Wetter conditions across the state of Indiana are favored for the meteorological winter months of December, January and February. Temperature projections are uncertain from the national climate Prediction Center. The La Nina phase of the El Nino-Southern Oscillation factors heavily into this forecast, while the Arctic Oscillation plays a big potential spoiler.
Will Indiana have a white Christmas?
The one-month outlook for December 2022 gives equal chances for above or below normal temperatures and precipitation. Late last year, the National Oceanic and Atmospheric Administration updated the Christmas Snowfall Climatology map, using 1991-2020 data to determine the odds that at least one inch of snow will be on the ground on December 25. Evansville has an eight percent chance of such an occurrence, while Indianapolis has a 26 percent chance. The highest probability in the state is 49 percent in Kingsbury of LaPorte County.
La Nina and the Artic Oscillation
A significant amount of the state lies in dry conditions or drought as of this writing. The extent to which Indiana may retreat from drought status is uncertain. Traditionally, La Nina winters like the one upcoming tend to provide a warm, wet signature over Indiana. However, the temperature signal is stronger in the Southeastern United States and the tendency for warmer temperatures fades before reaching Indiana. Precipitation carries an anomaly for the season of over half an inch above normal for all but the northwest corner of the state. This above-normal precipitation is likely to occur in the latter half of the winter “season” rather than evenly throughout.
Dealing with a traditional La Nina for the third year in a row may assist in removing dry conditions from the state, but the Arctic Oscillation could cancel out the trend as it did in our first of the last three winters. The Artic Oscillation switches from positive to neutral or negative in a matter of weeks, bringing short-term variations in temperatures. A negative Arctic Oscillation is also commonly associated with the term “polar vortex.” Because the Arctic Oscillation is a short-term phenomenon, it is rarely considered when seasonal outlooks are made. The last winters with strongly negative Arctic Oscillations were 2010 and 2014.
Although the amount of uncertainty is higher in the outlook than for some previous years, the likelihood that we leave La Nina behind after the winter season does exist. However, the confidence for this is only moderate at the moment. Persistence would begin to test records for longest-lasting La Nina. In either event, La Nina signatures outside of winter months are less able to influence seasonal predictions.