Monthly Archives: March 2012

U.S. Drought Monitor: “Abnormally Dry” to central Illinois

This week’s U.S. Drought Monitor noted a region considered “Abnormally Dry” across central Illinois. This is a result of three things: below-normal precipitation over the last 90 days, much above-normal temperatures (which have increased evaporation), and streamflows that are much below-normal for this time of year. On that last point, streams are normally bank-full and then some, so being much below-normal still means there is water flowing.

At this point, there have been no significant negative impacts reported. In the short-term, the warm, dry weather is beneficial for field work. However, it is an area that we will watch in the future.

U.S. Drought Monitor for conditions as of March 27, 2012. Click to enlarge.

Precipitation departures in Illinois over the last 90 days. Click to enlarge.

USGS supplied streamflows. Click to enlarge.

What Follows a Warm March?

What follows a warm March in Illinois? Out of curiosity I looked at the other nine years in the list of 10 warmest months of March on record in Illinois (earlier post). First, I looked at the temperature and precipitation patterns for April. Then I looked at the May-August period as the heart of the growing season. Here are the results.

Disclaimer: while past years can give some insight on how the atmosphere has behaved over Illinois, they are not always the best forecast for the upcoming month, season, or year. Each new year brings a unique set of circumstances that causes things to play out differently than any previous year.


Historically, a warm March has been followed by a colder-than-normal April on average (first map). That’s true not just in Illinois but across the U.S. On the other hand, precipitation for those same April periods was a mixed bag in Illinois (second map). Most of the state was near-normal while west-central Illinois was slightly wetter-than-normal. It is interesting that dryness shows up in Minnesota, Iowa, Nebraska, and South Dakota – an area having trouble with drought this year.

Temperature departures in April following past warm March's in Illinois.

Precipitation departures in April following past warm March's in Illinois.

May – August

The period from May through August is the core of the growing season in Illinois. Rather than produce temperature and precipitation maps of each month, I considered the entire May-August period in one set of maps. One popular question I get is “Does this warm weather now mean that we will get a hot summer?” At least historically, the growing season following a warm March does not show a pattern of above-normal temperatures. On average, they have been remarkably mild in temperature. There is a tendency towards below-normal precipitation across much of Illinois and the Midwest. It’s nothing catastrophic, on average just an inch below normal in parts of eastern and northern Illinois. Meanwhile, southern Illinois is in an area of slightly above-normal precipitation.

Growing season temperature departures following warm March's in Illinois.

Growing season precipitation departures following warm March's in Illinois.

One last note, using an average of several years together may cover up any kind of bipolar personality where half the summers were extremely hot and half the summers were extremely cold. I did not seeing anything like that in this analysis. For example, in the nine cases of the growing season temperatures, four were slightly cooler than normal, two were near normal, two cases slightly warmer than normal, and only one case (1921) was well above normal (i.e., hot).

Searching for March Records

If you are interested in daily and monthly weather records, there are a few excellent web sites that can help.

NOAA National Climatic Data Center

The NCDC site allows you to look at daily, monthly, and all-time records for sites in a selected state. Records include temperature (highest high, lowest low, etc.), precipitation, and snowfall. The report for March is especially interesting with 352 broken records and 52 tied records for sites in Illinois as of March 27. See the link to the PDF below:

Report from NCDC on record highs set in March 2012

Weather Underground

The folks at has a similar page as the NCDC site with slightly different interface and output at

On Track for Record Setting March


[updated March 30, 2012]

Based on data through March 29, the statewide average temperature was 54.7 degrees, 14.1 degrees above normal. Of course, we still have March 30-31 to go but all indications are that the much above normal temperatures will continue. So here are the ten warmest March’s in the Illinois statewide records that date back to 1895:

  1. 2012: 54.7°F (as of March 29)
  2. 1946: 51.6°F
  3. 1910: 50.9°F
  4. 1945: 50.5°F
  5. 1921: 49.1°F
  6. 1938: 48.1°F
  7. 2007: 47.6°F
  8. 1973: 47.5°F
  9. 1907: 47.0°F
  10. 1918: 46.4°F


Here are the ten warmest January-March’s in the Illinois statewide records. In this case, 2012’s hold on first place is more tenuous. Here you will notice that the 2000s are on the list three times as are the 1990s.

  1. 2012: 40.8°F (as of March 29)
  2. 1921: 39.2°F
  3. 1990: 38.7°F
  4. 1946: 38.1°F
  5. 1938: 37.6°F
  6. 1998: 37.3°F
  7. 1992: 36.9°F
  8. 2006: 36.7°F
  9. 2000: 36.7°F
  10. 1973: 35.9°F

Trouble Ahead from the Warm Weather?

Illinois has just come off its third warmest winter on record. And the warm weather continues in March. The first 7 days have been 3.2 degrees above normal and the NWS forecast for the next 14 days shows high odds of above-normal temperatures.

As a result, plants have begun to think spring is here. On the left are some daffodils in my yard in Champaign today. The blooms are just about to open. It’s the same story for the Magnolia tree at work (picture right). And this is central Illinois. Southern Illinois will be even farther along than here.Photo by Ben Woloszyn.

So what’s the problem? Well, it’s March 8 and we could still have temperatures drop into the 20s in March and April. In fact the median date for the last 28 degree reading in spring in Illinois somewhere near early to mid April in most locations. Our GIS expert Zoe produced this map (left) of the median dates in spring. Click the thumbnail to enlarge.

April Freeze of 2007

An April freeze is exactly what happened in 2007. A warm March was followed by a cold-air outbreak on Easter weekend that caused temperatures to drop into the low 20s and produced high winds.

Below is the plot of the daily average temperature from March 1 to April 30, 2007, for Illinois. There was a small stretch of warm temperatures in early March and then a long stretch in late March and early April with temperatures 10 to 20 degrees above normal. Trees and shrubs rapidly sprouted tender leaves and flowers during this warm spell. Things took a turn for the worst in early April when temperatures plummeted to 10 to 20 degrees below normal for about 2 weeks.

temperature plot for March - April 2007

That particular freeze cause over a billion dollars in damages across the Midwest and Southern U.S. to fruit crops, especially apples and peaches, as well as alfalfa and winter wheat. Here are some reports that outlined the conditions and damages.