Hail and Damaging Winds in Iowa, April 15, 1994

The seasons first significant convective outbreak occurred during the evening hours of the 14th. The situation was similar to several others that occurred during the early spring with the exception that the moisture made it into the system in advance of the dynamics. Low pressure moved across Kansas and headed northeast into Iowa during the late afternoon and early evening hours. A warm front extended east from the low. To the south of the front was moist and very unstable air. The upper air sounding from the evening of the 14th from Topeka, Kansas indicated considerable instability. It revealed a CAPE (convective available potential energy) value of over 2600 J-Kg-1. Other indices also showed a great deal of instability. During the early evening, a strong southerly low level flow transported this moist and unstable air into Iowa. Thunderstorms erupted explosively over southwest Iowa during the early evening hours. What began as an area over the southwest counties rapidly developed northeast across the rest of the state. Severe weather was widespread from southwest through central into east-central Iowa. During the later evening hours, the entire area of thunderstorms sagged southeast into the moisture feed. Many of the storms produced winds of 35 to 50 mph and almost all produced at least pea- to marble-size hail. By far, the most significant severe weather feature with the storms was the hail. High winds from some of the storms resulted in damage and overturned tractor-semitrailers. Four tractor-semitrailers were overturned on Interstate 29 west of Mondamin by 65 to 70 mph winds. High winds later in the evening hours resulted in damage over eastern Iowa. Winds gusted to around 75 mph at Ryan. A pole barn was destroyed and a large barn knocked off of its foundation there. Damage was reported at other locations around the state by winds in the 60 to 70 mph range. An example was a barn that was destroyed by winds between Milton and Cantril in Van Buren County. Many tin construction buildings were damaged or destroyed. Serious wind damage occurred across the central part of the state. During the mid evening hours the storms developed into a bow echo configuration. The bow echo formed near central Iowa in Madison County. The bow echo then accelerated northeast across Dallas and Story Counties before breaking apart. Storm centroid movements from the WSR-88D radar at Johnston indicated the movement increased from 30 to 35 mph to around 55 mph within the bow echo. A broad swath of damage occurred with the bow echo. In the early stages, what appeared to be a gust front, or gustnado, touched down briefly in Macksburg. The first widespread damage from it was in Madison County south of Booneville. High winds of around 90 to 95 mph flattened two houses, 10 barns, and numerous out buildings. Damage in the area was estimated at $500,000 to $600,000. The same storm damaged two buildings and destroyed two large grain bins near Winterset a short time earlier. The high winds swept northeast into the Booneville area, where a farmstead was damaged. Sixty to seventy thousand dollars damage occurred to the farmstead. Structural damage occurred to the farm house and the ends were blown out of the barn. Debris was strewn across the road. The high winds continued northeast and could be traced into southern Story County. The damage path from the bow echo was about 10 miles wide. As the storm system crossed Interstate 35, at least five cars were blown off the road and two tractor-semitrailers were overturned at the 105 mile marker. The drivers of the two trucks sustained minor injuries, but did not require hospitalization. Farther north, damage was reported in the Ames area. A tractor-semitrailer was overturned just south of Ames and several grain bins were downed west of town. The bow echo eventually broke up, but scattered reports of high winds continued into Tama County and farther northeast. Hail accompanied most of the storms. All along the path of the bow echo metal buildings were damaged or flattened. Tin from them was strewn along fields downwind from one-half to one mile. Many areas reported 0.75- to 1.50-inch diameter hail. The most significant hail occurred over southwest Iowa with the initial development and with the bow echo. Golf ball-size hail pelted Cass, Pottawattamie, and Mills Counties. The largest hail reports came from Cass and Adair Counties. Three-inch diameter hail was reported southeast of Griswold in Cass County and south of Adair in Adair County. VIL (Vertical Intergrated Liquid) values from the WSR-88D were as high as 77 Kg-M-2 were indicated. Large hail also occurred with the bow echo. Numerous reports of up to golf ball-size hail were received with its passage. Over the northern sections of the Des Moines metropolitan area, baseball-size hail was reported. As the entire area of storms advanced east, the size of the hail dropped off. Reports over eastern Iowa were generally around 0.50- to 0.75-inch. Hail damage was mainly to property. Significant damage occurred to cars as well as roofs due to the hail. Crop damage was limited as most of the crop had not yet been planted. Some damage occurred to winter wheat and oats over the southwest counties, however. Two other tornadoes occurred. The first was with the cells over western into central Iowa. One of them took on more of a supercell structure and spawned a brief tornado touchdown in the Fontanelle area. Damage was minor with this tornado as it traversed open country. Another tornado touched down in Marshall County north of State Center. It caused damage at one farm stead there. A barn was destroyed, a metal machine shed damaged, another shed moved off of its foundation, and some structural damage to two houses there. Several trees were snapped off as well as a one permanent road sign. Lightning struck a house in Des Moines as the line passed. Lightning blew a hole in the roof and caused a small fire. Damage was about $3,500. During the later evening hours, the thunderstorms propagated east. At the same time another area of thunderstorms developed and moved northeast out of Missouri. As these storms moved across eastern Iowa, spotty wind and hail damage was reported. Hail was generally around three-quarters of an inch or just above in diameter. Gusty winds occurred with all of the storms, but most of the damage occurred in Delaware and Clinton Counties. High winds caused roof damage in Grand Mound, and tore the roof off of a building in Elwood. Both of these were in Clinton County.

The seasons first significant convective outbreak occurred during the evening hours of the 14th. The situation was similar to several others that occurred during the early spring with the exception that the moisture made it into the system in advance of the dynamics. Low pressure moved across Kansas and headed northeast into Iowa during the late afternoon and early evening hours. A warm front extended east from the low. To the south of the front was moist and very unstable air. The upper air sounding from the evening of the 14th from Topeka, Kansas indicated considerable instability. It revealed a CAPE (convective available potential energy) value of over 2600 J-Kg-1. Other indices also showed a great deal of instability. During the early evening, a strong southerly low level flow transported this moist and unstable air into Iowa. Thunderstorms erupted explosively over southwest Iowa during the early evening hours. What began as an area over the southwest counties rapidly developed northeast across the rest of the state. Severe weather was widespread from southwest through central into east-central Iowa. During the later evening hours, the entire area of thunderstorms sagged southeast into the moisture feed. Many of the storms produced winds of 35 to 50 mph and almost all produced at least pea- to marble-size hail. By far, the most significant severe weather feature with the storms was the hail. High winds from some of the storms resulted in damage and overturned tractor-semitrailers. Four tractor-semitrailers were overturned on Interstate 29 west of Mondamin by 65 to 70 mph winds. High winds later in the evening hours resulted in damage over eastern Iowa. Winds gusted to around 75 mph at Ryan. A pole barn was destroyed and a large barn knocked off of its foundation there. Damage was reported at other locations around the state by winds in the 60 to 70 mph range. An example was a barn that was destroyed by winds between Milton and Cantril in Van Buren County. Many tin construction buildings were damaged or destroyed. Serious wind damage occurred across the central part of the state. During the mid evening hours the storms developed into a bow echo configuration. The bow echo formed near central Iowa in Madison County. The bow echo then accelerated northeast across Dallas and Story Counties before breaking apart. Storm centroid movements from the WSR-88D radar at Johnston indicated the movement increased from 30 to 35 mph to around 55 mph within the bow echo. A broad swath of damage occurred with the bow echo. In the early stages, what appeared to be a gust front, or gustnado, touched down briefly in Macksburg. The first widespread damage from it was in Madison County south of Booneville. High winds of around 90 to 95 mph flattened two houses, 10 barns, and numerous out buildings. Damage in the area was estimated at $500,000 to $600,000. The same storm damaged two buildings and destroyed two large grain bins near Winterset a short time earlier. The high winds swept northeast into the Booneville area, where a farmstead was damaged. Sixty to seventy thousand dollars damage occurred to the farmstead. Structural damage occurred to the farm house and the ends were blown out of the barn. Debris was strewn across the road. The high winds continued northeast and could be traced into southern Story County. The damage path from the bow echo was about 10 miles wide. As the storm system crossed Interstate 35, at least five cars were blown off the road and two tractor-semitrailers were overturned at the 105 mile marker. The drivers of the two trucks sustained minor injuries, but did not require hospitalization. Farther north, damage was reported in the Ames area. A tractor-semitrailer was overturned just south of Ames and several grain bins were downed west of town. The bow echo eventually broke up, but scattered reports of high winds continued into Tama County and farther northeast. Hail accompanied most of the storms. All along the path of the bow echo metal buildings were damaged or flattened. Tin from them was strewn along fields downwind from one-half to one mile. Many areas reported 0.75- to 1.50-inch diameter hail. The most significant hail occurred over southwest Iowa with the initial development and with the bow echo. Golf ball-size hail pelted Cass, Pottawattamie, and Mills Counties. The largest hail reports came from Cass and Adair Counties. Three-inch diameter hail was reported southeast of Griswold in Cass County and south of Adair in Adair County. VIL (Vertical Intergrated Liquid) values from the WSR-88D were as high as 77 Kg-M-2 were indicated. Large hail also occurred with the bow echo. Numerous reports of up to golf ball-size hail were received with its passage. Over the northern sections of the Des Moines metropolitan area, baseball-size hail was reported. As the entire area of storms advanced east, the size of the hail dropped off. Reports over eastern Iowa were generally around 0.50- to 0.75-inch. Hail damage was mainly to property. Significant damage occurred to cars as well as roofs due to the hail. Crop damage was limited as most of the crop had not yet been planted. Some damage occurred to winter wheat and oats over the southwest counties, however. Two other tornadoes occurred. The first was with the cells over western into central Iowa. One of them took on more of a supercell structure and spawned a brief tornado touchdown in the Fontanelle area. Damage was minor with this tornado as it traversed open country. Another tornado touched down in Marshall County north of State Center. It caused damage at one farm stead there. A barn was destroyed, a metal machine shed damaged, another shed moved off of its foundation, and some structural damage to two houses there. Several trees were snapped off as well as a one permanent road sign. Lightning struck a house in Des Moines as the line passed. Lightning blew a hole in the roof and caused a small fire. Damage was about $3,500. During the later evening hours, the thunderstorms propagated east. At the same time another area of thunderstorms developed and moved northeast out of Missouri. As these storms moved across eastern Iowa, spotty wind and hail damage was reported. Hail was generally around three-quarters of an inch or just above in diameter. Gusty winds occurred with all of the storms, but most of the damage occurred in Delaware and Clinton Counties. High winds caused roof damage in Grand Mound, and tore the roof off of a building in Elwood. Both of these were in Clinton County.