Dennis Todey, South Dakota State Climatologist
Pat Guinan, Missouri State Climatologist
This time of year questions about frost/freeze potential are common as producers look for a little more time for crops to mature, or gardeners and horticultural interests hope for some extra days to collect a few more tomatoes. Projecting specific frost dates are difficult beyond using models out to 1-2 weeks. Thus, climatologies and current crop progress become very important.
This year, current crop progress varies greatly across the Plains and Midwest because of spring and early summer planting conditions. Early spring in the northern plains/upper Midwest was quite dry allowing easy planting progress and warm soils before rains started occurring in May. This situation was in large contrast to the southern and eastern parts of the Corn Belt.
Persistent wet weather impacted portions of the southern and eastern Corn Belt from May to July. Chronic muddiness was especially notable over much of Missouri as well as portions of Illinois and Indiana where some locations reported measureable rainfall for more than half the days between May and July. Several Missouri communities reported 16 or more days with rainfall ≥ 0.50” between May and July, double the average for the period. Missouri and Illinois observed their wettest May-July period on record.
The persistent wet conditions led to late planting over parts of Missouri, Illinois and Indiana, but Missouri dealt with the brunt of missed planting opportunities due to wetter May conditions. According to the Missouri Agricultural Statistics Service, 87% of the corn and only 23% of the soybean crop had been planted by the end of May, 8% and 34% behind the 5-year average, respectively. By mid-August, Missouri had the dubious distinction of leading the country in largest number of prevented planting acres for corn and soybean.
As of mid-September, crop progress in the northern plains is generally close to average or slightly ahead in some cases. Because of that there is less concern about freezing conditions. Iowa, Michigan and North Dakota were double digit behind in crop progress. Nebraska, South Dakota, Minnesota and Wisconsin were within 5% of average. Fortunately, unusually warm September weather across the entire Corn Belt has hastened crop maturity and current forecasts indicate no threat of an early freeze.
Current models keep temperatures warmer than average through the end of September and even somewhat likely into October over the region. The likelihood of frost/freeze is limited in this area. With another 10-14 days possible before a chance for freeze, most crops are likely to be fully mature or very close by early October in much of the northern Corn Belt areas. Thus the freeze impact may be minimized. In fact, a common recent occurrence in several years has been producers hoping for a freeze to kill off soybean stems to make harvest easier.
On the other hand, late soybean planting in the southern Corn Belt, especially across Missouri, has many farmers concerned about freeze dates. It may be well into October before soybean reaches maturity in the region. University of Missouri Extension recently released an online frost/freeze probabilities guide for Missouri. The guide provides frost/freeze probability tables, maps and dates for various temperature thresholds during the spring and fall and can be accessed at: http://ipm.missouri.edu/FrostFreezeGuide.
Additional frost/freeze information for the U.S., including current and climatological specifics, can be found at the following link: http://mrcc.isws.illinois.edu/VIP/frz_maps/freeze_maps.html.