Warm November, Normal Winter in Store for Illinois?

The NWS Climate Prediction Center released their outlook for November and beyond. The primary consideration for the outlook was the likely return of La Niña in the Pacific Ocean.

La Niña

In a recent blog post on climate.gov, Emily Becker writes

… now forecasters think there’s a 70% chance that La Niña conditions will develop this fall. However, any La Niña that develops is likely to be weak, and forecasters aren’t quite as confident that La Niña conditions will persist long enough to be considered a full-blown episode, giving it a 55% chance through the winter.

Here is the typical winter pattern for La Nina, as shown on climate.gov, with warmer and drier conditions south of Illinois, colder conditions north of Illinois, and wetter conditions with an active storm track right over Illinois. This active weather pattern tends to produce more snow in the Great Lakes region as well.

lanin%cc%83a_winter_flat_updated_620

November

The outlook for November (below, click to enlarge) shows Illinois with an increased chance of warmer than normal conditions across Illinois and much of the US. Areas in Illinois along the Mississippi River are part of a larger area with an increased chance of being drier than average. My confidence in the temperature forecast remains high. I am less confident in the precipitation forecast. Some of their own precipitation forecasts that extend into early November suggest a persistent wet pattern over the next 4 weeks in Illinois.

November-January

The outlook for November through January shows the southern third of Illinois with an increased chance of above-normal temperatures. The rest of Illinois is labeled EC for equal chances of above, below, or near-normal temperatures. All of Illinois is labeled EC on precipitation. Since they consider November in Illinois to have a higher chance of being warmer than normal, most of the uncertainty in this three-month period lies in the outlook for December and January.

December-February (Winter)

Here is the outlook for the core winter months of December through February. These maps most resemble the typical La Nina winter pattern (shown earlier) with an increased chance of above-normal temperatures south of Illinois and below-normal temperatures north of Illinois. Meanwhile, an increased chance of above-normal precipitation is expected in much of eastern and northern Illinois.

This will be a great forecast if La Nina manages to remain intact through this winter. However, with the odds at only 55%, as noted earlier, what happens if La Niña fades out? The Climate Prediction Center also maintains a set of climate models that make projections out to six months. For the past several months, this ensemble of models (below) has indicated that Illinois and almost all of North America have a chance for a warmer than normal winter. The precipitation forecast closely resembles the official precipitation forecast above with wetter conditions in Great Lakes region.

Other thoughts on this winter:

  1. There are other actors in the winter forecast besides La Nina. These include the North Atlantic Oscillation (NAO), other patterns in the Pacific including one called the Madden-Julian Oscillation (MJO), as well as above-normal ocean temperatures in the Atlantic and much of the Pacific Oceans.
  2. The historical trends in Illinois indicate a move towards warmer, wetter winters in recent decades. However, much variability still exists from one winter to the next.
  3. It is important to remember that most winters in Illinois are not 3 months of unrelenting bitter cold and snow. Most often they are mixtures of periods with mild winter weather and more severe conditions. Last winter included a very warm December with little snow, near-normal temperatures and below-normal snow in January, followed by above-normal temperatures and near-normal snow in February.

March-May (Spring)

For the core spring months of March through May, most of Illinois has an increased chance of above-normal temperatures. It’s EC for precipitation in Illinois; however, the northern states in the Midwest have an increased chance of above-normal precipitation.

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