GREAT FALLS — The El Niño Southern Oscillation, or ENSO, is now in its La Niña phase for the second winter in a row. The climate oscillation takes place in the central and eastern Pacific Ocean, adjacent to the equator.
There are numerous, naturally-occurring climate oscillations that take shape throughout our planet. Generally, the oscillation has a positive, negative and neutral phase. The positive phase being an area of above normal sea surface temperatures in a given area and the negative phase being an area of below normal sea surface temperatures in that same area. This diversion from that area's normal sea surface temperature has regional, if not global, implications on climate. The phases typically last a few months to as long as several years with ENSO's phases regularly lasting 1-3 years.
Trade winds typically blow from east to west in the central and eastern Pacific, where ENSO takes place. This pushes warmer than normal ocean waters to move westwards towards Asia. During a La Niña phase, trade winds are stronger than normal giving way to increased wave activity and mixing of water at different depths from the surface. This mixing brings cooler water closer to the surface.
The El Niño Southern Oscillation has the most prevalent effects on United States' winter. A moisture feed, namely the Pacific Jet, sets up bringing wetter than normal conditions to much of the Pacific Northwest. Outside of the extreme western part of the state, La Niña's impact on Montana precipitation is relatively minimal. With that said, it has significant implications on our wintertime temperatures. The Polar Jet sets up almost directly over the state and this leaves the door open to multiple shots of frigid, Arctic air to pour down from Canada.
For the Southwestern United States, La Niña provides a drier and warmer than normal winter. With the mid-Atlantic United States and New England experiencing snowier but warmer winters. The impacts of ENSO are not confined to winter, the oscillation has impacts during the hurricane season and even influences the monsoon season in the Southwestern United States.
