Rainfall Over the Last 2 Weeks in Illinois

 

Here are the amounts for the last week, as of this morning. The areas in purple in far southern Illinois have received between 10 and 15 inches. Areas in shades of red have received between 5 and 10 inches. The areas in orange and yellow have received between 2 and 5 inches. Areas in green in northwest IL have received between  0.5 and 2 inches.

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Here are the rainfall totals for the past two weeks. Same color scheme as before. Notice how the areas with 10 to 15 inches have expanded across much of southern IL south of Interstate 64 with a few areas just to the north.

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NWS Cooperative Observer Network rainfall totals in Illinois for the period of April 26 to May 5, 2017, ranked from high to low. Totals that have exceeded the expected 10-day, 100-year rainfall amounts for that area are in red. Continue reading

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Wet April and 2nd Warmest January-April on Record for Illinois

Precipitation: The statewide average precipitation for April in Illinois was 7.01 inches, 3.23 inches above normal and the 2nd wettest April on record. Here are the top five wettest Aprils. Notice a pattern? Three out of the five have been since 2011.

  1. April 2011 – 7.62 inches
  2. April 2017 – 7.01 inches
  3. April 1957 – 6.99 inches
  4. April 2013 – 6.93 inches
  5. April 1927 – 6.87 inches

The largest monthly total for April in Illinois was Carbondale with 14.41 inches. Several other sites in southern Illinois had similar amounts including Bush (Williamson County) with 13.63 inches, West Frankfort (Franklin County) with 13.35 inches, Kaskaskia (Randolph County) with 13.34 inches, and Murphysboro (Jackson County) with 13.02 inches.

Temperature: The statewide average temperature for April was 56.4 degrees, 3.8 degrees above average and the 11th warmest April on record. The warmest reading for April was 89 degrees at Kaskaskia on April 20.  The coldest reading for the month was 19 degrees at Morrison on April 10.

Statewide records of temperature and precipitation go back to 1895.

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Here are the temperature departures for 2017. As you can see, every month in 2017 has been well above normal. So far this January-April is the 2nd warmest such period on record with a statewide average temperature of 43.2 degrees, 5.4 degrees above normal. Only 2012 was warmer at 44.5 degrees, 6.7 degrees above normal. [corrected from an earlier version]

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Widespread, heavy rains possible over next week in Illinois

As of April 25, the statewide average precipitation for Illinois is 2.8 inches, which is 94% of normal. However, we have several opportunities for widespread rains this week and into the weekend, according to the NWS precipitation forecast.

The first round of rain on Wednesday and Thursday has potential rainfall amounts of 1 to 2 inches across most of Illinois, along with the chance for severe weather. Continue reading

5-Day Rainfall in Illinois and Midwest

Here are the 5-day accumulated rainfall totals for Illinois and the Midwest. Rainfall was heaviest south of Interstate 70 where amounts of 4 to 8 inches were common (lighter shades of blue). The largest 5-day rainfall total was from a CoCoRaHS station at Waltonville (IL-JF-2) with 10.79 inches. CoCoRaHS is a national network of trained volunteer precipitation observers, learn more at cocorahs.org

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100-Year Storm Strikes Illinois State Fair

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Radar-estimated rainfall from August 12 storm.

The 5.59 inches of rain reported at the Springfield Airport on Friday night fell in 6 hours. This represents the 100-year storm for that duration in central Illinois, according to Bulletin 70. The results were dramatic, as reported by the Springfield Journal Register.

The concept of the 100 year storm is commonly used by engineers for assessing the risk of heavy rainfall. The 100-year storm is more completely described as the storm expected to have a return period of once every 100 years on average. The phrase “on average” being key. It does not mean the storms are exactly 100 years apart. Instead it means that if you look at rainfall statistics long enough the average frequency of such a storm would be 100 years. Unfortunately, we don’t have hundreds of years of rainfall data. Instead we estimate the values based on fitting a statistical model to the observed data.

While the phrase “100-year storm” is eye catching, it does not do a good job conveying the risk of such an event. A better way of describing it would be the “1% chance storm”, Continue reading

Heavy Rains on August 12-15

As forecasted by the National Weather Service, heavy rains have fallen across Illinois since Friday. Here are the totals by day and for the three days combined. More rain is expected today and tomorrow (last map). Friday’s rainfall is shown on the 24-hour totals for the morning of August 13, etc. We have had a stationary front parked over Illinois since Friday, which is usually a key ingredient for getting significant rainfall amount.

Here is the set of maps showing the rainfall totals for each day, using rain-gage calibrated rainfall totals. It provides a higher level of details with fairly good accuracy. The downside is that the color scale changes slightly from map to map.

Rainfall totals for the morning of August 13, 2016

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Morning of August 13, 2016.

Rainfall totals for the morning of August 14, 2016

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Flooding – Deadly Risk in Illinois with 28 Deaths in 19 Years

Right now the attention is on the widespread flooding in Texas and Oklahoma, with the number of deaths sitting at 21 and climbing. Illinois has been faced with deadly flooding in the past. An examination of the national storm database reveals that Illinois has had 28 flood-related deaths in the last 19 years*.

Here are the numbers by year in Illinois. Some years like 2000, 2008, 2009, and 2013 were especially bad with 4 to 5 deaths each. A few years had no deaths, including 2004-07, 2012, and 2014. While not part of this database, six deaths were reported in Illinois during the 1993 flood, according the ISWS report.

Flood-related deaths in Illinois from 1996 to 2014, based on data from the National Climatic Data Center.
Flood-related deaths in Illinois from 1996 to 2014, based on data from the National Climatic Data Center.

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