Patrol Weather question of the day.

What influences does El Nino have on the weather pattern of the PNW?

During El Nino years, the storm track more frequently splits into two preferred branches. The Aleutian Low, in the Gulf of Alaska, is deeper than usual, and one branch of the jet stream departing from its vicinity heads toward the Queen Charlotte Islands and the southern coast of the main part of Alaska, bringing mildly increased storminess to those areas. A second branch of the jet stream is seen across the southern tier of the U.S. and northern Mexico, and with higher speeds than usual. Storms approaching the Pacific Northwest, and southwest Canada, are often split and weakened as they approach the shore, as their energy is shunted toward the north and/or the south.

The Pacific Northwest, El Nino tends to bring drier winters. The area affected in this manner includes Washington, Oregon, and the more mountainous portions of Idaho, western Montana and northwest Wyoming. This area of influence extends well up into Canada, and coincides very well with the Columbia River Basin on both sides of the U.S./Canada border.

La Nina:  La Nina generally brings cold, snowy, wet, active winters to the northern Cascades and the northern Rockies. There are a few exceptions to this picture among La Nina years. There appear, however, to be more such exceptions in El Nino years, to the dry, mild winter pattern these regions typically experience with El Nino.