La Niña “Watch” issued for upcoming fall and winter

Phenomenon increases chances for heavier winter snowfall

La Niña “Watch” issued for upcoming fall and winter
La Niña could increase chances for a colder and wetter fall and winter in the Northwest (KIRO/KIRO)

It seems we’ve hardly had much “summer” yet in Western Washington, but already we’re looking ahead toward the upcoming fall and winter, trying to divine any trends towards either a drier or wetter (and colder) winter.

Recently, colder-than-normal waters have been observed off the west coast of South America, along the equator. This is the region we look at for the ENSO signal -- which stands for El Niño Southern Oscillation. That is the back-and-forth warming and cooling of waters that gives us El Niño or La Niña.

The temperature of that patch of water tends to affect the jet stream patterns across North America, which then directs storm systems.

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Those cooling waters look as if they could persist into the end of 2020, which could lead to a La Niña fall and winter!

Thus, NOAA has issued a “La Niña Watch” for the fall and winter, as the chances of a La Niña fall and winter is greater than 50/50 (but only slightly above that level.)

It is very important to remember that the predictions for ENSO are not foolproof and even if El Niño or La Niña occurs, there’s no guarantee it would have the expected effects on our weather in the Pacific Northwest.

Still, if La Niña does occur, it could lead to an increase in storminess here in the Northwest, with a greater chance of above-normal mountain snow and a somewhat increased likelihood of lowland snowfall events.

Think of La Niña as “weighting the scales” a little toward cooler, wetter and possibly stormier weather patterns late in 2020 and early 2021.

It’s too early to get too excited about this as there have been sudden switches in the ENSO pattern. Once we get to about September, we’ll have a much greater confidence in the ENSO state for the fall and winter -- about the time folks lock in those ski season passes!

Rest assured, we’ll be watching this and tracking it on KIRO 7 as conditions change.