On Monday August 10, 2020, a powerful weather system known as a derecho (pronounced “deh-REY-cho”) impacted nine states from South Dakota to Ohio (Figure 1). The National Weather service defines a derecho as a long-lived windstorm that produces widespread damage like a tornado but in one direction along a straight path or "straight-line wind damage." Last week’s derecho was exceptionally damaging to agricultural interests, particularly in Iowa. Numerous reports of winds stronger than 70 mph were noted with an unofficial gust to 106 mph at Le Grand. According to the Iowa Soybean Association, the latest USDA reports suggests 14 million impacted crop acres with $6 billion in liability losses. Only minor damage was reported in northwest Ohio as the derecho weakened below severe limits Monday evening, but it brought a decent round of rainfall to the area. The last major derecho to occur in Ohio was on June 29, 2012 which brought 22 fatalities from Illinois to the Mid-Atlantic and $2.9 billion in losses.
Figure 1: Preliminary storm reports associated with the August 10, 2020 derecho.
Although the last couple of weeks have featured multiple rounds of showers and storms across Ohio, much of the state has seen below average precipitation. Rainfall amounts of 2-3” have been scattered across counties in northwest, southwest, and south-central Ohio, with some locations picking up even greater totals (e.g., 3.98” near Archbold in Fulton County). As of Thursday August 13, 2020, the U.S. Drought Monitor indicates ~71% of the state is currently experiencing abnormally dry to moderate drought conditions, with the driest areas located across Madison, Pickaway, Richland, Wayne, Stark, Belmont, and Jefferson Counties. Soil moisture remains depleted along with low flows on streams in these areas. If you are seeing drought impacts in your area, consider submitting a report to the Drought Impact Reporter. For more information on recent climate conditions and impacts, check out the latest Hydro-Climate Assessment from the State Climate Office of Ohio.
While a slight chance for an isolated storm continues through Tuesday, drier and cooler air will be in control for much of the week ahead. Highs will generally range from the mid-70s to the low-80s (north to south) on Tuesday and Wednesday, slowly warming back into the 80s statewide by the weekend. Overnight lows this week will dip into the low to mid 50s for many as well. A few storms may develop as we end the weekend into early next week. Overall, precipitation will be on the light side (Figure 2), with less than 0.10” expected (locally heavier rainfall possible).
Figure 2: Forecast precipitation for the next 7 days. Valid from 8 pm Monday August 17, 2020 through 8 pm Monday, August 24, 2020. Figure from the Weather Prediction Center.
The latest NOAA/NWS/Climate Prediction Center outlook for the 8-14 day period (August 25 – 31) and the 16-Day Rainfall Outlook from NOAA/NWS/Ohio River Forecast Center show slightly elevated probabilities for above average temperatures and above average precipitation (Figure 3). Normal highs during the period are in the low to mid-80s, lows in the low to mid-60s, with 0.85-1.05” of rainfall per week. From a drought perspective, this is likely to maintain current conditions.
Figure 3: Climate Prediction Center 8-14 Day Outlook valid for August 25-31, 2020 for (left) temperatures and (right) for precipitation. Colors represent the probability of below, normal, or above normal conditions.