With warm weather seemingly stationary across the Midwest, many people are wondering if we have seen the last of freezing temperatures.  Climatology tells us that there is still the possibility for a late freeze, according to the Midwestern Regional Climate Center at the Illinois State Water Survey (ISWS).

Throughout the region, mid-March temperatures were generally 20 to 30 degrees above normal for this time of year.  As a result, thousands of high temperature records have been broken in March.  More than 5,000 daily high temperature records (including both minimum and maximum temperature) have been set or tied, with hundreds of them also setting records for the warmest temperature for any March date.  Some of the records were broken by 15 to 20 degrees.

 
Figure 1.

In addition to the astonishing number of daily and monthly record highs, there are other significant records being broken as well.  Much of the Midwest is on its way to seeing the warmest March on record, rivaling records that date back to the late 1800s or early 1900s.  Many stations also set records for the longest stretch of consecutive days with daily record highs in March, earliest occurrence of 80-degree weather, most consecutive days above 80 degrees in March, or most March days above 80 degrees.

The warm temperatures and relatively dry soil have prompted farmers to think about planting their corn crop early this year.  There are reports of farmers planting corn in Illinois, Iowa, and Missouri about two to four weeks early.  In addition, residential gardeners may also plant early because of the warm temperatures.

Despite the early warmth, climatology tells us that the possibility for a freeze in April remains high, putting early emerging crops and plants at risk.  Using climate data from the years 1981 to 2010, the median and earliest start of the growing season (the last spring freeze is by definition the start of the growing season) can be examined.

The median date of the beginning of the growing season is determined such that in half of the years, the growing season began before this date and half began after this date.  The median dates for the start of the growing season range from April 1 to 10 in the southern Midwest to June 1 to 10 in the northern Midwest (see Figure 1).

The earliest start of the growing season is the year (from 1981 to 2010) with the earliest date for the last spring freeze.  The earliest start to a growing season has occurred in late March across widespread portions of Missouri, Kentucky, Illinois, Indiana, and southeast Iowa.  A majority of Iowa, Minnesota, Wisconsin, Michigan, and Ohio have not experienced a growing season that has started before April (see Figure 2).

Planting crops right now warrants caution, since there is still a possibility for a 32-degree freeze to occur, or even a 28-degree “hard” freeze, which could kill plants that have emerged.  Crop insurance policies do not cover replanting costs if farmers plant before the earliest seeding date, which is April 6 in most of Illinois, Indiana, and Ohio and April 11 in Iowa and Minnesota.

 
Figure 2.

Spring freeze maps (32-degree and 28-degree) are available from the Midwestern Regional Climate Center for the central portion of the United States, including Ohio, Kentucky, Michigan, Indiana, Illinois, Wisconsin, Missouri, Iowa, Minnesota, North Dakota, South Dakota, Nebraska, Kansas, Colorado, and Wyoming.  The maps are available on the Midwest Climate Watch website (http://mrcc.isws.illinois.edu/cliwatch/watch.htm).

Besides early planting, the warm temperatures are causing a variety of other impacts across the Midwest.  The unseasonably warm and dry conditions in parts of the Midwest have increased the risk for wildfires in Minnesota and Wisconsin.  However, rain over the past few days should ease the risk for wildfires in parts of this region.

Ice break-up on lakes in Minnesota has occurred in the southern half of the state two to four weeks early, according to the Minnesota State Climatology office.  Early ice break-up is also occurring in other parts of the Midwest.  This winter season, lakes near Madison, Wisconsin experienced the fifth shortest duration of ice cover on the lakes since records began in 1852.

Apple and peach trees are blooming in Missouri, Wisconsin, Iowa, and Illinois.  The last year fruit trees bloomed this early in the Midwest was in 2007, which resulted in a late freeze on Easter weekend (http://www.ncdc.noaa.gov/special-reports/2007-apr-cold-event.html), an event that is now leaving orchard owners nervous that a similar freeze could happen again this year.  The warm nighttime temperatures are also inhibiting the production of syrup from maple trees in Wisconsin.

The Iowa State Climatologist, Missouri State Climatologist, Wisconsin State Climatology Office, Quad Cities NWS, and Grand Forks NWS also contributed to this press release.

The Midwestern Regional Climate Center is a cooperative program of the Illinois State Water Survey and the National Climatic Data Center (National Oceanic and Atmospheric Administration, U.S, Department of Commerce).