La Nina lingers — and what that portends

The cooler-than-normal sea-surface temperature event, La Nina, has been with us since late 2021, and according to the National Oceanic and Atmospheric Administration, weather patterns have been strongly influenced by this phenomenon.

La Nina is the abnormal cooling of ocean waters in the south-central Pacific Ocean, while El Nino is the abnormal warming of sea-surface temperatures.

Within the last month, it appeared that La Nina was showing signs of weakening as warmer-than-normal ocean temperatures were forming near the west coast of South America. La Ninas and El Ninos will often form along the equator, especially near the South American coastline. However, sea-surface temperatures have cooled down once again, with some areas around 4 degrees below average levels.

Ocean waters are still warmer-than-normal in the waters north of Hawaii and along the U.S. East Coast. In fact, there has been a large expansion of the warmer-than-average sea-surface temperatures north of the Hawaiian Islands.

Readings in this region are 2-5 degrees or more above normal. This area of warmer waters may also enhance the high-pressure ridges that form off the coast of the western U.S., especially later this spring and summer, resulting in drier and warmer than normal weather.

Australian forecasters watch the warming and cooling of ocean waters very closely as their weather is strongly influenced by these patterns. For example, during El Nino years, conditions in that part of the world turn much drier. During the last El Nino episode, there was extensive drought across the Australian continent that led to disastrous wildfires. However, when La Nina formed, many areas went from drought to floods.

Australian forecasters did confirm that this La Nina phenomenon was “easing” in April, and the trend is expected to continue based on their outlooks. However, that scenario may change as there has been a strengthening of this phenomenon within the last week to 10 days.

Australian forecasts see La Nina holding on through the summer season and continuing its influence on global weather patterns. Based on the current pattern, the chances are better than 50/50 that La Nina will be a factor into the fall season.

According to NOAA’s Climate Prediction Center, another organization that watches sea-surface temperature patterns, La Nina is likely to hang on through the end of this year. Many computer models are showing a slight easing, or warming, of the region later this year, but the influence of the cooler waters should persist.

Based on historical and climatological data, late spring and summer patterns are expected to turn much drier and warmer than normal across much of the western U.S., including the Inland Northwest. Forecasts from NOAA are also showing this pattern developing across our region.

We’re already seeing drought conditions in the West extending into the Great Plains, mainly west of Interstate 35. With the drier weather in the Southwest, major wildfires have already broken out across Arizona and New Mexico. Assuming La Nina hangs on, the drought pattern may expand farther to the east later in the spring and summer months.

As I’ve mentioned in previous columns, within the last 10 years, many of our spring moisture seasons have been near or above-normal levels. Then, the summers turn drier than average with long stretches of days without any measurable rainfall. With forecasts of above normal temperatures this summer, it’s very possible that we’ll see at least several days with highs at or above the 100-degree mark in Coeur d’Alene. Once again, it may be another tough wildfire season across the western U.S., especially in California.

Speaking of California, the Golden State has seen some much-needed moisture in April with snows in higher mountains. Despite the wet April, California will have its third year in a row of drought as recent moisture wasn’t nearly enough to make up for the moisture deficits.

Despite recent snows in the Sierra Nevada mountains, snowpacks are only around 30-35 percent of normal, with many reservoirs near 50 percent of capacity. Over the last 20 years, the western U.S. has likely seen the worst “megadrought” in over 1,200 years.

Local weather

In terms of our near-term weather, Cliff and I still see precipitation across the Inland Northwest to be near to above-normal levels through at least the middle of the month. It’s also possible that some of this moisture could make it down into northern California.

After the longest stretch of cold weather in April’s history, temperatures in Coeur d’Alene and surrounding regions should be turning warmer with highs climbing into the 70s over the next several weeks. However, there will still be instances when readings will be chilly as Pacific storms briefly usher in cooler air masses.

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Contact Randy Mann at randy@longrangeweather.com