Update: NOAA Says La Nina In Full Swing Now
2:30pm Thursday, August 5th 2010
NOAA issued it's latest update today, which indicates that La Nina will continue to strengthen this coming fall and winter. You can read the entire NOAA update at the link below, along with my personal thoughts on the impact to our area below.
http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.html
La Nina = Portland / Vancouver Could See A Wild Ride This Winter
* Note - The views presented below are my personal assessments. I am not associated with NOAA. Permission is granted to quote or reuse the information below, with credit given to author.
Headlines
"Get ready. Mother nature has decided to toss us a La Nina curve-ball, which could equate to a wild ride for the Pacific Northwest this winter. Last winter was dominated by an El Nino which directed much of the colder and wetter weather away from the Pacific Northwest. This coming winter may not be as lucky. Opposite of an El Nino known as La Nina, is marked by colder than normal ocean temperatures along the equator that wax and wane on average of every five years or so. These fluctuations help steer the jet stream across the United States during the northern hemisphere winter. However, the devil may be in the details this year. The current La Nina episode is not only the second event in just the past three years, but also shows signs of being just as strong as the last. This year's La Nina also came on very quickly, which may have contributed to what was a dismal start to summer, with record setting rain and cold weather in both May and June. The Portland airport has only reached 90 degrees or higher four times this summer which is well below normal. This summer has also been marked with a greater than normal number of cloudy mornings before finally see sunshine in the afternoon. This has also helped keep high temperatures down this summer west of the cascades.
La Nina Can Be Wild
The previous La Nina lasted from 2007 through 2008. During that event, the coast suffered through a prolonged wind storm not seen there in decades. Winds were clocked at more than 125mph at several coastal location from Lincoln City north to the southern Washington coast and stayed at or above hurricane force in some locations for more than 36 hours. Record setting floods struck western Washington that winter as well. In December of 2008, the Portland airport received the most snow in December history (1940-present), along with its whitest Christmas on record. Nearly 10" was on the ground over Christmas, smashing any previous records held. Winter of 2008/2009 went on to be the snowiest in Portland since 1968/1969 with 24" and 34" respectively.
This Year's La Nina Is Different
This years La Nina is also occurring at a very interesting time when two other "x-factors" may be coming into play as well. X-factor #1, widely known as the PDO (Pacific Decadal Oscillation) which oscillates every 25-30 years has flipped back to the cold phase in the last few years. The PDO is essentially a method of tracking sea surface temperatures in the North Pacific and Gulf of Alaska. The PDO phase can also have an impact on jet stream patterns specific to the Pacific Northwest. A rare weather "treat" is when the cold phase PDO is coupled with a global La Nina. These two phenomenon, when combined have been known to bring the Pacific Northwest some of its wildest winters, with plenty of snow, especially in the mountains. The Pacific Northwest last saw a prolonged cold phase PDO signal from roughly 1950-1975. X-factor #2 is that all of this is occurring at the same time as the sun continues to rest in a deep solar minimum, not seen in the last 100+ years. The sun naturally fluctuates in the amount of solar output every 11 years, in what is referred to as the "solar cycle." The last solar cycle hit bottom in 2007, as scheduled, then abruptly stayed at very low levels ever since. It has yet to return to expected levels nearly three years into what should be a pronounced upswing of the next cycle. This is by far the single x-factor that has many forecasters wondering what effect this may have in the months and years to come. The last time the Pacific Northwest saw all three of these factors come into play (La Nina, Negative PDO Phase and Solar Minimum) at the same time was the fall and winter of 1955/1956. The result was one of the coldest and snowiest winters in Portland since records began at the airport in 1940.
Bottom Line
The chances for seeing above normal snowfall and colder than normal temperatures, coupled with at least one potent Pacific storm that could bring high winds across the region this coming winter appears at this point to be trending higher than normal, based on these factors. However, there is still plenty of time to refine things, so get out there and enjoy summer while it lasts.
Steve Pierce
Vice President
Oregon Chapter of the American Meteorological Society (AMS)
503-504-2075 (Portland)
e-mail: stevejpierce@comcast.net
web site: http://www.ametsoc.org/chapters/oregon/
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