The atmosphere is violent: Tornadoes, hurricanes, ice storms, hail, and lightning punctuate periods of calm.
The cause of all weather is the clash of air masses created by the geometry of a spinning sphere revolving around a prodigiously radiating stellar object with its axis at a 23 degree angle to its plane of revolution. Movement of air corrects the seasonal, diurnal, and annual imbalances in temperature that result.
The primary cause of large-scale atmospheric movement is the differential heating between the equator and pole, which sets up a high potential energy state of warm air adjacent to cold. Mother Nature’s method of relieving the constantly building potential energy is to move air around until warm air is on top of cold — a lower potential energy state.
The battlefield for the war of air masses is the entire globe, but some places are more compatible for skirmishes than others. The North American continent is particularly suitable for clashes, as cold air plunges south from Canada while warm air surges north from the Gulf of Mexico.
The result can be a winter like the last one, which was brutal for residents of much of the United States — ask anyone in the quadrilateral bounded by Minnesota, Missouri, the Mid-Atlantic, and Maine. Hostilities even spilled into the Deep South and created havoc at times, including a historic traffic jam in Atlanta.
Physics and The Atmosphere: Theory In A Nutshell
Though fluid dynamics is dealt with physically in a different manner than hard-body physics, it is interesting and instructive to investigate the latter to see just how formidable the former can be.
The three body gravitational problem can be solved in certain cases. Extended to numbers greater than three, the problem also has analytical solutions. But the solutions involve series of terms that converge so slowly that they are useless for any practical purpose.
Now consider trying to apply the laws of physics to quintillions of molecules in the atmosphere: quite a daunting task.
Nevertheless, there was a time when meteorologists were hopeful that they could make long-term accurate forecasts using powerful computers and careful observations to approximate the atmosphere to any desired degree of accuracy. This vision proved to be a mirage.
The Equations That Govern The Behavior Of The Atmosphere
Six equations in six variables describe atmospheric movement. Theoretically it should be possible to solve these equations to determine the state of the atmosphere in the future. Unfortunately the mathematics is beyond the capability of modern — and probably future — techniques.
Approximations to the state of the atmosphere continue to improve with better observations. But there’s a problem when it comes to increasing the accuracy of the forecast, regardless of how much computing power is brought to bear.
The Atmosphere Is Chaotic
Beginning in the 1960s, the work of Edward Lorenz and others cast suspicion on the notion that continued refinement of observations and faster computers could result in continually better forecasts.
What Lorenz found was that any tiny error in the initial observations quickly overwhelmed any forecast so that after a week or so it was useless. Meteorology has been in this bind ever since. Chaos rules the atmosphere, and errors, no matter how tiny, explode to wreck all forecasts beyond a very few days.
So How Do We Dare Even Mention A Seasonal Forecast?
Though computational forecasts have significant value for only a week or so, climatologists can use empirical evidence of trends in the atmosphere to glean some information about the weather months in the future — at least in a qualitative way.
Waves In The Jet Stream
Decades of observation indicate that strong westerly winds blow worldwide at middle levels in the temperate latitudes. Waves are embedded in these westerlies, and in the shadows of these waves, the weather at the surface displays certain patterns. The typical wavelength is on the order of 3,000 miles. So, for example, if there is a dip in the jet stream over California, there tends to be another dip over the east coast.
Jet stream dips in the east-central Pacific and the central US characterized last winter’s weather. Between the dips was a ridge, which became very pronounced — an omega block (named for the shape of the Greek letter Ω). Omega blocks tend to maintain their positions for long periods of time.
The Omega Block — also the cause of a serious drought in California- has now faced its most powerful challenge in more than a year. Storms have broken through the ridge and established a trough where the ridge was, bringing beneficial rain to California. Downstream, warm air is replacing cold in the center of the country.
The El Niño Effect
Though a full-fledged El Niño as defined by NOAA has not been certified, the waters of the equatorial Pacific are now considerably above the long-term average. This tends to create a temperature gradient over the Pacific which leads to a southern branch of the jet stream that sends storms spinning towards the west coast.
Omega Block vs. Jet Stream: The Battle Is Joined
The trends of a southern jet stream over the Pacific pushing storms into California and the omega-blocking high pressure cannot co-exist. One will most likely become dominant for the winter, though they could alternate in ascendance. The weather over the eastern two-thirds of the US will depend critically on the victor in this battle.
Right now, the forces of the omega block have been bloodied, and warm air is marching into much of the continent. But extremely cold air still occupies northern Canada, and should the El Niño falter, the California high (legal now) could return, opening the Yukon highway for the armies from the north to invade the plains, midwest and eastern US once again.
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