Key points
- Conditions are expected to lean warm and wet through the rest of April.
- Growing degree days are accumulating ahead of schedule.
- Active weather is expected in the next 7 days.
Past weather
Since March 1, temperatures across the state have been around 2-6 degrees warmer than normal. In the past two weeks, temperatures have stayed closer to normal, reaching 0-3 degrees below normal in some areas. Since April 1, the entire state has received below-normal precipitation. The greatest precipitation deficit exists in a band across the state starting in the southwest and extending to the northeast.
Above-normal temperatures for most of the state so far in 2025 have allowed for a greater-than-normal accumulation of growing degree days (GDDs) from January 1 to April 15. In Ames, the accumulated GDD departure is just over 100 on April 15th, and the 2025 GDDs are above the climatology. With GDDs accumulating sooner in the year, some pest emergence may happen sooner. The spring leaf index provided by the National Phenology Network shows that leaf emergence is around 15-20 days early for most of Iowa.
Red flag warnings are issued when conditions are conducive for fires: warm temperatures, low humidity, and high wind. Year to date, 23 red flag warnings have been issued within Iowa. By this time in 2024, 27 red flag warnings were issued.
Climate outlook
In the next 7 days, precipitation totals are expected to be from 0.25-2.00”, with the smallest totals in the northwest corner of the state. There is at least a 5% risk of rainfall exceeding flash flood guidance (“Marginal Risk”) for the southern and eastern parts of the state on
Sunday, April 20th through Monday, April 21st. More information can be found at the Weather Prediction Center.
Outlooks from the Climate Prediction Center provide insight into general conditions in the coming weeks. The 6–10-day outlook issued on April 15th and valid for April 21-25 shows temperatures leaning slightly above normal and precipitation leaning above normal. The 8–14-day outlook issued on April 15th and valid from April 23-29 shows temperatures continuing to lean above normal and precipitation leaning above normal. The 3–4-week outlook takes us through the end of April into the beginning of May, with temperatures leaning slightly above normal and precipitation leaning above normal. We can expect a fairly active weather pattern in the second half of April, bringing some much-needed rain, though it will interfere with crop management and planting.
4-inch soil temperatures continue to fluctuate but are forecasted to stay above 45 degrees for most of the state in the next 2 weeks. Additional moisture in the soil from the expected rainfall in the next 7 days will help maintain soil temperatures. Moist soils take longer to warm or cool compared to dry soils.
Agricultural impacts
The windy spring has certainly slowed down some agricultural activity, reducing the days available to burn prairies, apply anhydrous, spray pre-emergence herbicides, and can cause reduced visibility from blowing soil during tillage.
The risk of freeze is not entirely over, based on climatological observations. The following map shows the percent of years (based on National Weather Service and Iowa Environmental Mesonet daily estimate data) with 1 day with a low temperature less than 32 degrees between April 16 to May 16. It shows that, especially in northern Iowa, 80% or more years have had a low temperature below 32 degrees between April 16-May 16. While the outlooks lean warmer for the next few weeks, keep in mind these outlooks do not differentiate between the daily high and low temperatures.
Alfalfa weevil egg hatching begins at 300 GDDs with a base temperature of 48 degrees. Since GDD accumulation is ahead of schedule, southern Iowa is starting to see some alfalfa weevil hatching where GDDs have exceeded 300. Peak larval feeding for alfalfa weevil happens at 575 GDDs.
