April Already 4th Wettest on Record

Based on preliminary data, this April in Illinois is already the 4th wettest on record with 6.58 inches of precipitation. Average statewide precipitation for April is 3.77 inches. So we are already almost two inches above average.

According to the NWS forecast, more rain is expected across southern Illinois on Friday and Saturday. Therefore, it is possible that we will move up the list by the end of the month. In addition, some sites may have already reached their record for April, including the city of Chicago.

Top 5 Wettest Aprils

  1. 2011 with 7.40 inches
  2. 1957 with 7.13 inches
  3. 1927 with 6.95 inches
  4. 2013 with 6.58 inches
  5. 1944 with 6.50 inches

Precipitation Pattern Across the State

Here is how the precipitation has been distributed around the state, based on our multi-sensor precipitation product, with the actual amounts and the departures from average. Many parts of central and northern Illinois have more than double their average April precipitation (shades of purple in the second map).

April precipitation in inches for the first 24 days of the month. Click to enlarge.
April precipitation in inches for the first 24 days of the month. Click to enlarge.
April precipitation as departures from average. Click to enlarge.
April precipitation as departures from average. Click to enlarge.

Frost in Illinois

frost2For much of Illinois April is typically the last month that we see freezing temperatures until Fall (at least we hope). Below are the maps showing the median dates when we see 28 and 32 degrees for the last time in Spring. The median represents the middle value in the range of dates and is less sensitive than the average to unusually early or late dates.

We have more discussion and maps, including the earliest and latest dates of freezes during the 1981-2010 period on our frost webpage.

In addition you can track the status of this spring (2013) in terms of how things stand on hitting 28 and 32 degrees from the Midwestern Regional Climate Center.

Click to enlarge.
Click to enlarge.
Click to enlarge.
Click to enlarge.

Snowfall Map from the March 24-25 Snowstorm

Here is a great product from the NWS (www.srh.noaa.gov/ridge2/snow/) showing the snowfall totals of the last two days. I chose the last two days since some snow from the event fell before 7 am on Sunday. The heaviest amounts were concentrated over central Illinois, including 18.5 inches at Springfield. It was very impressive for a late season snowfall. NWS Lincoln has a listing of the snowfall totals from the storm.


Cold March

I dropped my car off at the shop for some brake work this morning here in Champaign and decided to walk to work. The air temperature was 21 degrees and the wind chill was 4 degrees. That was an uncomfortable stroll even with a winter coat, hat, and gloves. A year ago this morning (March 20, 2012), the air temperature was 63 degrees and well on its way up to a high of 82 degrees, a record high for this date.

So far this year, the statewide March temperature is 33.3 degrees. A year ago through this date, the statewide temperature was 51.1 degrees. That’s a whopping 17.8 degree difference. March went on to become the warmest March on record at 55.3 degrees, 14.2 degrees above the long-term average monthly March temperature of 41.1 degrees.

The rest of March does not look promising. The 1-5 day forecast shows temperature 10 to 14 degrees below average for Illinois. The 6-10 and 8-14 day forecast show widespread cold weather across Illinois and the central US. Figures below.

The long-term average temperatures for March were calculated from the 1981-2010 period.




Spring Frost in Illinois

Frost in spring is a concern to farmers, landscapers, and gardeners. Frost in Illinois is usually not measured directly at weather stations. Instead, it is inferred from the air temperature – when the air temperature crosses the threshold of 32°F.

The average date of the last spring occurrence of 32°F ranges from April 7 in far southwestern Illinois to April 28 in northern Illinois (see map below). The actual date can vary from year to year. The spring dates are getting earlier by about 5-10 days over the last few decades.

The actual date varies from year to year. For tender plants, add two weeks to the average date in the spring to protect against late season frost.

Although 32°F is the temperature traditionally used to show frost, visible frost can be seen on the ground and objects when temperatures are slightly above 32°F on calm, clear nights that allow cold, dense air to collect near the ground. Under these conditions, the temperature near the ground actually can be a few degrees cooler than at the 5-foot height of the official National Weather Service thermometer.

Open, grassy areas are usually the first to experience frost, while areas under trees are more protected because the trees help prevent the heat from escaping. Homeowners can protect tender plants by providing this same type of protection if they cover their plants when a frost is expected. Plants near heated buildings sometimes are spared too. Because of the abundance of warm buildings and trees in towns, they tend to experience frost less often than those living in the country.

Average dates of last spring frost in Illinois.

Fourth Warmest Spring in Illinois

Based on preliminary data, the statewide average temperature for spring in Illinois was 55.3 degrees, 3.3 degrees above normal and the fourth warmest spring on record. Warmer than normal conditions prevailed in the spring months of March (+2.5 degrees), April (+6.2 degrees), and May (+1.3 degrees).

The statewide average precipitation for spring was 11.97 inches, just 0.7 inches above normal. This is notably less than the 15.83 inches that fell in the spring of 2009 and the 14.21 inches that fell in the spring of 2008.

Climatologists and meteorologists tend to use the calendar months of March-May to define spring and not the astronomical definition from the vernal equinox (usually March 20) to the summer solstice (usually June 21). The calendar months better match the climate of Illinois. Our winter weather usually diminishes by early to mid March across much of Illinois and summer weather usually arrives long before June 21.

Spring temperatures in Midwest.
Spring temperature departures for the Midwest for 2010.
Spring precipitation in the Midwest
Spring precipitation in the Midwest for 2010.

Warmest April on Record for Illinois

Based on preliminary data, the statewide average temperature for Illinois in April was 58.4 degrees, 6.2 degrees above normal and the warmest April on record. This beats the old record of 58.2 degrees set in 1955. Official statewide average temperature records go back to 1895. The warm temperatures in April were not unique to Illinois – the entire Midwest was much above normal (see map below).

April rainfall was 3.5 inches, just 0.3 inches below normal. Areas in western Illinois around received the most precipitation, over 5 inches in some locations. A CoCoRaHS observer in Matherville (Mercer County) reported 6.50 inches for the month.

April temperature departures
Temperature departures for April across the Midwest (click to enlarge).
Midwest precipitation for April
Precipitation totals for April across the Midwest (click to enlarge).