La Niña episodes are associated with three prominent changes in the wintertime atmospheric flow across the eastern North Pacific and North America.
The first is an amplification of the climatological mean wave pattern and increased meridional flow across the continent and the eastern North Pacific.
The second is increased blocking activity over the high latitudes of the eastern North Pacific.
The third is a highly variable strength of the jet stream over the eastern North Pacific, with the mean jet position entering North America in the northwestern United States/ southwestern Canada.
Accompanying these conditions, large portions of central North America experience increased storminess, increased precipitation, and an increased frequency of significant cold-air outbreaks, while the southern states experiences less storminess and precipitation.
Also, there tend to be considerable month-to-month variations in temperature, rainfall and storminess across central North America during the winter and spring seasons, in response to the more variable atmospheric circulation throughout the period.
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