February 05, 2010

Why was January so warm? A detective story.

As I mentioned in an earlier blog, January 2010 was the warmest on record in Seattle (back to 1891) and one of the warmest years at virtually every western Washington site with long records. This is a major record. The big question is why? What was so extraordinarily unusual last month?

Yes, it was an El Nino January and they tend to be warm...but why should this be the warmest of ALL of them?

Global warming? No way, the East Coast is having a cold year! And in any case, the West Coast is the place where global warming is weakest and most delayed in the U.S. (reason--our proximity to the slow to warm eastern Pacific).

No it is something else...the unusual alignment of several factors the provides the explanation. And the answer also explains why yesterday got to 57 and today 58F!

This is an interesting detective story. We start with a year with general El Nino conditions--one in which cold air is pushed way to our east. But it took something else--in fact two something elses.

Look at the temperature and precipitation records below you notice a few things. First, the temperatures often were higher than than the average maximum, and we NEVER dropped to the average minimum. The first half of the month was fairly warm and very wet. Clouds held in, preventing infrared nighttime cooling. Southwesterly flow brought in warm air (yes, sometimes we had pineapple express conditions). Hawaii came to you.

But then we dried out and then the temperatures got even WARMER. And is was this spike to April temperatures between January 15-21th that really threw us over. It was also during this time that low pressure records were set over much of the west. The jet stream was way south of us...over CA and northern Mexico. Normally, we are cold when the jet is that far south. What could have done it?

Red is temperature, light red straight line is average max, blue min

Red is cumulative precipitation, blue is climatological average precipitation.

The answer is revealed in the next two weather charts. They are both for 4 PM on January 17th (0000 GMT January 18). The first is for a level about 5000 ft above the surface (850 mb) and the second shows sea level pressure at the same time. The pattern they show was very persistent during period of the warmest temperature. You will notice a low to the southwest of Washington and strongest flow going into California. Wind flows roughly parallel to the solid lines, with southwesterly flow going into CA and southern Oregon, and southeasterly flow over us.

That was the secret! Warm air was moving into off the ocean, circling around to our south and east and then moving into western WA from the SE. As the air descended the Cascades, the air further warmed by compression. If the low had shifted south or north we wouldn't have the perfect combination of southerly flow that sank over us and warmed us further.

And as long as we are talking about heat, January 2010 was one of the warmest on record worldwide based on satellite sensors. Check out the figure:

Why so warm? A major factor is the moderate El Nino we are in. Plus, the earth is relatively warm from the global warming of the past several decades.

And another major item: the sunspots are back on the sun. There are now 22 of them. There was a lot of concern when sunspots didn't return on schedule, but belatedly the sunspot cycle has started.


  1. Hi Cliff,

    sorry i comment so much but you always mention stuff i'd like to explain.

    I visited my Grandpa today and he asked why its been raining so much. Well I said El Nino, warmer and drier than normal. Warmer yes.

    But rain wise, not extrodinary, for how weak diffluent in this el nino split the storms have been, we have picked up 4.5in since christmas day, half our annual. We swapped sides with you. Yakima airport is a drier hole like Seattle, but a few miles west, we are like North Bend in that persistant SE flow. Its been raining when the radar doesn't even show anything, which is usually the opposite. We have only seen the sun twice since Christmas, we are all depressed.

    There are two ways we get cold here east of the mountains. Cold flow N from Canada or radiational cooling from the long nights. Well the upper SW flow you mention cancels out number 1, and the persistant moist boundrary layer cancels out number 2.

    How does that contribute to Seattles warmth? A lot of times in January when air bleeds through the mountain gaps, its 10 - 20 F through the passes, but this month with it warm on the eastside too, it was 30 - 40 F. Add the compressional componant you talked about and it made it 50+ in Seattle which added to an extrodinary warm spell.

    This winter has been boring though. I noticed extended models maybe show a more consolidated flow end of next week. I only hope.

  2. Cliff, I am a regular, but relatively "un-technical" reader. A primer on Sunspots would be appreciated.

  3. Cliff,
    I just want to thank you for your wonderful blog. I'm a casual weather observer, and I ALWAYS learn something from your posts. Thanks for the time and effort that you donate to the cause. It's much appreciated!

  4. cliff; would you consider setting up a facebook fan page for your blog? it can be set to automatically populate your new posts into a subscriber's news feed. I love your appearances on NPR and PBS but sometimes forget to keep track of your blog... just an idea I hope you might consider. thanks for all the work you do! -Phillip

  5. Solar variability (sunspots) have a climate forcing lag on the order of 1-2 years, however, and TSI is still nearly at solar minimum levels. The sunspots didn't have anything to do with our warm January.

    Another thing to note about the global climate is that even though it was cold in the Eastern US, we still set a global record for January satellite temperature (and probably in HadCRUT, GISS, etc when those numbers come out). Just because cold arctic air spills into the CONUS, that doesn't mean the whole globe got cold...

  6. Okay, a dumb question -

    Why would anyone be 'concerned' about the lack of sunspots?

  7. If we had to pick a month for record highs - I'll always vote for January. Much better than that 104f we had last summer. Great job on the explanation Dr Mass!

  8. Cliff, thanks for all the great info on El Nino. A question: We usually talk about El Nino's winter effects. What should we expect for the coming Summer? I'm also a Gorge windsurfer, so would be interested in your thoughts on what to expect for Gorge Summer winds with El Nino in effect.

  9. "Global warming? No way, the East Coast is having a cold year!" ...ok, but haven't you've taught us all to not use localized weather to define climate?

    "...as long as we are talking about heat, January 2010 was one of the warmest on record worldwide... A major factor is the moderate El Nino we are in. Plus, the earth is relatively warm from the global warming of the past several decades."

    I'm having trouble reconciling those statements and wonder over the complex interactions generated by adding a step function (in geological time scales) of heat to the earth's systems. Don't we risk erroneous assumptions if we count on weather patterns remaining static?

  10. @Phillip Jeffries - There is a Facebook fan page out there for the Professor. I went ahead and linked it back to this blog...

  11. excellent report. keep up the great work. I had visited another weather blog and they mentioned it was snowing in CA at the Olympics today when it was clearly rain!



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