"The Boy's" Winter...or Is Winter Over Already?!?!?!

Chris paid me boatloads of money to write a post about El Nino Southern Osciallation (ENSO) and its effects on our region this winter. Disclaimer: I am not an expert on climate cycles...I don't pretend to be...It just makes me feel smart when I use terms like "shear" and "amplitude" and...um..."weather".

Alright...I'll leave it up to the viewing audience to do your homework and google the basics of ENSO (BOTH cool-phase and warm-phase), Pacific Decadal Osciallation (PDO), and Madden-Julian Oscillation (MJO). They all play a role in how ENSO can affect our winters. Then there are the details of ocean circulation patterns, but let's keep it simple.

So getting down to it...ENSO will stick around through at least the spring of 2010 according to the Climate Prediction Center(CPC) at NOAA. Most models are predicting that ENSO has peaked in the December-January-February span and is on the decline with half the models suggesting it will persist through April-May-June 2010. This is all info that can be found on the CPC website from above. So break out the flip-flops, start kayaking tomorrow, and quite a few folks have already started running and riding. It is possible that it will extend into the summer as well. If you want to know a bit more keep reading. If not, have fun sunning yourself the rest of the winter. The CPC provides a nice weekly update (and thorough overall explanation of things like various ENSO indices and updates the 3-month probability graphs at that time):

http://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/index.shtml.

So, ENSO is a result of sea surface temperature (SST) change in the Pacific Ocean due to either a weak or strong upwelling of cold water, and this year is a warm-phase (El Nino). Whereas a cool-phase like 2007-08 is referred to as a La Nina. During a warm phase cycle, the jet stream moves south and becomes more zonal (straight west to east) thus favoring California and the southwestern U.S. The polar jet sinks south and effects eastern Canada and U.S. Whereas in a La Nina year, the jet stream shifts north. This all occurs because of changes in atmospheric heating resulting from changes in SSTs and convection patterns.

This image shows the aforementioned jet stream patterns and as you can see we stay warm and fairly dry.

However, PDO is a climate cycle that shifts every 20 or 30 years and is detected by sea surface temperatures in the Pacific. It manifests itself in ways similar to ENSO, but persists for a much longer time scale. To learn more, here is a link that briefly describes the pattern and provides many more links. http://jisao.washington.edu/pdo/

PDO affects our region in various ways as well depending upon the cool or warm phase. I "borrowed" a few graphs I saw on a skiing forum a while back that I had saved because they depict the situation very clearly. For credit sake, they were created by an individual named "walrus", a weather/climate forecaster in Missoula. If he is reading this, it's Chris' fault.

This one shows how PDO (both warm and cool phases) can affect moderate ENSO winters (+0.5-1.0 degree Celsius) in Missoula.

This graph shows snowfall amounts in the region during moderate El Nino years. The Oceanic Nino Index (ONI) is currently +1.8 degrees Celsius, which is a bit more than moderate. This number is a 3-month running average of SSTs in a certain region of the Pacific that affects us the most in western N. America. However, these graphs are pretty neat.

So, sure, we may still see a nice storm or two in our area this winter/spring, but I wouldn't expect the skies to burst and bring us a "sickter, epic, blower all over, brobra" rest of the winter. We are hovering just around 76% of average (35 year average) for the Flathead River Basin in terms of precipitation and around 72% for snow water equivalence (SWE). Of course, this is only an average for the basin, and some SNOTEL sites are a bit closer to average.

Wow...too much...are you still reading? Go skiing!!!