Illinois has an increased chance of being cooler-than-average for August, according to the NWS Climate Prediction Center. The new forecast was released on July 31, 2015.
One of the major drivers in the forecast is that we are currently in an El Niño event. Historically, August temperatures tended to be cooler than average during El Niño events.
This forecast of a cooler August follows on the heels of our cool July. Besides El Niño, in the past the temperature pattern experienced in July has a tendency to carry over into August. That is a hot July tends to carry over to a hot August and a cool July tends to carry over to a cool August.
This is largely the result of soil moisture status. Dry soils in July (i.e., drought) leads to warmer temperatures in both July and August. On the other hand, wet soils in July hold down August temperatures as more solar radiation goes into evaporating and transpiring water back into the atmosphere and less into heating up the atmosphere.
Click to enlarge.
Based on preliminary data, July was both cooler and wetter than average for Illinois.
The statewide average temperature in July was 74.4 degrees, 0.9 degrees below average. That is not nearly as cool as our record-setting July 2014 when the average temperature was only 70.3 degrees (5.0 degrees below average). On the extreme other end, July 2012 was 81.8 degrees (6.5 degrees above average). More on July temperature trends in another post.
July Precipitation. Click to enlarge.
According to the NOAA Storm Prediction Center, Illinois is ranked fourth in the nation for the number of tornado reports in 2015. Here are the top five states:
- Texas with 164 reports
- Kansas with 150 reports
- Oklahoma with 100 reports
- Illinois with 64 reports
- Colorado with 48 reports
April 9, 2015. Click to enlarge.
The most outstanding event for 2015 was the April 9 outbreak that produced 11 tornadoes, including a rare EF-4 tornado. The map on the left shows all the severe weather reports for that day. More on this outbreak can be found here.
The map below is for all the tornado reports across the US in 2015. Many of the Illinois tornadoes occurred in far northern and far southern Illinois this year, while central Illinois has been relatively quiet. Continue reading
Here is the latest radar/raingauge estimated rainfall totals for July across the Midwest through this morning.
Much of the Corn Belt has been extremely wet. Heavy rains amounts of 5 to 10 inches are found across Minnesota, Wisconsin, Missouri, southern Iowa, Illinois, Indiana, Ohio, and Kentucky for July. Even portions of the Plains states received 2 to 5 inches of rain, which is well above their typically dry July.
For Illinois, amounts of 5 to 10 inches are found between East St. Louis, Moline, and eastward, as well as south of Carbondale and parts of northeast Illinois. Most of the rest of the state has received 2 to 5 inches. There are even a few small areas with less than 2 inches of rain in southern Illinois and the northwest corner.
July Rainfall. Click to enlarge. Areas shaded in red and purple have between 5 and 10 inches of rain. Areas in yellow and orange are 2 to 5 inches, and areas in green are less than 2 inches.
Illinois was one of the coolest places to live in 2014, at least in terms of temperature, according to the recent annual report released by the National Centers for Environmental Information (NCEI). In the map below, the areas in blue show areas where the temperatures were much colder than average for the central US and eastern Canada, while the West and Alaska were much warmer than average (areas in red).
Temperature departures from the 1981-2010 average. Blue means colder than average while red means warmer than average. Click to enlarge.
According to the latest figures, the average temperature for Illinois in 2014 was 49.5 degrees, 2.7 degrees below the 1981-2010 average, and the 6th coolest year on record for Illinois.
The forecasts for August and the three-month period of August-October show most of Illinois with an increased chance of being cooler and wetter than average.
A significant El Niño event has developed in the Pacific Ocean and has a 90% chance of remaining throughout 2015 and an 80% chance of remaining until next spring. This is expected to have significant impacts on the weather in the US.
El Niño events occur when the waters in the eastern Pacific along the equator are warmer than usual. This changes the weather patterns over the Pacific and US.
Here is the precipitation across Illinois for past 90 days as a percent of average. Click to enlarge.
After a record-setting June, as well as a wet May beforehand and a wet July so far, we are seeing the agricultural impacts of the wet growing season. Right now, the state-wide July precipitation in Illinois is at 3.1 inches. That is about 50% above the long-term average for this time in the month.
According to the USDA report yesterday, only 96% of the soybean crop in Illinois has been planted.
Meanwhile, the corn and soybeans already in the ground have struggled. For corn, 5% of the crop was rated “very poor” and another 11% rated “poor”. For soybeans, 7% of the crop was rated “very poor” and another 13% rated “poor”.
According to the National Weather Service, the potential for heavy rainfall remains – especially in northern Illinois. Rainfall amounts over the next 7 days could range between 1 to 3 inches in northern Illinois, 0.25 to 1 inch in central Illinois, and 0.25 inches or less in southern Illinois. Local amounts could vary widely from place to place due to the nature of the storms.
Click to enlarge.