Thursday, August 22, 2013
People always want to know what the upcoming late autumn and winter weather will be like. Of course, it’s impossible to predict individual storms so far out in advance (but that doesn’t make the Old Farmer’s Almanac any less entertaining), but it is certainly possible to make some general predictions of the type of weather any one place might see. Solar activity cycles and oceanic temperature oscillations are just a few of the characteristics forecasters take into account when making long-term predictions. Of course, if you look in the super long term, forecasts become more based on greenhouse gas concentrations than anything else, but their impact right now is low compared to natural variability (except in the arctic summer). The world will be a completely different place 100 years from now
By far the most notable pattern I’m aware of that affects weather season-to-season is the state of the equatorial waters of the eastern Pacific as a function of El Nino Southern Oscillation (ENSO). There is a general cycle of warm and cool SST in the eastern Pacific, and these phases are called El Nino and La Nina phases, respectively. They both occur every 3-5 years and usually (but not always) oscillate. When the SST in the eastern Pacific are average, we say that the ENSO is in a “Neutral” phase. It looks like we will, just like last year, be in a solid Neutral phase for this upcoming winter.
Occasionally, I do blog “projects” as opposed to blog “posts,” and I did one such project about ENSO back in 2012. I’d recommend giving it a thorough read before the rest of this post so that you can better understand how ENSO works, but I thought I’d just give a brief review of the effects of El Nino, Neutral, and La Nina events over North America.
|El Nino Conditions. Retrieved from the NWS’ Climate Prediction Center website|
When there is a strong El Nino, the Eastern Pacific High, a semi-permanent ridge of high pressure in the Eastern Pacific, gets “less high” (weaker). When it does this, the jet stream off the Pacific shifts south and tends to deliver an endless barrage of storms to California, while the polar jet stream stays well to our north, leaving us in “no man’s land” between the two jet streams and giving us warm and dry weather. That’s right… folks in L.A. get all these massive cyclones while us Pacific Northwesterners are mere spectators. I hate El Nino winters for a variety of reasons… far too many to count. Upwelling along the Pacific Coast is reduced, so the fishing sucks, and skiing generally ranges from adequate to horrible.
|La Nina Conditions. Retrieved from the NWS’ Climate Prediction Center website.|
La Ninas are actually pretty cool. We are generally wetter and cooler than normal, and since upwelling is increased along our coast, salmon get big and healthy. Instead of having one persistent Pacific jet stream to our south and an polar jet way up north, a big ridge of high pressure over the Eastern Pacific acts to split one jet stream into separate Pacific and polar jets; just like a rock in a river pushes water to either side of it. The Pacific jet stream doesn’t usually get super strong, so while we may remain in a wet and cool pattern, we usually don’t get big honkers of storms.
But Neutral… that’s where things start to get interesting.
|Neutral Conditions. Retrieved from the NWS’ Climate Prediction Center website|
Neutral years tend to be highly variable. Sometimes, the Eastern Pacific high will retrograde to the west and allow the polar jet stream to come into our area, giving us cold, snowy conditions. Our last significant arctic outbreak was during the winter of 2008-2009, which was a Neutral winter. Our last major windstorm (the Hanukkah Eve Storm) for Western Washington was in December 2006, which was actually a very weak El Nino year (there was an even bigger one in December 2007 (The Great Coastal Gale), a La Nina year, but this only affected this coast). November 2006 was straight-up insane and was the craziest month that I can ever remember for Seattle weather (rumor has it that the entire 1861-1862 winter was off the hook, though). Sea-Tac got 15.63 inches of rain, crushing the previous January 1953 record of 12.92 inches, and we tacked on some thundersnow at the end of the month. Take a look at the picture below, and you’ll see that there is a very clear correlation between windstorms and Neutral years.
On the other hand, last winter was also a Neutral winter, and I essentially dozed off to sleep.
I have a habit of making mathematical analogies for essentially everything… a skill I no doubt picked up from Mikko Nynas, some weird Scandinavian 70’s transplant guy who thinks we’re friends. I was thinking about the strength of an El Nino/La Nina in terms of temperature departures from average in the Nino 3.4 Region, the main region meteorologists use for forecasting and observing the current state of ENSO, and how this corresponded to the easiness of a seasonal forecast. I ended up graphing the hyperbolic function 1/x to approximate the uncertainty a typical Pacific Northwest forecaster has as a function of SST departure from average in Nino region 3.4.
We just missed the Mukilteo/Clinton ferry by one car.
Anyway, let’s get back to mathematical representations of psychological fortitude as a function of how warm the water is 5,000 miles from here.
I let the x-axis equal the departure from normal of the SST in degrees Celsius, and I let the y-axis correspond to the uncertainty of long-term forecasters in second-guesses per hour. As the temperature anomaly increases, forecasters second-guess themselves less and less per hour. This is actually not desirable, as the forecaster’s brain activity will slow down more and more until they are a neuron away from entering a vegetative state.
The opposite is not desirable either, though. If the anomaly becomes closer and closer to 0, the forecaster will second-guess himself more and more. Soon, he will be second-guessing himself so much that his body will go into overdrive in an attempt to keep up with his ridiculously flippity-floppity mind. His pulse will reach millions and millions of beats per minute, and because his basal metabolic rate will be so high and he will have such a caloric deficit, he will evaporate into air until only an infinitesimally small quark exists.
Will I vegetate, evaporate, or somewhere in between? Let’s take a look at the current SST.
|Tropical Pacific Measured SST and anomalies. Week ending Aug. 14. Retrieved from NOAA CPC (Climate Predoctopm Cemter)|
As you can see, the temperature is close to average in the Eastern Pacific. It looks to be half a degree lower, but this anomaly has been getting smaller, and and in any event, a 0.5 degree anomaly is not large enough classify the current status of the equatorial Pacific to classify an event as a La Nina event.So I think I’ll have a nice, healthy degree of uncertainty… enough to keep me blogging, but not too much that I’ll forget to take joy in all the other aspects of life.
Speaking of forgetting to take joy in all the other aspects of life… I’ve been laboring days and days to try and find what the integrals and derivatives of this function mean for forecasters, but I haven’t been able to find any. If anybody has any ideas on what ln(x) or -1/x2 represent, let me know. That includes you, Mikko.
Finished Monday, August 26, 2013