Monitoring freeze events in spring and fall for the Central US

Spring and fall freezes mark the extent of the growing season and are important to many users, from commercial agriculture to backyard gardeners. Because individual freeze occurrences are driven largely by synoptic weather events, there are large differences in the interannual timing of such events. Monitoring freeze events in the fall is straight forward. The first fall freeze brings an end to the need for monitoring for the season as further freeze occurrences are of less consequence with plants no longer active. Spring freeze monitoring is more complicated because, at the time of the freeze, it is not known if it will be the last such event of the season. Spring freeze impact is not solely dependent on the date of the freeze but also on the weather conditions prior to the freeze. A spring freeze after a warm stretch has the potential for much more damage than a freeze after a cold period even if both events occur on the same calendar date.

The Midwestern Regional Climate Center (MRCC) recently developed monitoring products for spring and fall freeze events, each available in the appropriate season on the MRCC web site (http://mrcc.isws.illinois.edu/cliwatch/watch.htm). The products show both the current status and median freeze dates, which is helpful in putting the current status into historical context. Monitoring is done for two temperature thresholds in both spring and fall. The spring product shows the timing of the most recent freeze and a proxy for the potential of plant damage. The methodology, designed to monitor the current year in real-time, can also be utilized in retrospective examinations of past freeze events.