June 2011 was an active weather month for much of the Midwest. Plenty of warm and humid air flowing north from the Gulf of Mexico interacted with a strong early summer jet stream pattern to produce numerous rounds of strong to severe thunderstorms. Areas from Iowa southeast towards the Ohio Valley saw repeated thunderstorm activity through the month which produced heavy rains, totaling two to three times the normal monthly amounts. Temperatures were near normal for much of the area, though the southern third of the state saw temperatures of two to four degrees above normal.
Major Event Summaries...
Clusters of thunderstorms impacted central and southeast Illinois this weekend. All locations picked up rainfall: however, the amounts varied considerably. One band of heavier rainfall over one inch was noted from northern Knox County southeastward along and just north of I-74 to Champaign County. A second corridor extended from southern Fulton County southward to Winchester and Jacksonville. Yet another band of enhanced rainfall greater than one inch stretched from near Chatham in Sangamon County southeastward to Olney in Richland County.
In addition to the spotty heavy rainfall, a few of the storms produced severe weather. In particular, an intense thunderstorm cell during the evening of June 4th produced golfball-sized hail at Weinberg-King State Park in western Schuyler County, then tracked eastward, downing trees and power lines across parts of Menard, Logan, and Sangamon counties. Meanwhile, a second severe thunderstorm knocked a number of trees down in the Danville area.
Clusters of strong thunderstorms impacted parts of central and southeast Illinois on June 10th. The storms initiated along outflow boundaries left behind by previous convection the night before. One boundary stretching along the I-70 corridor became active by mid-afternoon, triggering numerous showers and thunderstorms. These particular cells remained below severe limits, producing penny to nickel-sized hail along with locally heavy rainfall. The heaviest rain occurred across Effingham and Clay counties where 1 to 3-inch amounts led to minor street flooding. Additional thunderstorms developed across east-central Missouri and southern Iowa by late afternoon, then tracked into west-central Illinois during the evening. The most intense cell moved across Schuyler and far southern Fulton counties. This storm produced very large hail at times, including a report of baseball-sized stones in the town of Augusta in Hancock County. Further east, it dropped golfball-sized hail and knocked a few trees down in western Schuyler County. In addition, it produced impressive rainfall rates...with many locations along its path picking up over an inch of rain in just 30 minutes! Other severe thunderstorms tracked northeastward into Scott County, downing trees and power lines and dropping half dollar-sized hail in Winchester.
Several rounds of showers and thunderstorms brought locally heavy rain, especially to the western half of the area. The first round of convection produced 1-2" rains southwest of a Peoria to Taylorville line by early Tuesday morning, June 14th. Additional storms developed that night, lasting into Wednesday morning, June 15th. Locally heavy rain affected many locations north of I-70. Wind gusts up to 54 mph, and hail up to the size of nickels were reported with this batch of storms. Finally, as a boundary moved through the area Wednesday afternoon, isolated severe storms formed in east central and southeast Illinois and developed a couple brief and weak tornadoes in rural Shelby and Coles counties.
Thunderstorms initiated along an outflow boundary stretching from near Jacksonville east-southeast to Effingham and Lawrenceville during the overnight hours of June 17th. Despite relatively stable conditions at the surface, a 30 to 40 mph low-level jet oriented from Texas northeastward to Missouri provided a supply of warm/moist air aloft. This feed of unstable air helped the storms to continually re-develop over the same locations, producing copious amounts of rain. The heaviest rain fell across Morgan and western Sangamon counties, where several observers measured over 4 inches of rain! Some reports of between 5 and 6 inches were also received. As a result, widespread flooding is occurring from Jacksonville in Morgan County to Loami in western Sangamon County. Other slow-moving storms along the boundary brought torrential rain to parts of Richland and Lawrence counties, where observers reported around 4 inches. Click here for more detailed information on flash flooding with this event.
Strong thunderstorms impacted parts of central and southeast Illinois on June 21st, as a cold front slowly approached from the west. Many of the storms produced damaging wind gusts of 40 to 60 mph as well as locally heavy rainfall. Much of the wind damage was concentrated along and east of I-57, as tree limbs were reported down in a number of communities. Other storms knocked tree branches down and produced localized flash flooding from northern Tazewell County northward through Woodford and Marshall counties. Click here to see Local Storm Reports from this event.
A series of thunderstorm complexes affected central and southeast Illinois from Saturday, June 25, into Monday morning, June 27. These Mesoscale Convective Systems (MCSs) formed on the northern fringe of a hot air dome which extended across the southern and central Plains. On the periphery of this hot and humid airmass, thunderstorms repeatedly formed north of a warm front as mid level disturbances tracked east across the Midwest. A strong low level jet stream coming in from the southwest provided additional warm, moist air to feed the storms.
The first batch of MCS activity affected west-central Illinois on Saturday morning and afternoon. Extremely high rainfall rates (as high as 2 inches per hour) were observed with some of these storms. This led to several instances of flash flooding in Scott county. By Saturday evening the low level jet aided another round of heavy thunderstorms which formed in west central Illinois and tracked into the southeast part of the state after midnight. Isolated reports of hail up to the size of quarters, and wind damage were reported with these storms from the Jacksonville to Springfield areas. As the system progressed southeast, very high rainfall rates produced flash flooding in Clay and Effingham counties.
On Sunday evening the same setup was in place, and the first round of storms tracked across the central part of the state around midnight. Isolated wind damage and hail from penny to golf ball size occurred in Peoria, Tazewell, Logan, and McLean counties. Quickly on the heels of this complex, a large and well organized squall line with widespread damaging winds blasted east from Iowa and Missouri at around 60 mph. This system affected all of central and southeast Illinois between 2 and 5 AM Monday morning. Winds of 40 to 50 mph were common along the leading edge of the storms, with isolated damaging downburst winds in excess of 60 mph. Hail up to the size of nickels occurred with these storms. Again, very high rain fall rates led to another round of flash flooding across parts of the area. Click here to see Local Storm Reports from this event.
Individual June Climate Summaries:
For additional climate information:
Illinois State Climatologist Office: http://www.isws.illinois.edu/atmos/statecli/index.htm