Before I get into the setup for later this week I want to address a topic that a few folks contacted me about. The Herald had an article briefly discussing La Nina and what that could mean for us.
La Nina is a phenomenon that occurs when the oceans in the equatorial region of the Pacific ocean cool. This is the opposite of an El Nino where the waters in the same region are warmer than average.
The alternative to La Nina and El Nino is when historically average temperatures occur in that region of the Pacific. Over the years the term has changed from neutral conditions to “La Nada”. These phenomena are all part of the El Nino Southern Oscillation (ENSO) Index which along with a number of other factors can affect the weather across the globe.
La Nina and El Nino are classified in 4 ways: Weak, Moderate, Strong, and Very Strong. Technically, you can have El Nino or La Nina conditions without an advisory being issued. After 5 consecutive overlapping 3 month periods with temperature anomalies of +\- .5 degrees an advisory is issued.
A Strong La Nina occurs when the temperature anomalies are -1.5 to -1.9 degrees. Prior to the current Moderate La Nina, we have experienced 3 Strong La Ninas in the last 21 years. 1999-2000, 2007-2008 and 2010-2011.
There are 4 different regions in the equatorial Pacific where warming or cooling occurs. The Nino 1+2 region is closest to South America. The Nino 3 region is the largest and it is west of 1+2 region. Next is the Nino 3.4 region which is the smallest region and it is west of the 3.0 region. The last is the Nino 4 region which extends nearly to Australia and Papua New Guinea. Which region or regions warm or cool affects the amount of influence these phenomena have on our weather.
There are several other influencers on our weather that I am not going to go into but in my experience, ENSO has less influence on its own than some of the others.
Our snowiest winters have historically occurred during ENSO neutral (La Nada) events. 2007-2008 was a Strong La Nina winter but the snowfall was significantly above average. 2010-2011 was also a Strong La Nina and we had below-average snowfall.
When people get excited or concerned about La Nina or El Nino I tell them there are a lot of others factors that influence our weather and not to worry too much about it.
The last 24 hours have brought a little more consensus among the models on the upcoming system. It now appears the first system will track a little closer to the Colorado border and linger a little longer to mingle with the cold system coming down from the north. This would be better news for most of us and would result in our seeing some snow as early as Thursday evening. I am going to hold off one more day to post the current model forecasts but at the moment I am seeing what could be advisory snowfall amounts for Telluride, Ouray and Silverton, and maybe even Wolf Creek.
I hope that answers the questions I got on La Nina. Next Update Wednesday, thanks for following!