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Major Factors for Cold
Outbreaks over US
qBuildup of a ridge in the jetstream level over western North America.
qFormation of a surface high-pressure center over northern Canada
or Alaska.
qMovement of the cold airmasses in response to steering by the upper-level winds.
qA mechanism to enhance the winds that transport the cold air southeastward. The triggering mechanism
is often a strong winter
cyclone crossing central or eastern North America.
qExtensive snow cover over central North America to keep the polar airmasses “refrigerated”.