Severe Weather Summary of October 18, 2007
Nationwide severe weather reports from October 18. Click here for specific reports.
A powerful fall storm system affected a large part of the Midwest on October 18. Strong low pressure developed out of a deep upper level trough which moved from the Rockies into the Plains overnight, and was strengthened by mid-level jet stream winds in excess of 100 mph. Surface low pressure developed over the central Plains and quickly deepened to 982 mb and moved northeast into southern Minnesota by early evening.
Round #1 of severe weather struck central and southeast Illinois during the early morning hours as a 60 mph low-level jet stream brought deep moisture and warm air northward into the area. Additionally, a mid-level shortwave moved quickly northeast helping to produce widespread showers and thunderstorms. Intense storms developed just after midnight in west-central Illinois producing strong winds which damaged trees and power lines from Scott county eastward into Sangamon county. These storms weakened as they moved northeast into a more stable airmass. New storms erupted around 4 AM in southeast Illinois and developed quickly to the northeast and intensified over the next couple of hours. Between 4 and 6 AM winds in excess of 60 mph damaged trees and power lines from Effingham eastward through Lawrenceville, and northward through Martinsville, Robinson, and Paris. In addition to the strong winds these storms were very efficient rain producers, with between 2 and 4 inches of rain falling within one to two hours over a large part of southeast and east central Illinois.
The system’s warm front pushed north of the area by the early morning hours, and the "dry slot" moved in from the west, shutting off precipitation and bringing mostly sunny skies by morning. The morning sunshine allowed the atmosphere to destabilize ahead of the approaching cold front to the west. Early afternoon temperatures rose well into the 70s, with dewpoints in the 60s. With a moderate risk of severe storms for the eastern half of the state, a special 18Z weather balloon was launched from the Lincoln office. Data showed very strong low-level lapse rates and sufficient moisture in the lower levels to produce a moderately unstable airmass . Additionally, wind fields were very strong aloft. Surface winds of 25-35 mph increased to 75 mph at mid-levels, and 125 mph at upper levels. While the wind direction did not change much with height, the speed difference created an impressive amount of vertical shear which was sufficient to create supercell thunderstorms. By late afternoon the atmosphere had continued to destabilize as the cold front/dry line plowed in from the west. Thunderstorms erupted around 5 PM between the I-55 and I-57 corridor and moved to the northeast at 40 to 60 mph. Frequent lightning, very heavy downpours, hail, and damaging straight line winds accompanied many of these storms. The activity continued until around 7:30 PM. Many locations along and east of the I-57 corridor sustained damage to trees and power lines.
There were no tornadoes associated with this activity, likely due to a lack of directional wind shear locally. Violent tornadoes did develop later in the evening as these storms pushed into Indiana. Over 4 dozen tornadoes were reported over a 2 day period across the central U.S.
Preliminary reports from eastern Illinois:
PRELIMINARY LOCAL STORM REPORT...SUMMARY
NATIONAL WEATHER SERVICE LINCOLN IL
909 PM CDT THU OCT 18 2007
..TIME... ...EVENT... ...CITY LOCATION... ...LAT.LON...
..DATE... ....MAG.... ..COUNTY LOCATION..ST.. ...SOURCE....
..REMARKS..
0525 PM TSTM WND DMG DECATUR 39.85N 88.93W
10/18/2007 MACON IL TRAINED SPOTTER
TREES DOWN ON LAKE SHORE DRIVE
0526 PM HAIL DECATUR 39.85N 88.93W
10/18/2007 M1.75 INCH MACON IL EMERGENCY MNGR
GOLFBALL SIZED HAIL ON THE EAST SIDE OF LAKE DECATUR
0535 PM TSTM WND DMG 1 W CISCO 40.01N 88.74W
10/18/2007 PIATT IL TRAINED SPOTTER
TREE DAMAGE NEAR THE INTERSECTION OF IL ROUTE 32 AND
48...TRAMPOLIN IN A TREE AND A SEMI TRUCK FLIPPED OVER ON
EASTBOUND I-72
0535 PM HAIL ARGENTA 39.99N 88.82W
10/18/2007 E1.00 INCH MACON IL TRAINED SPOTTER
0551 PM TSTM WND DMG BETHANY 39.64N 88.74W
10/18/2007 MOULTRIE IL LAW ENFORCEMENT
TREES AND POWERLINES DOWN...IN ADDITION FUNNEL CLOUD
OBSERVED
0553 PM HAIL 1 S DE LAND 40.11N 88.64W
10/18/2007 E0.88 INCH PIATT IL TRAINED SPOTTER
0602 PM TSTM WND GST COWDEN 39.25N 88.86W
10/18/2007 M74.00 MPH SHELBY IL MESONET
0619 PM TSTM WND DMG CHAMPAIGN 40.11N 88.26W
10/18/2007 CHAMPAIGN IL BROADCAST MEDIA
TREE BLOWN DOWN ON KIRBY STREET JUST WEST OF THE STADIUM.
FROM WILL TV.
0642 PM TSTM WND DMG MATTOON 39.48N 88.37W
10/18/2007 COLES IL TRAINED SPOTTER
NUMEROUS 5 INCH TREE BRANCHES DOWN AND ONE CAR DAMAGED
FROM TREE BRANCH.
0655 PM TSTM WND DMG OGDEN 40.12N 87.96W
10/18/2007 CHAMPAIGN IL CO-OP OBSERVER
POWERLINES DOWN IN OGDEN...ALSO 6 INCH TREE LIMBS DOWN.
MEASURES 58 MPH WIND GUST
0657 PM TSTM WND GST OGDEN 40.12N 87.96W
10/18/2007 M58.00 MPH CHAMPAIGN IL CO-OP OBSERVER
0701 PM HAIL OAKLAND 39.66N 88.03W
10/18/2007 M1.25 INCH COLES IL EMERGENCY MNGR
0725 PM HAIL 8 S SUMNER 38.60N 87.86W
10/18/2007 M1.75 INCH LAWRENCE IL EMERGENCY MNGR
FROM COUNTY EMA.
0725 PM HAIL 6 S SUMNER 38.63N 87.86W
10/18/2007 M0.88 INCH LAWRENCE IL EMERGENCY MNGR
FROM COUNTY EMA.
0730 PM TSTM WND DMG BRIDGEPORT 38.71N 87.76W
10/18/2007 LAWRENCE IL EMERGENCY MNGR
NUMEROUS TREES AND POWER LINES DOWN FROM BRIDGEPORT TO
THE SOUTHWEST SIDE OF LAWRENCEVILLE. FROM COUNTY EMA.
0829 PM TSTM WND DMG COWDEN 39.25N 88.86W
10/18/2007 SHELBY IL LAW ENFORCEMENT
TOWER AT FIRE DEPARTMENT DOWN. SEVERAL TREES ON VEHICLES.
