Here are some Halloween statistics for locations across Illinois. Typical for Illinois, Halloween can be either near freezing or downright balmy. This year’s Halloween will likely be warmer than normal with highs ranging from the low 60s in northeastern IL to the upper 70s in southern IL (map below), but not record breaking. Last year was much cooler with highs in the 50s and low 60s, and a band of rain from St. Louis to parts of Chicago.
Based on historical data for Illinois, the weather in November is trending towards warmer and wetter conditions over time. Based on the latest NWS forecasts, this November is likely to continue that pattern.
The statewide average temperature for November shows a wide variation from year to year – typical of all months in Illinois. However, there is an underlying warming trend of about 2 degrees over the last century.
[Edited on October 26 to reflect update] Based on data through October 25, the statewide average temperature for Illinois in October is 60.7 degrees. That is 6.3 degrees above normal and the fourth warmest October on record. Temperatures for the rest of October are expected to be 3 to 5 degrees above normal. Therefore, this October could slip in the polls. Here are the top ten warmest Octobers
1963 with 63.6°F
1947 with 62.2°F
1971 with 61.3°F
2016 with 60.7°F
1900 with 60.6°F
1956 with 60.2°F
2007 with 59.9°F
1897 with 59.7°F
1950 with 59.3°F
1920 with 59.2°F
Here are the U.S. temperature departures for October so far . Illinois and the eastern two-thirds of the U.S. are experiencing above-normal temperatures (shown in various shades of pumpkin spice, appropriately enough). Speaking of pumpkins, the harvest for this year looks much better than last year.
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.
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.
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.