Climate models predict a near average first fall frost date for South Dakota as cooler weather moves across the state.
“With cool air moving into the region from Canada the first week in October, it is possible that temperatures will dip below freezing,” said Laura Edwards, SDSU Extension State Climatologist.
She explained that for most of the state, the average first frost is the last week in September or early October. “The long-term trends in this region have been tending towards later first fall frost dates. In the last several years, we have seen first frost frequently occur in October, but also as late as mid-November.”
The latest U.S. Climate Outlook for October, released by the National Oceanic Atmospheric Administration (NOAA) September 20, shows the likelihood that southeastern South Dakota could be colder than average.
“Chances are very good that the early part of the month will be cooler than average, which may be enough to tilt the odds for the whole month, even if it turns warmer sometime later,” Edwards said. “The rest of the state has equal chances of colder, warmer or near average in the month ahead.”
A wetter than average growing season is one of the drivers of cooler temperatures, Edwards explained. “When soils are very wet, the air above it is often more humid than usual. Moist air and soil do not heat up as quickly as dry air, so temperatures remain more moderate in moist conditions.”
Looking ahead to October, the precipitation outlook is less certain.
Early in the month, Edwards said the models point to an active weather pattern that may continue with several small systems passing through. Later in the month, there is more uncertainty. “As a result, equal chances of overall wetter, drier or near average precipitation is projected across the north central states,” Edwards said.
However, October’s temperatures are not an indication of what South Dakotans should expect this winter, Edwards said, explaining that a weak El Niño could gradually impact our winter climate. “Historically, this has often meant warmer than average temperatures. The long-lead outlook for October through December is consistent with this pattern. It shows an increased likelihood of warmer than average temperatures for October through December and into 2019.”
The precipitation outlook for the remainder of the fall and early winter is also uncertain this year in our region. “There are no consistent signs of either wetter or drier conditions in computer-generated forecasts. Additionally, El Niño climate patterns have not been consistently tied to wetter or drier winters in the Northern Plains. As a result, the north central states currently have equal chances of these scenarios playing out at the end of this year,” Edwards said.
Climate impact on crops
Cool temperatures and wet conditions will make for a slow corn and soybean harvest season. Excess moisture could reduce quality of some crops. During this challenging time, when the grain market is low, mechanical grain drying may be required to ensure the highest quality seed possible after harvest.
However, for winter wheat growers, some moisture could be beneficial, as planting season is underway. Some of the drier areas in central and northern South Dakota need rainfall to help with germination, so a wetter pattern would be favorable.