Month: April 2012

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April Colder Than March – A Rare Case

Temperature

The statewide average temperature for April 2012 was 54.1 degrees, based on available data. The statewide average temperature for March was 55.0 degrees, based on the latest numbers from NOAA.  That means that April was almost a degree cooler than March. What makes this even more impressive was that the April temperatures are still 2.4 degrees above normal!
By the way, the statewide normal monthly temperature is 40.7 degrees for March and 51.7 degrees for April, an eleven degree rise.
How rare is it for April to be colder than March? In the statewide records that extend back to 1895, it happened only in 1907 when the March temperature was 47.0 degrees and the April temperature was 43.2 degrees. In all the other cases between 1895 to 2011, April was always warmer.
The highest temperature reported in the state for April was 92 degrees at Kaskaskia on April 2 and at Jacksonville and Pana on April 3. The coldest temperature reported was 23 degrees at Jerseyville on April 17.

Precipitation

The statewide average precipitation was 3.32 inches. That is about 0.5 inches below normal. The rainfall over the weekend was fairly widespread and helped much of the state. In general, the heaviest rains of 5 inches or more fell east of St. Louis. Meanwhile, rainfall amounts of 2 inches or less fell in far southern Illinois, far northwestern Illinois, and a large swath between Peoria and Kankakee. Those areas were 1 to 3 inches below normal for the month (second map).
The highest monthly rainfall total reported in Illinois for April was a CoCoRaHS observer near Belleville (IL-SC-3) with 8.64 inches. Some of the lowest monthly rainfall totals in the state were in Kankakee and Will Counties. For example, Grant Park (IL-KK-19) in Kankakee County reported all 30 days and only received 0.83 inches for the month.

April rainfall totals, based on a radar product developed by the National Weather Service. Click to enlarge.

April rainfall departure from normal, based on a radar products developed by the National Weather Service. Click to enlarge.

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Latest Soil Moisture and Drought Monitor for Illinois

Observed Soil Moisture

The Illinois State Water Survey has been monitoring the soil moisture at 19 sites around the state. The soil moisture is measured with probes set at specific depths at each site. It is reported as the fraction of water in the soil by volume. Most of the non-sandy soils in Illinois can hold up to 30-40 percent water by volume in the spaces between the soil particles.
Current observations in the driest areas of the state show significant declines at 2, 4, and 8 inches since early March. At the Peoria site, in the heart of the dry area, the fraction of water in the soil is only 15 percent at 2 inches, 18 percent at 4 inches, and 22 percent at 8 inches. The 20-inch depth has remained unchanged at 32 percent. By comparison at the end of April of last year, the fraction of water in the soil at those depths were all in the 35-40 percent range.
We are in the process of getting these data online in the next few weeks. Stay tuned.

U.S. Drought Monitor

The latest U.S. Drought Monitor map for Illinois shows an expanded area of D0 “abnormally dry” weather across the central part of the state between Interstates 70 and 80. A small area of D1 “moderate drought” is located in the area centered on Logan County. Another small area of D0 is in southeastern Illinois.

Here is what the U.S. Drought Monitor says for Illinois. Click to enlarge. Link to original (updated weekly). Released on April 26, 2012.

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Dry Weather Across the Eastern Corn Belt

If you look at the Corn Belt this spring you see two different stories. Much of the western Corn Belt has enjoyed above normal rainfall if you look at the last 30 and 90 days (first two maps below). However, below normal rainfall was common across much of Illinois, and parts of Indiana, Ohio, Kentucky and southeastern MO. Those areas have widespread rainfall departures of 2 to 4 inches in the last 90 days.  A few isolated spots scattered across Illinois have departures of 4 to 6 inches.  A particularly dry spot in southeastern Illinois, southwestern Indiana, and western Kentucky has rainfall departures of 6 to 8 inches at 90 days.
This has definitely had an effect on streamflows (third map) and soil moisture (fourth map). Keep in mind that while the streamflows are low for this time of year, it is relative to the normally high streamflow in spring. The same would be true of soil moisture.
The last map shows the U.S. Drought Monitor depiction for Illinois as of April 17 with a large swath of “abnormally dry” conditions across central and southeastern Illinois.
There are some opportunities for rainfall between now and Saturday but the expected amounts are modest at 0.5 to 1.0 inches total. In the past few weeks, the forecasts have been overly optimistic about rainfall amounts. This is likely the result of the soils drying out, cutting off the local source of atmospheric moisture (humidity).

The 90-day precipitation departure for the Midwest, ending on April 24, 2012. Click to enlarge.

The 30-day precipitation departure for the Midwest, ending on April 24, 2012. Click to enlarge.

The 7-day average streamflow showing areas with very low flows for this time of year, USGS. The areas in the lightest tan are in the 10-24 percentile class and classified as "below normal" by USGS. The next shade darker is at the 6-9 percentile class, and is classified as "moderate hydrologic drought". The darker shade of brown is at the less than 5 percentile class and is classified as "severe hydrologic drought". Click to enlarge. Link to original (updated daily).

University of Washington's soil moisture model run for April 23, 2012. Click to enlarge. Link to original (updated daily).

Here is what the U.S. Drought Monitor says for Illinois. Click to enlarge. Link to original (updated weekly).

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April Colder Than March So Far

I realized this morning that I was wearing short-sleeve shirts in March and long-sleeve shirts (and a light jacket) in April. It’s like that movie Freaky Friday about the mother and daughter switching bodies, only in this case March and April have switched.
[updated April 25] The statewide average temperature for April 1-24 is 53.7 degrees. The statewide average temperature for March was 55.0 degrees, based on the latest numbers from NOAA.  That means that April was more than a degree cooler than March. What makes this even more freaky is that the April temperatures are still 2.6 degrees above normal!
BTW, the statewide normal monthly temperature is 40.7 degrees for March and 51.7 degrees for April, an eleven degree rise.
How rare is it for April to be colder than March? In the statewide records that extend back to 1895, it happened only in 1907 when the March temperature was 47.0 degrees and the April temperature was 43.2 degrees. In all the other cases between 1895 to 2011, April was always warmer.
Will this strange situation continue through the end of April? The forecast is for warmer temperatures Wednesday but then a return to cooler conditions afterwards. So we have a good shot at maintaining this record.