressure systems.
Check out the various types of winter storms that form when the jet is involved and how forecasters use the jet when forecasting winter storms.