WeatherWatcher: La Nina advisory - what does it mean locally?

Thursday, September 22, 2011

On September 8th, 2011, the National Weather Service, Climate Prediction Center released their latest El Nino/Southern Oscillation Diagnostic discussion.

A La Nina advisory has been issued. La Nina conditions have returned in August and may get stronger as we approach and continue through the winter of 2011-2012. The strength of this winter's La Nina is still in the air right now, however typically they are weaker than the previous year in a "double dip" La Nina.

What I call a double dip La Nina (La Nina 2 years in a row) has not been very common over the past four decades. However remember the prolonged snow event we had in December 2008 lasting several weeks? That was also a double dip La Nina winter.

What this means for Shoreline and Lake Forest Park

Fall: 
Effects of this weather pattern are not expected to strengthen until late fall, about Mid-November on. For the rest of September and October we are expected to have slightly above normal average temperatures, with above average precipitation, or in this case, rain. There are concerns we could see more urban flooding than normal, local creeks may have more erosion, especially in Lake Forest Park.

Winter: 
We will have continued above average precipitation, with colder than normal average temperatures returning around Mid-late November, not unlike last winter. La Nina winter conditions favor more frequent, or more intense snow events than normal in the area, however there have been past La Nina winters with little or no snow fall. Due to other oceanic currents and ocean surface and sub surface temperatures globally it is possible that we may have one of the worst winters we've seen in decades.
I will wait until we get through the first half of November before we talk about what spring may be like. It's better to prepare for a few snow days, and severe weather now, than to wait until forecasters start talking about specific storms, that's when everyone else will dash to the store for supplies. So get ready now, and save your self some stress, for possibly another winter like 2008-2009, and last winter. Remember September is National Preparedness Month!
My judgment on our local weather is based on my past experience studying the effects of ENSO locally and of studying historical weather events that occurred here and in the greater Seattle area since record keeping begin, coordinated with the known past of the ENSO status each year.

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