This was the 5th warmest November on record for Illinois, based on preliminary data. The statewide average temperature was 47.4 degrees, and 4.9 degrees above normal. Here are the top ten warmest Novembers in Illinois since 1895:
2001 with 49.9°F
1931 with 49.1°F
1909 with 48.8°F
1999 with 48.4°F
2016 with 47.4°F
2009 with 47.2°F
1902 with 46.9°F
1990 with 46.8°F
2015 with 46.6°F
1913 with 46.4°F
It was also the 2nd warmest fall on record for Illinois. The statewide average temperature for fall was 59.4 degrees, 5 degrees above normal. Only the fall of 1931 was warmer at 59.8 degrees. The climatological fall months are September, October, and November.
Summary: The NWS Climate Prediction Center has issued their forecasts for September, September-November (Fall), and December-February (Winter). Illinois has an increased chance of being warmer than normal this fall, and wetter than normal this winter.
According to the Climate Prediction Center, the main factors in the forecast are the recent warming trends and the expected La Niña. While the conditions in the Pacific are in the neutral stage between El Niño and La Niña, there is a 55-60 percent chance of a weak La Niña during fall and winter.
The September forecast (top row) has Illinois and the Midwest with equal chances of being above, below, and near-normal on both temperature and precipitation. I call this a neutral forecast since there are no indications that we will be significantly cooler, warmer, wetter, or drier.
The September-November forecast (bottom row) has Illinois and the US with an increased chance of being warmer than normal. They are neutral on the precipitation forecast.
The average temperature for fall in Illinois (September-November) was 57.4 degrees, 3.0 degrees above average. As a result, it is the 5th warmest fall since 1895, based on preliminary data.
The top five warmest falls in Illinois:
1931 with 59.8 degrees
1963 with 58.0 degrees
1998 with 57.7 degrees
1971 with 57.5 degrees
2015 with 57.4 degrees
Here are the monthly departures of temperature in Illinois through the end of November for 2015. All three fall months were warmer than average. September was 4.6 degrees above average, October was 1.7 degrees above average, and November was 4.5 degrees above average.
Monthly precipitation for 2015 shows the near-average September, the dry October, and the wet November. The 3-month total was 10.44 inches, 0.5 inches above average. Of course, this was overshadowed by the wet spring, especially June. In face, Illinois has already reached 41.79 inches of precipitation in 2015, 1.35 inches above the 12-month average.
Over the weekend, most areas of the state saw their first taste of 32 degrees or colder. Here are the maps from the Midwestern Regional Climate Center showing that the almost the entire state was covered. A few places in the Chicago area may have escaped thanks to the so-called Urban Heat Island (UHI) – lots of warm surfaces like roads, asphalt parking lots, roofs, and waste heat from buildings. For example, O’Hare AP reached 33 degrees. Meanwhile, Mt. Carroll in northwest Illinois reported 20 degrees on October 18. Now that’s cold.
The NWS Climate Prediction Center released their latest outlook for October and beyond. It looks like the warm-than-average weather is expected to continue for the next several months. The primary driver in the forecast is the ongoing El Niño in the Pacific Ocean basin.
Illinois has an increased chance of above-average temperatures for October. There is not much to report on precipitation in Illinois. We are between drier-than-average conditions to our northeast and wetter-than-average conditions to our southwest.
Last week, the NWS Climate Prediction Center released their official forecast for fall and winter. Their forecasters used a variety of tools and as well their own expertise to develop those forecasts. While their forecast for Illinois this winter was interesting, the one for fall was not. They had us with equal chances of above-, below-, and near-average temperature and precipitation.
However, there is one forecast tool that showed some results for Illinois this fall. That tool is called the North American Multi-Model Ensemble (NMME). It consist of several forecast models that are run out to 7 months. The advantages of having multiple model runs are that an average of all results tends to be a better forecast than a single model. Also, the spread in the model results gives you an idea of the uncertainty of the forecast. For example, if all the models showed this winter being warmer-than-average, our confidence in the forecast would be much how than if some models showed it being warmer, some models showing colder, and others showing average conditions.
These results below for fall (SON=September, October, November) are considered experimental and not part of the NWS official forecast. However, they do shed some insight on what the models are “thinking” for fall. The first map show the chances on fall precipitation in three categories (wet, dry, average) using all models. They have Illinois and much of the US with an increased chance of above-average precipitation.
The NWS Climate Prediction Center released their latest seasonal forecasts today. Here are the results for Illinois. The biggest news is that Illinois has an increased chance of above-average temperatures and below-average precipitation for the winter months of December, January, and February. This forecast is based largely on the developing El Niño in the Pacific Ocean.
While the forecast of a milder winter may sound appealing, I would not leave the winter coat in the closet and throw away the snow shovel just yet. Two things to consider are: 1) this is not a 100% guarantee, other factors come into play in determining our winter weather, and 2) even a mild winter can contain short periods of intense cold and abundant snowfall.
If you look at the start to September, temperatures have run 3 degrees above average. And yesterday and today have been the hottest yet with temperatures the 80s and 90s across much of state. But that is about to change as a cold front pushes through later today. This weekend and next week will be cooler with highs in the 70s and low 80s. I am looking forward to that.
Average daily highs in September in Illinois range from the low to mid 70s in northern Illinois to the low 80s in southern Illinois (map below, click to enlarge).
The NOAA Climate Prediction Center released their monthly outlook for September and 3-month outlooks for September and beyond. At this time, they are not expecting a repeat of last winter for Illinois.
According to them, the chance of El Niño has decreased to about 65% during the Northern Hemisphere fall and early winter. If it does show up, it is expected to a moderate to weak event. As a result, the impacts on the US and the Midwest will likely be modest at best.
September and FALL
For both September and this fall, there is an equal chance (EC) of above, below, near-average temperature and precipitation (4-panel figure below) for Illinois. The north-central US is not expected to have below-average temperatures, like it has experienced this summer. This may give crops in those areas a better chance of reaching maturity this fall.
It does look like temperatures are expected to stay above-average on the West and East Coast, as well as Alaska. Wetter-than-average conditions are expected to prevail in the southwest US, and expand into the Plains and parts of Iowa and Missouri later in the fall.
For Illinois, the current forecast is for equal chances of above, below, and near-average temperatures. Or to put it another way, they see no sign of a repeat of last winter. And they are expecting below-average precipitation in Illinois and across the Great Lakes region. It is still early in the year to lock in on this forecast so I would not cancel orders for snow blowers or salt deliveries just yet.
Here are the median dates of the first time we hit 32 degrees in the fall. Since we don’t have reports of when frost occurs, we use 32 degrees as a proxy. It is no surprise that the frost date occurs earlier in northern Illinois than southern Illinois.
If you look closely, you may see differences of several days between neighboring sites. Nighttime temperatures, especially on calm, clear nights in the fall, can be very sensitive to the local conditions. Sites in town tend to be a little warmer than those in the countryside, and result in delaying the arrival of colder temperatures.
Chilly temperatures have already visited the northern part of the state this weekend. Mt. Carroll reported a low of 29 on September 23 and Elizabeth reported a low of 28 on September 24.
You can read more about frost and see many more maps on the state climatologist’s frost webpage.