June – Warmer and Wetter in Illinois, More to Follow

Summary: The statewide average temperature for June so far is 75.3 degrees, 4.4 degrees above normal. The statewide average precipitation for June is 3.61 inches, which is about 130% above normal. However, the precipitation is spread unevenly throughout the state. Above-normal temperatures are expected to continue for July.

Temperature: Both the average high and average low for June has been above normal (maps below). The average high ranged from the low 90s around St. Louis to the upper 80s in the southern two-thirds of Illinois. The average high ranged from the upper 70s to the low 80s in the northern third of the state. The average lows ranged from the upper 50s in northeast Illinois to the 60s for the rest of the state.

Precipitation: Precipitation was highly variable across Illinois, which is fairly typical for summer months (below). There are a few areas in pink with 10 to 15 inches. Areas in shades of orange and red have precipitation amounts of 4 to 10 inches, well above normal. The largest monthly total so far is Beecher City (Effingham County) with 11.22 inches. Meanwhile, rainfall has been less plentiful in western and southern Illinois with amounts of 2 inches or less.

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Outlook: More rain is expected across Illinois the next 7 days as a slow-moving low-pressure system moves across the region. The potential amounts range from nearly 3 inches in northern Illinois to about an inch in southern Illinois.

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The outlook for July from the NWS says that we can expect an increased risk of above normal temperatures for July (top row of the figure). There is no indication of increased risks of either above or below-normal precipitation for July. For the period of July through September (bottom row), the southern two-thirds of Illinois has an increased chance of warmer than normal conditions. The northern third does not. There are no climate factors to indicate an increased chance of either above or below-normal precipitation during the period of July through September.

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Warmest May on Record for Illinois

Temperatures: Based on preliminary data, the statewide average temperature for May in Illinois was 70.6 degrees, 7.9 degrees above normal and the warmest May on record. The old record was 69.4 degrees set back in 1962. A brief examination of daily records indicates that Springfield, Champaign, Quincy, and Carbondale all had daily mean temperatures at or above normal for each day of the month. On the other hand, Chicago, Rockford, and Peoria had a few dips into the below-normal territory but overall finished above-normal for the month. Here is the graph of daily mean temperature departures from normal for Champaign-Urbana.

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“Normal” refers to the standard 1981-2010 average. For daily normals, additional smoothing is done since even a 30-year average can have some variability from one day to the next.

It was not just warm in Illinois. Here are the temperature departures from normal across the US for the month of May.

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Precipitation: Based on preliminary data, the statewide average precipitation for Illinois in May was 3.98 inches, 0.62 inches below normal. Here are the monthly totals and departures from normal maps for Illinois. Click to enlarge. Areas in northern and southwestern Illinois received sizable rainfall amounts. Meanwhile, a few spots in east-central and southeastern Illinois were well below normal, and a cause for concern as we move into the summer months. The highest monthly total reported in the state was at Barrington (Cook County) with 12.69 inches. On the other hand, Effingham reported one of the lower totals in the state with 1.11 inches.

One of the key rainfall producing systems in Illinois in May was when the remains of Subtropical Storm Alberto tracked up the IL-IN  border. As noted in a previous post, the remains of tropical storms have reached Illinois in the past.

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Forecast: The National Weather Service’s Climate Prediction Center released their updated outlook for June. For Illinois, we have a greater chance of seeing the above-normal temperatures continue in June. The area around Chicago has an increased chance of below-normal rainfall, which may be welcome after the wet May. The 6-10 and 8-14 days forecasts are showing Illinois with an increased chance of both warmer and drier than normal conditions for the first half of June.