The heat and drought suffered in much of the country this spring and summer, especially in the middle of the nation has thoughts turning to when it will end. It has already begun to ease, but of course the natural progression of the seasons makes this partially inevitable. Some hot weather is still to come in Georgia but the worst of summer is behind us now and the dog days of summer have ended.
In making long-range outlooks forecasters look at persistence charts, we tell us the degree to which a particular month or seasons weather is likely to continue into the next month or season or likely to reverse. Research tells us that on a national basis the greatest persistence of temperature patterns is June to August and again for December to January. So we know the summer is not a good predictor of fall or winter weather. In other words, from an historic climatological view point the coming two seasons can go either way following a hot summer…because they have in the past.
The lowest correlation of persistence is between October and November, or put another way. October temperature patterns yield almost zero clue as to what November will bring.
We also look to Sea surface temperatures in both the Pacific and the Atlantic Oceans. There tend to be vast pools or swaths of water where the temperature is well above or below average. How much above or below is significant but more so is where these huge swaths are located and how they are co-located with other pools of warm or cold seawater. This is because research has shown that these patterns in the ocean impact the jet stream, which controls much of our weather. The photo here shows JUST ONE of many such ocean-atmosphere relationships.
By way of examples, a cold pool of water Northwest of Hawaii is a signal for a cold air trough in the Eastern half of the U.S. in winter, especially if it is paired with warm water in the Central tropical Pacific Ocean. Another example is that colder than normal weather along the West Coast of North America favors a split-flow in the Jet stream in winter and a trough near the West Coast. This favors a milder U.S. winter especially along the southern tier of states. Warm water along the West Coast on the other hand favors a ridge or +PNA pattern that sends a sharp cold dip in the jet stream over the eastern U.S. When the Atlantic Ocean has a warm water bias especially with warmest relative North Atlantic and South and a colder pool in-between, known as a tripole, this favors a negative NAO and blocking that delivers cold air East of the MS River.
Of course these things can be measured and observed but they are not static and will change with time. So we attempt to predict how the oceans will be in the seasons ahead in order to try to predict the weather for the seasons ahead. No small task. And this is but one small slice of the numerous factors we investigate to make long-range forecasts. As we assess each we try to find matches to previous years that were similar yielding what are called analogs or analogue years. It’s a matching scheme system. This is the premise that what is past is prologue. Of course they may be similar but no two years are ever the same but may share similarities.
Here is the current list of analog years for the coming autumn and winter. The list will change as ocean and atmospheric parameters change in the months ahead. But for now the list in no particular order is this: 1951, 1953, 1954, 1957, 1935, 1963, 1968, 1991, 1994, 1988, 2002, 2004, 2006, 2009, 1986, 2003, 2007, 1976, 1977, 1911, 1958, 1964, 1969, 1978, 1910, 1970, 1973, 1978, 1987, and 1936.
This list includes all factors including solar, ENSO, Atlantic SSTA, Global AAM, teleconnection indices, summer weather etc., hence some inconsistencies. I hope to separate the analog wheat from the chaff in the months to come.
I previously posted the August outlook and general outlook to October.
As of now the ocean patterns and other data point to the September through November period as a whole having temperatures in Georgia near average (90-day period not every day, week or month). The analogs also suggest that if the entire period does not average near average, then the best chance for temperatures below normal would be October and/or November. The analogs predict the September-November period to have near-normal rainfall in Georgia. For what its worth most of the computer models show a warm and dry autumn season in most of the USA.
For now the analogs predict winter in Georgia will be cooler than normal, with above-average precipitation and above normal odds of snow or ice. Many computer climate models are showing the same thing as the analogs. We shall see if this holds going forward.
Seasonal weather forecasting is still in its infancy; the long track record shows only slight skill. For example, a couple years ago the winter forecast consensus was very much on the money, last year on the other hand was embarrassingly off the mark. This is the way it goes in trying to predict the future, especially the moody ways of Mother Nature.
Anyone know who’s going to win the World Series this year? What two teams will be in the Super Bowl and who will win? How about the stock market next month or next year?
As Yogi Berra said: “The future isn’t what it used to be”.