Where’s La Nina?

January 25, 2011

The whining is beginning to pick up.  From two areas:  First, the general public is now beginning to notice that this January is one mild month!   Snowpack is well below average in the Cascades in the last week of January during a moderate-strong La Nina winter.  I don’t think anyone expected that!  And the average weather junkie noticed the issue about two weeks ago when any chance for low elevation snow or cold totally evaporated from forecast maps.  Two weeks later…still nothing is in the forecast through at least the first few days of February (middle of next week). 

So what’s going on?  The big picture is that we’ve seen persistent upper level ridging near or over the west coast of North America most of this month, and that won’t change in at least the next 7 days.  A deep and cold trough is situated over SE Canada, bringing wave after wave of cold and snow to the eastern 1/3 of the USA at the same time.  Most of the population of the USA is east of the Mississippi River, so we hear a lot more about that.  Not much attention has been given to our mild weather, or the extremely mild weather in most of northern/eastern Canada.  Check out the surface temperature departure from normal over the last 14 days…well above average in the western USA.

I should point out that I was NOT one of those forecasting a “mother of all winters”.  In fact that’s the 2nd or 3rd time in the last 5-6 years I’ve heard certain people forecast that as early as August-September.  Talk about wishcasting…  But I was definitely one of those that believed we had a better than average chance for snow/cold/action this winter.  And there is still time for that.  The last 3 weeks of February COULD still be crazy; we don’t know that yet of course.  But it COULD happen.  Winter is definitely not cancelled yet.  Now if nothing has changed two weeks from now, then that statement would be perfectly reasonable.  We don’t get prolonged arctic blasts or days-long snowstorms with highs below freezing after about Valentines Day.  The increasing sun angle starts to take it’s toll on marginal snow/ice climates like ours by that time.  So I would argue that REAL winter in the lowlands of western Oregon and Washington is over after about mid-February.  That’s only 3 weeks away.

The more important question is why have we have such a strong ridge over us for so long in the middle of winter and why the atmosphere seems to be so locked up?  I haven’t heard a good reason yet.  Cliff Mass talks about it on his excellent blog today here.  And I read an interesting article in the New York Times today that had a few theories.  Maybe the most important point to take from that article was that climate scientists and meteorologists can only guess for now.

So how can this possibly happen during a moderate-strong La Nina?  It’s very rare, but it has happened before.  1999-2000 was a very tame winter, 2nd year of a 2 year long La Nina.  Snowfall that winter was below average in the mountains, although the heaviest snow WAS in January.  Otherwise I don’t see any other January as pitiful as this one during a moderate-strong La Nina winter.  A bit unprecedented.

For the skiers and snowboarders, the good news is that snowfall in the mountains during La Nina winters tends to be best in February and March, so there’s still plenty of time for things to turn around.

Chief Meteorologist Mark Nelsen