New Online Map Tracks Freezing Temperatures, Illinois State Water Survey

ISWS Press Release

For Immediate Release May 18, 2011
New Online Map Tracks Freezing Temperatures
Steve Hilberg - (217) 333-8495,
Lisa Sheppard - (217) 244-7270,

The Midwestern Regional Climate Center (MRCC) in the Illinois State Water Survey, a division of the Prairie Research Institute at the University of Illinois, has provided a new tool for users to glean information on the occurrences of freezing temperatures to help assess the vulnerability of spring flowers and plants.

Located on the Midwest Climate Watch page (, the freezing temperatures map is updated daily. Each weather station that records a minimum temperature equal to or less than 28 degrees is marked with a small black dot. Once a station records at least one day with a minimum temperature greater than 28 degrees F, it is marked by a large dot filled with a color determined by the date of the last freeze.

If a station has recorded a minimum temperature greater than 32 degrees in each of the past 14 days, the station is marked with an open circle with the color representing the date of the last freezing temperature.

“The changing symbols are intended to deemphasize the areas that are still freezing every day and those that have been above freezing for a period of time,” said Steve Hilberg, director of MRCC. “They also make it easier to determine if it has been some time since the last freeze.”

The map also includes shading to represent the areas that have accumulated at least 150 growing degree days, or the amount of heat accumulation used to predict plant development rates such as when plants will bloom.

“The implication of the shading is that plant development in these areas may have occurred to the extent that another freeze could damage vegetation,” Hilberg said.

Another new map on the Midwest Climate Watch web page is a 24-hour county-level soil moisture map. The site also includes month-to-date maps of temperature, snowfall, snow depth, and growing degree days.

Each week the MRCC posts a narrative of the previous week's temperatures, precipitation, and weather events. The narrative describes the impacts of these events, generally gleaned from news accounts. Narratives are archived and are searchable by event type, such as drought or storm, and state.

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