Month: November 2015

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Average Date of First Snow in Illinois

I have noticed that the average date of the first snow is a popular search term on the blog, so here is the reposting of the median dates of the first measurable snowfall of the season in Illinois. This map is based on 1971-2000 data. While it is not based on the current 1981-2010 averages, the map is still relevant for the purpose of getting an idea of the dates. Measurable snowfall means at least a tenth of an inch.

Median Date:

In the northern third of Illinois, the first snowfall occurred around Thanksgiving. The dates switch from November to December once you reach central Illinois (just north of a line between Quincy and Champaign). By the time you reach Carbondale, the date can be as late as December 20. From this you can see that we are by no means behind schedule this year.

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Early Date:

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November Warmer Than Past El Nino Events

While we have one of the strongest El Niño events occurring in the Pacific Ocean basin right now, the effect on November temperatures is typically quite chilly. Looking at the past 5 strong El Niño events since 1950, November was colder-than-average in three events (1972, 1982, and 1997), average in one event (1957), and warmer-than average in one event (1965).

Here is how this year stacks up to the monthly temperature departures from the 1982-83 and 1997-98 events. As you can see (circled), November 1982 was slightly below average (-0.4 degrees) while November 1997 was well below average (-3.9 degrees). This November so far is 5.9 degrees above average.

In the last two big events, the above-average temperatures did not appear until December, January, and February. So what does it mean if this November is unlike 1982 and 1997? It just means that no two El Niño events behave in exactly the same way.

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Click to enlarge.

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Widespread Heavy Rain Expected this Week

The rain has finally moved into Illinois this morning. According to the National Weather Service, widespread heavy rain is expected to continue in Illinois over the next 3 days. Here is the forecast map for Tuesday morning showing a large storm moving across the central US. Rain is likely from the Gulf of Mexico all the way up to the western Great Lakes. Snow is likely in the Plains states (areas in blue). However, we will likely be too warm in Illinois to see snowfall.

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Forecast map for Tuesday morning. Dark green means that rain is likely. The blues back in Colorado, Kansas, and Nebraska means snows. Source: NWS.

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Soil Temperatures in Illinois, Waiting for the Drop Below 50 Degrees

One of the impacts of the warmer-than-average weather in October and November is that soil temperatures have been slow to fall below 50 degrees . This is the important temperature threshold for those applying fall fertilizer (55 degrees with an inhibitor).

You can track daily soil temperatures from the Illinois Climate Network site:  http://www.isws.illinois.edu/warm/soil/ 

As of this writing (November 13), yesterday’s daily high soil temperatures at 4 inches were still ranging from 49 degrees in the north to 58 degrees in the south. Naturally, the air temperatures are going to have to get into the 40s and stay there for these soil temperatures to continue to drop. However, the NWS forecast for the coming week shows highs in the mid to upper 50s in the north and in the low 60s in the south.

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