January 24, 2011


I just got back from the first day of the annual meeting of the American Meteorological Society downtown at the Convention Center...an exhausting but exhilarating event. Thousands of meteorologists, hundreds of talks, booths and exhibits from a variety of vendors and groups, and free food...life doesn't get much better than that. The theme of the meeting-- "Communicating Weather and Climate" --is dear to my heart and one I shall talk about further in another blog.

But that is not what I want to talk about here; rather let discuss the extraordinary weather pattern we are experiencing.

I took a look at the latest model runs just now and they are truly extraordinary...they suggest we are locked in an pattern with ridging (high pressure) over the eastern Pacific and west coast, with the east coast locked in cold weather with more "nor'easters" pummeling the coast.

Today a front went thought our area and believe it or not, we won't see any precipitation until Friday at the earliest...and that won't last. Temperatures will reaching into the 50s, and yes, there will be some sun.

Now lets get back to the models. If there are right, we will not have any significant weather for 7-10 days (and yes I know the reliability of the models plummet after 4-5 days). Here are some samples, the upper level (500 mb) maps at 30, 54, and 18o h out in time. Remember these are like topographic maps...they tell you the height of a certain pressure surface (500 mb, mb is a unit of pressure). 500 mb is about half typical surface pressure. Where the pressure surface bulges up with have ridge, and where it dips down we have a trough. The flow at this level is roughly parallel to the height lines, with higher heights to the right.

In these maps you can see ridging in the west and troughing in east. The ridging is associated with mild temperatures over us and the troughing with cold temps to the east.

Now this output is from one model, the National Weather Service Global Forecast System model (the GFS). To get some idea of whether we should believe this, I checked the "gold standard" global model, the ECMWF (run by the European Center for Medium Range Forecasting in Reading). Same thing. Then I checked the U.S. global ensemble forecasting system model which runs a large number of model predictions each starting slightly differently. Same story. Like spaghetti? One form of output from our ensemble runs is a spaghetti diagram in which the heights from each of the ensemble forecasts are plotted on the same chart. Here is it for 144 hr (Saturday at 4 PM). Look at the blue lines...each represents a different forecast...and nearly all show a nice ridge. This is strong hint that the atmosphere wants high pressure over the NE Pacific.

Bottom line: The atmosphere seems to be locked in a very anomalous pattern right now and my profession really can't explain it (and I would not take certain NY Times op-ed pieces about Siberian snow being the cause very seriously). Or other NY time pieces suggesting it is global warming. Whatever is going on seems to be overwhelming the normal La Nina pattern around here and over the rest of the western U.S. Our snowpack is below normal and California is wet....a situation normally associated with El Nino years. My profession has years of productive work ahead to figure all this out.

PS: It was very nice speaking to many of you at Weatherfest, which was a big success--perhaps 3-4 thousand people attended. And also thanks to all of you that have provided donations to my department, either for the fund to support our weather modeling, research, and web pages, or the other that helps our students.


  1. The currently modeled high pressure condition during the last week of January and /or the first week of February is not unusual in my experience (I have lived in Western Washington almost 50 years). Almost every year I can recall there being clear weather during that period. I have always wondered why to it is so common an event.

  2. GFS 384hr totals, several times, has not had green anywhere in WA. Thats a rarity sometimes in July and August.

    The trough over Hudson Bay on your charts in just massive.

  3. This is kinda like going to the doctor because you have all sorts of symptoms, but reversed, all the doctors are here and all the symptoms of inclement weather seem to have vanished.

    I hope they gave you credit for their winter tans.

  4. Dry, relatively warm weather in January? I don't really care WHAT the explanation is... I'll take it!




  6. Thanks, Cliff. Was wondering if we had an early-onset Spring, and all the pitchers and catchers had to report to training camp early.

  7. This has been one of the longest lasting (>10 days) "dirty" ridges that I can remember.And probably another five days to go of more of the same.I see that there`s now a hint of the overall pattern retrograding westward beginning around February 10th. It will take about another week`s worth of consistant model runs before I`ll buy into it,though.

    Well,one good thing about this winter is that it will provide us plenty of discussion topics for future NW Weather Workshops and AMS meetings!

  8. Mr. Mass,
    I'm a relatively new reader of your blog and I am really enjoying it. Thank you!

    And now I'm going to embarrass myself by asking what I am pretty sure is a dumb question: as a fisherman, I tend to pay pretty close attention to the weather and how it affects fishing. Living in Western WA my entire life, I've noticed a pattern of "warm spell in January = snow event in April". It seems like there is no way that a weather pattern in January could affect one in April. But is that possible?

  9. Now what happened to the ridge?? raining showing for Friday on...

  10. Thank you for providing interesting, illustrated forecasts and background weather info.

    Even though I am often at the edge of your maps I still find your blog worthwhile.

  11. Thanks for the helpful info Cliff. As a snow junkie I often find myself scouring the internet looking for more information on how to predict the weather of the PNW. Lately I have been reading about the AO and PNA indexes and how they can affect our weather. As far as I can tell the AO is a measure of the pressure in the arctic, a negative reading equates to a higher pressure and thus more arctic air filtering into lower latitudes. The PNA is a measure of the location of the Jet Stream in the pacific, a positive number relating to a southern jet stream with tropical moisture and a negative number equating to a northerly jet stream with colder moisture. By my math it seems like a PNA- + AO- = good skiing conditions, but as long as the PNA is negative, our storms come in from the north and the precipitation in or mountains would be falling as snow. Is all this info I’ve put together from Wikipedia and weather blogs correct, or have I gone off track?

  12. I suspect this ridge to be moved more westward, models are really indicating that right now as well. That would allow for some cold air to spill into our area.


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