November 03 / News

Looks like La Niña Will Visit the US this Winter

Winter white forest panorama with snow, Christmas background


Forecasters are predicting an 85% chance that La Niña could last through the winter and a 60% chance it could last through spring of 2021. This weather phenomenon is something that could contribute to increased chances of flooding.

What is La Niña?

La Niña occurs when the tropical ocean waters near the equator of South America are colder as a result of stronger than normal trade winds pushing the warm water west towards Asia. The cold waters from the deeper parts of the ocean flow upward and the jet stream moves further north than its normal path. When this happens, usually the Pacific Northwest part of the country gets heavier than normal precipitation that often leads to flooding.

La Niña FAQs:

  1. La Niña typically peaks during the winter months in North America.
  2. La Niña episodes typically last nine to 12 months, but some prolonged events may last for years.
  3. While their frequency can be quite irregular, El Niño and La Niña events occur on average every two to seven years.
  4. Typically, El Niño occurs more frequently than La Niña.
  5. During a La Niña year, winter temperatures are warmer than normal in the Southeast and cooler than normal in the Northwest.

Video from NOAA

What does this mean for flooding?

Pacific Northwest

Typically during a La Niña year, the Pacific Northwest gets hit with higher than normal precipitation. This increased wet weather may bring about flooding from La Niña’s increased rainfall. Heavier snows may also increase flood risk during spring snow melt.

  • In areas where fire ravaged the land, this creates an even greater risk for flood in that the land no longer has the vegetation and soil to hold and absorb water.

Download La Niña in the Northwest 1-Page Handout

Midwest

The Midwest may also be at an increased risk of flooding during a La Niña year since it’s anticipated to bring about more rain and snowfall in certain parts of the Midwest.

  • Spring river flooding that is all too well-known in this part of the country could become more intense with La Niña.

Download La Niña in the Midwest 1-Page Handout

Southwest

With La Niña, the Southwest often is dry. This is not a good combination in our already drought and fire-ridden locations. This could perpetuate even greater drought-like conditions that could blow up the 2021 fire season.

  • Areas stripped of all its vegetation and soil from fires are at an increased risk of flooding for years until the vegetation starts sprouting back to life. Hardpan ground that doesn’t absorb water sets the stage for flash floods when the rains do eventually make their appearance.

Download La Niña in the Midwest 1-Page Handout

Sources:
https://www.climate.gov/enso
https://www.pmel.noaa.gov/elnino/laNiña-faq
https://www.climate.gov/news-features/blogs/enso/october-2020-la-ni%C3%B1a-update