First Half of July – Hot and Dry

Rainfall

The statewide average rainfall for Illinois in the first half of July is only 0.8 inches. That is 1.2 inches below average or 40 percent of average. The statewide 1981-2010 average rainfall for the first half of July is 2.0 inches.
The driest July on record was July 1930 with only 1.01 inches. Next in line was 1916 with 1.23 inches and 1936 with 1.24 inches. More recently, 1983 came in 12th place with 1.93 inches and 1988 came in 25th place with 2.60 inches.

Temperature

The statewide average temperature for the first half of July was 82.0 degrees, 6.2 degrees above average. The hottest July on record was 1936 at 83.1 degrees.
Based on preliminary data, there have been 186 new daily records set in July so far and another 33 tied previous records. You can check out the records yourself at http://www.ncdc.noaa.gov/extremes/records/.

Monthly Temperature and Precipitation Departures Since 2011 in Illinois

Here are the statewide Illinois monthly temperature and precipitation departures from the 1981-2010 average for both 2011 and 2012. We have had a run of above-average temperatures since October 2011 and a run of below-average precipitation since January of 2012. The latest outlooks published on June 30 by the National Weather Service shows that the odds of this pattern of warmer and drier conditions to prevail through July (bottom figure).

Statewide temperature departures (F) from the 1981-2010 average in Illinois for 2011 and 2012. Red is warmer than average. Blue is cooler than average. Click to enlarge.

Statewide precipitation departures (F) from the 1981-2010 average in Illinois for 2011 and 2012. Blue is wetter than average. Yellow is drier than average. Click to enlarge.

Outlooks for July and July-September as provided by the National Weather Service. Click to enlarge.

Fort Armstrong Weather Records (1820-1836)

This semester a University of Illinois Department of Atmospheric Science student, Lauren Graham, worked to make available scanned images of the weather records for Fort Armstrong that cover the period 1820 to 1836. Fort Armstrong was located at the present-day Rock Island Arsenal. The original records were maintained and scanned by staff at the Rock Island Arsenal Museum.
These are the oldest official weather records that I have been able to find for Illinois. The records contain daily temperature readings taken at 7 am, 2 pm, and 9 pm, as well as comments on the weather. My favorite is a note in the first month about a “violent hurricane” on July 21 1820 (see image below). I’m sure it was not really a hurricane but either a tornado or severe thunderstorm with high winds.
Here is the press release of the story.
Here is the Fort Armstrong page containing the images and preliminary analysis.
The plans are to introduce more analysis of these data over the summer.

Fort Armstrong, July 1820. Note the comment on July 21 about the “violent hurricane”. Click to enlarge.

Warm and Dry for May in Illinois

May 2012

A glance at the forecast for Memorial Weekend shows near record-breaking temperatures in Illinois. Already the statewide average temperature for May 1-22 is 66.1 degrees, and 3.7 degrees above average. It is now in 19th place as far as the warmest May on record. We will see how that changes over the weekend and into next week.

Monthly Temperatures Since 2011

Below are the temperature departures in Illinois since the beginning of 2011. The statewide average temperature in every month in 2012 has been above average in Illinois. As a result, we are now at 48.4 degrees for the period of January – May 22. That makes this January-May the warmest on record. It beats second place by a full 1.1 degrees (47.3 degrees set in 1921). Statewide records go back to 1895. By the way, the summer of 1921 was about 3 degrees above average with average precipitation.
The streak of warmer than average temperatures extends back to October 2011. Also, eight of the 12 months in 2011 had above average temperatures.

Statewide monthly temperature departures for Illinois in 2011 and 2012. Blue bars mean cooler than average. Red bars mean warmer than average. Average is the 1971-2000 statewide average. Illinois State Water Survey 2012. Click to enlarge.