As El Niño gets stronger, we get drier

Since last month, ocean temperatures in the south-central Pacific Ocean near the equatorial regions have been warming up. It’s recently been confirmed that this abnormal climb of sea-surface temperatures has led to a weak El Niño phenomenon.

Most of our wet weather originates from the Pacific Ocean as these storms usually follow the upper-level wind-flow patterns. During many El Niño years, a strong ridge of high pressure will often block these Pacific storms from our region and direct much of the moisture south or underneath our area, particularly into California.

We’re already beginning to see this type of pattern as rain has been falling primarily in northern California and southern Oregon over the last several weeks. In fact, Sacramento and Chico, Calif., and Medford, Ore., have received more rainfall than us.

Elsewhere, the Phoenix area, the Mojave Desert in southern California, and even the Sahara Desert in Africa have measured more precipitaton than our part of the country.

June 15th through today, is now the second-driest period in the 126-year history of record-keeping at the Spokane International Airport, as we’ve measured .67 inches. Only 1925 was drier with .53 inches.

In Coeur d’Alene, this is the driest period ever recorded since 1895, as .89 inches has fallen. It’s so arid that area wells are now drying up and officials are still concerned that the tinder-dry brush could spark more fires.

Prior to this dry spell, we experienced the second-wettest spring. And from late December 2005 through late January, it was the wettest 30-day period on record in Spokane and surrounding regions. These back-and-forth weather patterns from wet to dry and vice-versa are part of our cycle of wide weather extremes that may be the worst in more than 1,000 years.

According to the National Weather Service in Spokane, when ocean temperatures are warmer than normal near the international date line in the Pacific Ocean, that blocking ridge of high pressure will often set up shop over much of the northwestern United State. Based on climatology and the latest computer model projections, this El Niño is expected to strengthen from a weak to a moderate warm-water phenomenon over the next few months.

The latest forecast, assuming that El Niño does slowly expand, now indicates that Spokane, Spokane Valley and Coeur d’Alene regions may see drier than normal weather between now and the through the first half of this upcoming winter. Our driest periods tend to occur during “weak” El Niños.

Temperatures may also be cooler than average as this area will be under a northwesterly flow from Canada. In order to receive bigger rains, we need a westerly or southwesterly flow from the Pacific as storms from the northwest are typically drier and cooler.

But, as El Niño strengthens and becomes more moderate in intensity, we should start to see storms eventually originate from the west and bring more much-needed moisture to our area. In other words, the second half of the winter season should be warmer and wetter, perhaps cold enough to produce snow in the higher mountains and hopefully salvage the local 2006-07 ski season. In the lower elevations, however, snowfall is expected to be rather scarce. During the last El Niño in 2004-05, Spokane received 25.8 inches, compared to a normal season of 41 inches.

Over the last five years or so, El Niños have been growing and falling apart in short periods of time. If this new warm-water phenomenon does weaken instead of expanding, we could expect conditions to turn considerably wetter and perhaps snowier sooner than later. However, I don’t see this happening at this point in time.

In the near-term, we should receive some moisture by Sunday and Monday. Our best chance to pick up decent amounts of precipitation would be next Saturday through Halloween, but the bulk of the moisture should again fall to the south of us. By early November, high pressure is expected to rebuild resulting in drier than normal weather. Stay tuned.