Just after 4:30 PM Saturday, an isolated supercell thunderstorm developed over eastern Cass county and tracked northeast toward western Johnson county. As this storm crossed a warm front draped across the area, an initial radar signature of strong winds estimated at 50 mph began to organize into an area of strong rotation with the storm. A significant weather alert for strong winds was issued at 4:52PM, and mentioned that conditions were favorable such that storms could become capable of producing brief tornadoes. This alert was then upgraded to a tornado warning at 5:07PM. Shortly after, a tornado was spotted by Johnson County Emergency Management, and then by an off duty National Weather Service Employee.
National Weather Service Meteorologist along with the Johnson County Emergency manager conducted a survey of storm damage from Saturday afternoon’s tornado south of Holden near Medford. The map below shows the tornado touched down just north of 2 Highway, and tracked to the north-northeast about two miles before lifting just east of Medford. The tornado damaged two homes, a business, and several farm buildings. Shown in the photos below are a modular home which had it’s carport torn from its south wall, a barn with it’s roof blown off, and a business with its overhead door, roof, and one wall blown off. At its peak, the tornado was rated as an EF1 with top wind speeds of about 90 to 95 mph.
Storm damage pictures can be viewed by clicking on each individual image.
|Click on Images for Larger Versions
The images below show the low-topped supercell’s intensity (Image 1) and the rotation (Image 2) around the time the tornado warning was issued. The four panels represent different vertical slices of the storm, all taken at the same time. In the second image, warm colors (reds) show winds blowing away from the National Weather Service Doppler Radar located in nearby Pleasant Hill, while cool colors (greens) show winds blowing toward the radar. As a basic explanation, where intense red and green colors are located next to each other, rotation can be inferred.
Multi-layer Panel Display of Base Reflectivity
Multi-layer Panel Display of Base Velocity