June 5, 2010 Tornadoes

 

 Early on June 5^th morning thunderstorms tracked across Iowa and into Illinois, leaving behind extensive cloud cover that was slow to dissipate during the day. Farther west a weak area of low pressure was centered across western Iowa, with a trailing cold front over the Missouri Valley. It was anticipated that breaks in the cloud cover would lead to thunderstorms development along the cold front and near the warm front/low pressure intersection (triple point). By the afternoon thunderstorms had developed, and a strongly sheared atmosphere was leading to updraft rotation, and even a few brief tornadoes in central Iowa. Despite pockets of sunshine and temperatures rising into the lower 80s, the storms along the cold front failed to intensify quickly, with weak rotation and surface wind gusts below 40mph.

By late afternoon as the cold front was just entering east central Iowa, showers began to develop over southeast Iowa. These showers were located in a very favorable environment, with moderate instability and high shear. Originally, they appeared to be forced by frontogenesis near the edge of the deepest 850mb moisture. As a result, at the onset they took on an elevated appearance on radar, but as they continued east it was clear they were tapping surface air. As further evidence, the showers passed over the Quad Cities National Weather Service office, where on duty meteorologists were able to verify the low cloud bases. Soon after crossing the Mississippi River, these showers began to develop into mini, or low topped supercells. They began to weakly rotate, and took on the familiar “hook echo” radar presentation, but cloud tops were only around 25,000ft. So with very little ice in the clouds, lightning was initially not that common.

The evening weather balloon soundings from Davenport, Iowa and Lincoln, Illinois revealed weak capping, keeping a lid on thunderstorm development. However, large scale forcing arriving in the form of a mid level shortwave trough and 70kt jet streak embedded in the flow quickly eroded the cap. On a line from Warren to Henry County, Illinois the showers underwent rapid intensification into thunderstorms. To the south and east lay a moderately unstable and highly sheared environment in central Illinois.

One of the thunderstorms quickly developed a wall cloud near the Warren and Knox County border, and would go on to produce its first tornado south of Galesburg, near Abingdon (outside of the Quad Cities service area). This thunderstorm would continue to produce tornadoes that would damage Yates City, Elmwood and dissipate near Peoria. Shortly after, around 730pm, a thunderstorm began to rapidly intensify south of Kewanee, Illinois. The storm was displaying strong rotation, and a tornado warning was issued at 729pm. Soon after, residents of southeastern Henry County could see a blocky, weakly rotating wall cloud. Just 5 minutes later another storm to the north began to show rapid rotation, and a second tornado warning was issued at 734pm for central Bureau County. This storm resulted in numerous wall cloud reports to the southwest of Princeton. This storm would go on to produce a brief, weak tornado in central LaSalle County. Meanwhile, the southern storm continued into far northern Stark County, on an east southeast path. The strongest part of the storm rode the Bureau/Marshall County border, as the wall cloud began to lower and spin faster as it approached the town of Henry, Illinois.

Farther northwest, along the cold front near the triple point, a persistent thunderstorm was approaching Maquoketa, Iowa. As it neared the northern edge of town it quickly spun up, showing signs of a tornadic circulation on radar for the first time. A third tornado warning was issued at 743pm, and shortly after, reports came in of tornado damage in Maquoketa.  The interesting part about this storm is that it did not show the precursors to tornado development that the storms farther southeast did. Instead, the tornadic circulation showed up on radar after the tornado was already on the ground. This tornado touched down at approximately 740pm, and was on the ground for 2 ¼ miles. Tracking through the northern parts of town, the damage path was about 150 yards wide, and the majority of the damage was to trees, with many mobile homes and vehicles being damaged from falling limbs. A farmstead also lost its front porch and had several outbuildings damaged, while the elementary had its sign destroyed and a rooftop air conditioning unit moved. Based off this damage, a NWS storm survey team rated the tornado an EF1, with maximum wind speeds around 105mph. About 20 minutes later, the circulation intensified yet again, and another tornado touched down north of Goose Lake, Iowa. About 100 yards wide, and a ½ mile long, this tornado was rated an EF0 with winds of around 75mph due to tree damage in the area. 

 

 

Above: Reflectivity and storm relative motion of the storm that produced the tornado in Maquoketa. Top images are before the tornado developed, bottom are when it was already on the ground.

   

  

 

Above: NWS storm survey pictures from north side of Maquoketa

Above: Enhanced visible satellite shortly after 700pm showing overshooting tops on three tornado warned storms.

Back in extreme northern Marshall County, Illinois the thunderstorm was showing violent rotation in the lower levels on radar. At this time the tornado warning was updated to include warning of “significant structural damage” possible with this tornado. Also, by 807pm second tornado warning for this storm had been issued (the 4^th of the day), because the original was nearing expiration. As the circulation passed into Putnam County at 810pm, a tornado finally touched down near the eastern shore of Sawmill Lake.

 

Above: Radar imagery around the time of the first tornado touchdown, as the storm is just entering extreme southeast Putnam County

Significant tree damage occurred along Route 26, with trunks snapped and limbs scattered in all directions. The tornado continued east, towards Taylor Road, continuing shred trees and damage houses with falling limbs. Around this time a horse trailer was destroyed and parts of it carried over 300 yards. Adjacent to this damage, a field showed signs of scouring from the tornadic winds. Farther down Taylor Road a farmstead received significant damage when the tornado took half of the roof off a metal outbuilding, and totally flattened the barn. Fields nearby continued to show signs of scour, and a multivortex structure. Sheet metal and other debris was evident hundreds of yards out into fields in all directions. About ¼ mile up the road was a 400ft tall cell phone communication tower. The tornado was able to reduce the tower to nothing but twisted metal, and flattened the chain link fencing surrounding the anchor supports. Shortly before this time, a local resident snapped a photograph of a wedge tornado to her northwest from south of Route 18, near Stage Coach Road.

The tornado continued just north of Route 18, with continued destruction of farm outbuildings, grain bins and trees. Here debris was lofted hundreds of yards into adjacent fields, boards driven over a foot into the ground, and corn stalks were sheared off at the base and scattered to the east. The tornado then passed near the intersection of Routes 89 and 18, and entered into Magnolia.

 

Above: Radar imagery from near the time the tornado entered Magnolia

Significant damage occurred on the north side of town, as four homes lost all of parts of their roof. A trailer was also destroyed when the tornado rolled it over multiple times and into a grove of trees to the south. Scattered across town was damage to trees and outbuildings and damage done by flying debris. At the eastern edge of town, the former school gymnasium collapsed, and the roof was carried 200 yards out into a nearby field. This tornado continued east before it was determined to have lifted about 1 ¼ miles into LaSalle County at 835pm, thanks to coordination with the weather service office in Chicago. A NWS storm survey team was able to determine this tornado was on the ground for 9 ½ miles, with a maximum width of around ½ mile. It was rated an EF2 on the Enhanced Fujita scale, with maximum winds of 135mph when it toppled the cell phone tower. Within the town of Magnolia the tornado was beginning to weaken, though wind speeds were still estimated to be between 120 and 130mph.

 

  

  

  

  

 

Above: NWS storm survey pictures from Putnam County

The parent supercell thunderstorm would then go on to produce multiple tornadoes all the way into Indiana, including the EF3 between Streator and Dwight, Illinois. The outbreak would continue through the evening and overnight, spreading in size to include Indiana, Michigan, Ohio and Ontario, in addition to Iowa and Illinois, with over 30 reported tornadoes.