Climate prediction is a combination of looking at patterns that historically have affected our region in the past (analogies with previous events) and what computer models are saying about what we can expect this year based on large-scale weather patterns and how they are expected to evolve over time using mathematical formulas and current observations. Since weather patterns are constantly changing, each season will have a unique set of starting conditions that will affect what happens in the coming months. That is why climate predictions are always given as probabilities, because even with the best starting observations and great computer models, they can’t possibly capture all of the variability that is occurring in our climate, and not all possible climate patterns have occurred in the past so analogs don’t always work, especially when temperatures are rising over time.
This year we have a better chance than usual of making a good prediction because winter climate in the Southeast is closely tied to the ENSO phase that is occurring. In an El Nino like the one that is occurring now and will likely last well into spring, we know from past events that we are likely to have a winter that is wetter than average as well as cooler than average due to the presence of a strong jet stream aloft over southern AL and GA and northern FL that will direct storms over that region, bringing cloudy conditions and a lot of precipitation to the area along the path of the jet stream. Because the jet stream position changes somewhat in each El Nino, the actual rainfall and temperature patterns vary from one event to the next. This year’s event has a very high probability of being a strong one based on the current ocean temperatures in the Eastern Pacific Ocean, so that knowledge has factored into the predictions for this winter.
For those of you who like to compare past events to see what patterns show up in common, you can see the most recent precipitation analogs of El Nino winters at https://ggweather.com/enso2023/us_elnino_precip.html collected by Jan Null. If we stick to the ones that are in strong or very strong El Nino winters, we see that in four out of five analog years, winter precipitation is quite a bit higher than normal in our region. That gives us confidence that it is likely (80%) we will experience a wet winter, especially if you are in the area of southern AL and GA and northern FL where the pattern is the strongest. If you are in the Carolinas, then what you are likely to get depends on how strong the El Nino becomes, which we cannot determine yet. But keep in mind that there is still a 20% chance of getting dry conditions instead, so even though it is likely, it is not certain.
For those of you who like to look at all the model predictions, you can see this year’s models at https://medium.com/@melhuish/computer-models-on-this-winter-59da5cc501c3 collected by Kirk Mellish. The different models show a lot of agreement on precipitation, with nearly every model showing a wet winter in southern AL and GA and northern FL. There is less agreement on temperature, with some showing near normal temperatures and a few showing warmer than normal conditions. Since the El Nino tendency towards cooler temperatures is fighting against the trend towards warmer winters due to global warming, the models have a wider variety of predictions about temperature, so that means we are less sure about what the temperature will be like this winter. Analogs don’t help here much either because we have never been in this warming climate pattern before, so whatever happened before may or may not happen this year.
Based on all of these different sources of information, the Climate Prediction Center put out their December through February forecast below. Note that while the temperature in the northern US has a high chance of above normal conditions (El Nino and rising temperatures both indicate a warm winter), in the South we have equal chances of near, above, or below normal temperature because the El Nino impact is opposite the impact of rising temperatures. The precipitation prediction shows the expected wetter than normal conditions across a large swath of the Southeast with the highest likelihood in southern AL and GA and Florida as well as along the East Coast since it is expected to be a strong to very strong event. Now you know why!