They're probably the most tossed around weather terms that few know anything about: El Nino and its sister event La Nina.
El Nino is a warming of the ocean waters in the Equatorial Pacific Ocean. La Nina is the opposite -- a cooling of the waters in that region. It's also known overall as "ENSO" -- short for "El Nino- Southern Oscillation" and it changes about every 1-2 years with a complete cycle going about every 3-7 years.
Scientists are still not quite sure what causes it, but these events have a wide-ranging effect on the global climate as it affects the trade winds in the area, which then have compounding effects elsewhere -- especially on the jet stream.
There are two jet streams across the Pacific Ocean -- the polar jet, which is the big kahuna and is the main driver of storms across the ocean, and the tropical jet, which is considerably weaker and generally flows across Mexico.
The average position of the polar jet stream points right at the Northwest during the fall and winter, keeping us generally wet and breezy through the period.
With El Nino, the average position of the polar jet in the fall and winter moves north into B.C. and leaves us high and dry with generally warmer temperatures. (These are typically our really dismal ski seasons.)
A secondary effect is that it energizes the usually-weaker tropical jet stream and brings it a bit north along the southern United States. Thus, El Nino typically spells a very wet early winter for southern California with mudslides a frequent calling card and flooding across Texas and the southeast.
On the flip side, La Nina means a cooler winter for the Pacific Northwest, as it draws the polar jet stream farther south and lets us tap into that cooler air to the north. (This can go either way for wetter vs drier than normal, since the north side of the jet tends to be cooler but also weaker for storms). La Nina winters, like this past one, do typically do quite well for mountain snowpack as it tends to keep snow levels lower.
In the middle is the "neutral" year -- when ocean temperatures are at their middle point between El Nino and La Nina. That is where we are right now and where we will likely be this winter.
For neutral winters, the average position of the jet stream is pointed right at us, but that means it's easy for it to drift north or south for a period. Thus, neutral winters are typically a wide variety of weather, marked with extended dry periods, extended wet periods, some windy storms here and there, and perhaps a few warm, flooding "Pineapple Express" storms and a few good snow events tossed in for good measure. In other words, expect everything and all bets are off.
Although not every winter goes to script. The very wild winter of 2006-2007 was a weak El Nino year, which we would expect to be fairly tame but might go down as one of the stormiest winters ever, what with November setting records for monthly rainfall and December having the region's worst windstorm in 15 years, plus the big snow at the end of November.OK, so we've burned some time having you read all that, but the point of the "Weekly Time Waster" is to find some Web sites to spend your lunch hour perusing, so here we go:
This site shows you historically what years have been El Nino (red numbers), La Nina (blue numbers), or neutral (black numbers).
Going here shows the anticipated effects on Washington and Oregon during an El Nino year.
What about La Nina?
This will show impacts region by region of an expected La Nina year.
And here is a map that shows how much snow has fallen in select Northwest cities during each phase:
(Interesting that El Nino would rate ahead of a neutral year in Seattle, but I wonder if there was one winter that skewed the data because I'd think overall, El Nino would be the least, as it is in most other northwest cities.)
Now, ENSO is not the end-all/be-all of climate effects. For one, there is the "Pacific Decadal Oscillation" (PDO) that is also a change in Pacific Ocean temperatures, but it's more gradual and seems to go in 20-40 year periods than the more typical 1-2 year cycles of ENSO. From, 1925-1946 and again from 1977 to the turn of the century, we were in an apparent warm phase. On the other hand, we were in an apparent cool phase between 1890-1924 and again from 1947-1976 (And gee, all those snowstorm records from the mid 50s for Seattle.)
Could we be due to head into another cool phase? Guess we'll see. But it's important to note that you can still have El Nino/La Nina on top of these greater phases. A warm phase might enhance an El Nino period and limit a La Nina period. And vice versa.
And to top it off, there could be even longer cycles out there of something else. Good to know that climatologists won't be bored and have to read these time-wasting blog entries any time soon :)