A derecho blew across Iowa but farmers had 5.7 days suitable for fieldwork during the week ending Aug. 16, according to the USDA, National Agricultural Statistics Service. Dry conditions continued to be a concern for most of the state. High winds experienced on Monday caused considerable damage to on- and off-farm grain storage in their path as well as other structures. The level of crop damage reported varied widely depending on location and wind strength.
Topsoil moisture condition across Iowa rated 20 percent very short, 36 percent short, 42 percent adequate and 2 percent surplus. Ratings in west central Iowa were 45 percent very short, 36 percent short, and 19 percent adequate. The state’s topsoil moisture condition remained over half short to very short although it improved slightly.
Subsoil moisture condition statewide rated 17 percent very short, 36 percent short, 46 percent adequate and 1 percent surplus. Ratings in west central Iowa were 40 percent very short, 41 percent short, and 19 percent adequate. The state’s subsoil moisture condition also remained over half short to very short.
Corn was 81 percent in the dough stage or beyond, almost two weeks ahead of the previous year and five days ahead of the 5-year average. Just over one-quarter of the corn crop is in or beyond dent stage, 11 days ahead of the previous year and 3 days ahead of average. Corn condition rated 59 percent good to excellent, a drop of 10 percentage points from the previous week and the lowest level this crop season.
Soybeans were 97 percent blooming or beyond, three days ahead of average. Soybeans setting pods were over two weeks ahead of last year and one week ahead of average at 90 percent. Soybean condition fell again this week, and the crop is now rated 62 percent good to excellent, the lowest level so far this season.
Alfalfa hay second cutting was 97 percent complete, four days ahead of last year but one day behind the 5-year average. Just over half of the third cutting is complete, 10 days ahead of the previous year. Pasture condition fell to just 33 percent good to excellent.
Iowa preliminary weather summary provided by Justin Glisan, Ph.D., state climatologist Iowa Department of Agriculture and Land Stewardship – A powerful line of severe thunderstorms, known as a derecho, brought widespread agricultural and structural damage across rural and urban areas of Iowa on Monday, Aug. 10. Moderate to heavy rain also fell along the path of the derecho with scattered thunderstorms over the next few days. Dryness persisted around much of the state with deficits on the order of an inch. Sections of central Iowa reported up to an inch of above average rainfall with locally higher amounts. Slightly warmer conditions were also observed across much of Iowa with the statewide average temperature of 72.9 degrees, 1.1 degree warmer than normal.
Thunderstorms moved through eastern Iowa during the late afternoon hours on Sunday, Aug. 9, before clearing the state. Behind the system, cloud cover cleared with a southerly wind pushing daytime highs into the upper 80s and low 90s. Rain totals were heaviest in northwest Iowa with widespread amounts above 0.50 – 0.75 inch. A handful of stations also reported totals above one inch with Guttenberg Lock and Dam (Clayton County) reporting 1.32 inches.
Monday, Aug. 10, will go down as a significant weather day in state history. A derecho, which is a convectively initiated straight-line windstorm, propagated through Iowa’s central west-to-east corridor. This derecho was one of the strongest and most widespread to hit Iowa. Damage to crops, grain bins and structures was catastrophic with millions of acres of damaged corn and soybeans.
Urban areas from Des Moines (Polk County), Cedar Rapids (Linn County) to the Quad Cities reported substantial and long lasting power outages along with severe damage to trees and structures from extremely strong sustained winds.
Preliminary wind gusts along the derecho’s path ranged from 58 mph to well over 100 mph; according to the National Weather Service, “maximum recorded wind speeds were around 110 mph over portions of Benton and Linn Counties in eastern Iowa.” Midway (Linn County) observed the fastest wind speed of 112 mph. Moderate to heavy rain fell across sections of Iowa with general totals above 0.50 inch and locally heavier amounts in eastern Iowa; a rain gauge in Hopkinton (Delaware County) recorded 2.23 inches while the statewide average was 0.40 inch.
Calm conditions returned on Tuesday with sunny skies and afternoon temperatures in the low 80s.
Overnight lows on Wednesday, Aug. 12, were also comfortable, ranging from the upper 50s north to upper 60s south. Light showers moved into western Iowa over the early morning hours, then into portions of west central Iowa before dissipating later in the day; rain amounts were under a tenth of an inch. Warm and humid conditions built back in to the state with highs reaching into the upper 80s under hazy skies. Morning lows remained warmer than average, by up to nine degrees in western Iowa, dropping only into the low 70s.
Thursday was another warm day with highs in the mid to upper 80s; some 90 degree readings were observed in southern Iowa. Skies were clear to mostly sunny with a few passing cumulus clouds and a southerly wind. Conditions on Friday, Aug. 14, were near seasonal, generally in the mid-80s.
A cold front slowly moved into Iowa during the later afternoon and evening hours, bringing a few stronger storms into western Iowa. The front re-fired showers and thunderstorms from the northeast into central Iowa overnight into Saturday. The highest totals were reported in Des Moines, ranging from 0.80 to 1.22 inches. Widespread rain also fell through northeastern Iowa, though common totals were around a few tenths of an inch. Northerly winds, sunny skies and highs in the upper 70s and low 80s lent to a very pleasant day. Overnight lows into Sunday, Aug. 16, were cooler than average, in the mid 50s to low 60 with the statewide average low of 55 degrees, five degrees below normal.
Weekly precipitation totals ranged from no accumulation at several stations in southwest Iowa to 2.40 inches in Story City (Story County). The statewide weekly average precipitation was 0.67 inch while the normal is 0.96 inch. Burlington Municipal Airport (Des Moines County) reported the week’s high temperature of 94 degrees on Aug. 10, 9 degrees warmer than normal. Spencer Municipal Airport (Clay County) reported the week’s low temperature of 48 degrees on Aug. 15, 11 degrees cooler than normal.
