Chances are low for more ‘heat waves’

SUNDAY, AUG. 22, 2010

If you are a hot weather lover, hopefully you enjoyed the past week of sunny weather with highs in the upper 80s and lower 90s. Currently, average highs are in the low to mid 80s, while average lows are in the mid 50s. While temperatures still may spike up into the 90-degree range through early September, chances are low we’ll see any more extended “heat waves” in the coming month. Triple-digit heat has eluded us this season, and this summer’s “heat waves” were pretty mild, relatively speaking. Spokane saw consecutive days of 90-plus degree temperatures only twice, back on July 25-26, and most recently Aug. 16-17. Coeur d’Alene was slightly warmer, seeing two-day stretches of 90-plus degree temps on July 8-9, 24-25, 28-29, and a three-day stretch Aug. 15-17. The highest temperature recorded in both Spokane and Coeur d’Alene this summer was 96 degrees.

I mentioned in a previous column that we are now officially in La Niña, a period where the waters in the equatorial Pacific are cooler than normal. Locally, this usually means wetter and cooler weather across the Northwest during the winter season. But just how are sea surface temperatures measured, and what are some other major signs that the tide has turned to La Niña?

La Nina is actually part of a larger cycle called ENSO for El Niño/Southern Oscillation, which involves complex interactions between the oceans and the atmosphere. During La Niña, the trade winds – the prevailing pattern of easterly surface winds in the tropics – are unusually strong. These winds serve to actually “push” the ocean water westward, resulting in upwelling along the South American coast. Though this upwelling occurs during neutral years, it is enhanced during La Niña, resulting in the colder than normal surface waters over the eastern tropical Pacific. While the eastern Pacific sees the colder water, the western Pacific is warmer than normal resulting in more storms and sometimes destructive flooding. There is also an increased frequency of typhoons (hurricanes) which hit the coast of Japan, Korea and Australia. The cooler water in the eastern Pacific, however, causes the rains to “dry up” along the coastal regions of Peru and Chile, leading to drought.

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