The National Weather Service says the Northwest should expect a warmer and drier than average winter in 2006-07, courtesy of a new El Nino brewing in the equatorial Pacific.
The NWS' Climate Prediction Center issued the news Sept. 13, after four straight months of conditions that have signaled warming in the tropical Pacific. It's latest forecast calls for the warm episode to last into next spring.
The last major El Nino began in April 1997 and continued through May of 1998, with two other lesser events since then, the last between June 2004 and March 2005.
The announcement comes on the heels of good news from the University of Washington, which reported that the index which tracks the Pacific Decadal Oscillation took a big dip into negative territory last month, which generally means a trend toward wetter, cooler ocean conditions that are good for fish and umbrellas. But with a weak to moderate El Nino on the way, the U.W. researchers say the PDO index is likely to go positive soon and stay that way for the next few seasons.
"The unusually fair weather pattern has also included stronger than average coastal upwelling for Oregon and Washington, and coastal ocean temperatures in August were generally 1 to 2 degrees C below the long-term average from extreme Northern California to Vancouver Island," according the UW Climate Impacts Group.
NOAA's National Climatic Data Center reported that Northwest temperatures for May-July 2006 were the warmest on record (June-July-August was 3rd warmest for the PNW on record), and the first seven months of 2006 was the warmest January-July of any year in the U.S. since records began in 1895.
As for just how much rain is expected, the government is hedging its bets, noting that in the absence of strong El Nino or La Nina conditions, precipitation forecasts are "marginally skillful."
The Oregon Climate Service at Oregon State University expects warmer than average temperatures, average to somewhat above-average precipitation, a good chance of one or more significant snow events in the Portland area (less likely elsewhere in western Oregon), and an average snowpack in the mountains (possibly higher than average in southern Oregon).
But the Oregon forecasters said that "a sustained warming beginning in August or September would be unusual, given that ENSO events typically begin to evolve between March and June. Our forecast favors a continuation of the current neutral-to-slightly-El Nino conditions. If the Pacific reverts back to weak La Nina conditions, a much wetter winter is likely - similar to last year."