Heat, Frost, Snow, and Rain – Just a Typical October in Illinois

I love the weather in Illinois – hardly ever a dull moment.  This October we experienced days in the 90s, the first fall frost, the first snow of the season, and widespread heavy rains.

The statewide average temperature departure for the first 9 days of October was 11.5 degrees above normal.  There were many reports of temperatures in the 90s during this period, including a high of 94 degrees in Fairfield on October 7.

After the passage of a strong cold front, temperatures dropped and remained much cooler for the rest of the month.  The temperature departure from October 10-31 was 5.7 degrees below normal.   The warm and cold periods balanced out, leaving the statewide average temperature for October at 54.0 degrees, 0.4 degrees below normal.

Freezing temperatures arrived across most of Illinois on October 21st.  The lowest reported reading was 19 degrees at locations near Stockton, Shabbona, and Champaign.  Historically, the average dates for the first fall frost are in October across the state.

The first snow of the season fell on October 12th.  I happened to be driving through it between Kankakee and Champaign (photo below).  There were widespread reports of traces of snow, meaning it melted as it fell. A few areas reported a small amount of accumulation, including Moline and Bloomington with 0.2 inches.  We do not always see snowfall in October in Illinois, but it does show up in the records from time to time.  However, it is not a reliable indicator of the upcoming winter. IMG_2548

Precipitation was widespread across Illinois in October.  The statewide average was 3.81 inches, 0.57 inches above normal.  Amounts of 4 to 7 inches or more were common in the northern half of the state, which is well above normal. Meanwhile, most of the southern half of the state was drier with amounts in the 2 to 4-inch range, which is much closer to normal for October. The largest monthly total was 8.07 inches in Nauvoo (Hancock County).

Another interesting feature of 2018 so far in Illinois has been the impressive precipitation totals in northern Illinois.  Several stations have received over 50 inches of precipitation through October 31, including Elizabeth (Jo Daviess County) with 54.45 inches. That is 22.66 inches above normal! The maps below show the extent of the amounts over 50 inches scattered across the state (darker red), while a relatively drier band stretches from St. Louis to Chicago.



NOAA Outlook for Winter in Illinois

Today, NOAA released the official outlook for winter (December-February).  Not much to report for Illinois.  The northern third of the state has a slightly increased chance of a warmer than normal winter.  And northeastern Illinois has a slightly increased chance of a drier than normal winter. However, the increased odds are very weak and we are on the margins for those areas.  Historically, the core areas with higher odds on the NOAA maps (for example, the Northwest for temperatures) are more like to be proven correct.

Otherwise, the chances are even-Steven across Illinois for the three categories of above, below, and near-average winter temperatures and precipitation.  Maps below.

One of the most important factors for this winter will be the presence and strength of a possible El Niño event. Currently, there is a 70 to 75 percent chance that El Niño will arrive sometime this fall or winter.  El Niño occurs over the central and eastern Pacific Ocean and involves changes in the atmosphere and ocean circulation.  This, in turn, can affect our winter weather in the US.

Right now the official forecast indicates a weak El Niño, hence the anemic odds over Illinois.  If it had been stronger, the odds of a warmer-than-normal winter would be higher for us.  A weaker El Niño event could mean that other factors have a chance to play a bigger role in our winter weather. However, things like the Arctic Oscillation and the related Polar Vortex are much harder to predict more than a few days in advance.



Above-Normal Temperatures and Rainfall for September in Illinois

Based on preliminary data, Illinois experienced above-normal temperatures and rainfall for September in Illinois.  Here are the statistics for the state:

  • The statewide average temperatures for September was 70.0 degrees, 3.8 degrees above normal and the 12th warmest September on record.  We were on track to one of the warmest Septembers on record until the last cold snap.
  • The statewide average rainfall for September was 4.97″, 1.74″ above normal and the 19th wettest September on record.
  • The hottest temperature recorded for September was 99 degrees at Springfield Airport on September 5.
  • The coldest temperature recorded for September was 30 degrees at Ottawa on September 29.
  • The highest monthly rainfall total for September was 12.43″ at Clay City (just south of Effingham).


Here are the rainfall totals (left) and departures from normal (right) for September in Illinois (click to enlarge).  Rainfall was heaviest in southern Illinois with amounts up to 12 inches and in northwestern and western Illinois with amounts up to 10 inches – all well above normal.  There was a band of drier conditions stretching from St. Louis to Chicago where rainfall totals of 1 to 3 inches were common.

In addition, heavy rains fell across the upper Midwest in September (maps below, click to enlarge).  The rains were especially heavy in Wisconsin, Iowa, and Minnesota, leading to river flooding in Illinois along the Mississippi and rivers coming out of Wisconsin


Temperatures across the Midwest were much above normal in September (map below with pumpkin spice-colored shading – appropriate for this time of year).  While Illinois was 3.8 degrees above normal, Indiana was 4.5 degrees above normal, Kentucky was 5.0 degrees above normal, and Ohio was 5.5 degrees above normal.  The other states were 1 to 3 degrees above normal for the month.


Outlook for October

Finally, here is the outlook for October that was released by the NWS on September 30.  These rely heavily on the more reliable forecasts out to 14 days.  Those forecasts show Illinois with very strong chances for above-normal temperatures and rainfall. As a result, the October outlook also shows most of Illinois with an increased chance of above-normal temperatures and all of Illinois with an increased chance of above-normal temperatures.

On a side note, the 4-corners region (UT, CO, AZ, and NM) are in a severe drought and the expected rainfall will be welcomed there.  The same cannot be said for the Upper Midwest, which was already very wet in September.

See the page on normals for more on this topic.


Hot September So Far, But Relief Is in Sight

Illinois and the Midwest have been running hot so far in September.  The statewide average temperature for September 1-19, 2018, in Illinois was 73.5 degrees and 4.7 degrees above normal.


Days at or above 90 degrees have been quite common this September, especially in central and southern Illinois where we saw 8 to 12 days with temperatures at or above that threshold. Runs of hot weather like this in September are unusual but not necessarily record-breaking. For example, here in Champaign, we have reached the 90-degree threshold 10 times this month (including today).  That’s the 4th highest count for September since 1888.  The highest number of days was 15 set in 1897.



But this is about to change on Friday as a cold front sweeps across the state.  Here is the forecast map for Friday morning with rain ahead of the front and cooler temperatures behind the front.  The NWS forecasts out to 14 days show that colder-than-normal temperatures will prevail with highs in the 60s and 70s and lows in the 40s and 50s across much of Illinois.


From a harvest standpoint, the rains over the next five days may impact harvest with the heavier amounts expected in southern Illinois with potential amounts of 1 to 2 inches south of Interstate 70.  The expected amounts are much less in central and northern Illinois.  A look at the 6-10 and 8-14 day forecasts suggest that Illinois will continue to be in a wetter pattern with above-normal precipitation and below-normal temperatures.


The NWS also released their latest outlooks today.  For October there is a “blob” of cooler-than-normal conditions centered over Iowa and Missouri and includes western Illinois.  Illinois has “equal chances” or EC on precipitation, meaning there is not an increased chance of either above or below normal precipitation.

For October-December, Illinois has an increased chance of above-normal temperatures. There is not an increased chance of either above or below-normal precipitation.  For the most part, the temperature pattern for October-December is based on climate trends (warming) and the odds favoring the arrival of El Niño this fall and winter.


Wet Start to September Thanks to Gordon

Illinois experienced a wet start to September, thanks in part to Tropical Storm Gordon.  The statewide average rainfall through yesterday morning was 3.55 inches.  That is above the 3.24 normal rainfall for the entire month of September.  The highest month-to-date rainfall total was 10.15 inches and came from Clay City (east of St. Louis).

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Both August and Summer Were Warmer, Wetter Than Normal for Illinois

August: the statewide average temperature for Illinois in August was 74.9 degrees, 1.3 degrees above normal.  The statewide average rainfall was 5.25  inches, 1.66 inches above normal and the 12th wettest August on record.

The warmest daily high temperature was 97 degrees reported at Chicago Botanical Gardens (8/5), Chicago O’Hare (8/4), Jerseyville (8/7), and Pittsfield (8/29).  The coolest reading was 42 degrees reported at Rochelle (8.22).

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Battle of the Winter Forecasts

What the Almanacs Say

Recently, both the Farmer’s and Old Farmer’s Almanacs released their winter forecasts (below) and what they say for Illinois is quite different.  The Farmer’s Almanac predicts a “Biting Cold, Snowy” winter while the Old Farmer’s Almanac predicts a “Warm, wet” winter for Illinois.

The Farmer’s Almanac states that it “bases its amazingly-accurate long-range forecast on a mathematical and astronomical formula developed in 1818”.   We have learned quite a bit about the weather since then.  And the phrase of “biting cold, snowy” can describe a typical morning in January and February.

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