A frontal boundary meandering about Southern Iowa and Central Illinois lifted into Central Iowa and North Central Illinois by afternoon.  A nearly stacked low center over the Mid Missouri River Valley underwent filling as it shifted eastward across Southern Iowa and Central Illinois.  Much of Northern Illinois along and north of Interstate 88 was thrusted into the warm sector where temperatures climbed into the upper 70s to lower 80s.  Meanwhile, areas north of the boundary were quite cool with a brisk northeast surface wind and plenty of cloud cover keeping temperatures down in the 60s.  12z soundings from KILX and KDVN indicated very steep lapse rates with Cape values of 2000-3000 J-kg.  Thunderstorms quickly erupted along the boundary from Central Iowa through Northeast Iowa into Northern Illinois by late morning, and continued through the afternoon.  The storms produced large hail, heavy rain, damaging winds and several tornadoes over portions of Northwest Illinois.  Thunderstorm interaction with the frontal boundary was believed to be the culprit for spawning 6 weak and short lived tornadoes across Henry and Bureau Counties.  The only damage occurring with the tornadoes was in Manlius and Neponset where large trees and signs were blown down.  High winds, associated with a possible gustnado, blew down the back wall and knocked out several windows of an abandoned grocery store in Cambridge.  The glass and bricks were hurled to the ground, causing damage to a truck parked on one side of the building.  The high winds also downed several trees and power lines.  Power was knocked out to Cambridge and surrounding areas for almost 4 hours.

Tornado in BUREAU, ILLINOIS
From 18-MAY-00 15:00:00 to 18-MAY-00 15:00:00 (CST)
Location: NEPONSET
Tornado F-scale: F0
Property damage: 10K
Reported by: EMERGENCY MANAGER

Tornado in HENRY, ILLINOIS
From 18-MAY-00 14:09:00 to 18-MAY-00 14:09:00 (CST)
Location: GENESEO
Tornado F-scale: F0
Reported by: AMATEUR RADIO

Thunderstorm Wind in BUREAU, ILLINOIS
From 18-MAY-00 14:30:00 to 18-MAY-00 14:30:00 (CST)
Location: PRINCETON
Property damage: 30K
Reported by: NEWSPAPER

Hail in WHITESIDE, ILLINOIS
From 18-MAY-00 11:55:00 to 18-MAY-00 11:55:00 (CST)
Location: MORRISON
Magnitude: 0.75 
Reported by: LAW ENFORCEMENT

Hail in BUREAU, ILLINOIS
From 18-MAY-00 14:25:00 to 18-MAY-00 14:25:00 (CST)
Location: WALNUT
Magnitude: 1.00 
Crop damage: 5K
Reported by: NEWSPAPER

Hail in ROCK ISLAND, ILLINOIS
From 18-MAY-00 13:35:00 to 18-MAY-00 13:35:00 (CST)
Location: ROCK IS
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Tornado in HENRY, ILLINOIS
From 18-MAY-00 14:11:00 to 18-MAY-00 14:11:00 (CST)
Location: WOODHULL
Tornado F-scale: F0
Reported by: LAW ENFORCEMENT

Hail in WHITESIDE, ILLINOIS
From 18-MAY-00 14:30:00 to 18-MAY-00 14:30:00 (CST)
Location: PROPHETSTOWN
Magnitude: 0.75 
Reported by: NEWSPAPER

Hail in WHITESIDE, ILLINOIS
From 18-MAY-00 11:27:00 to 18-MAY-00 11:27:00 (CST)
Location: ROCK FALLS
Magnitude: 0.75 
Reported by: FIRE DEPT/RESCUE SQUAD

Thunderstorm Wind in HENRY, ILLINOIS
From 18-MAY-00 14:09:00 to 18-MAY-00 14:09:00 (CST)
Location: CAMBRIDGE
Property damage: 50K
Reported by: LAW ENFORCEMENT

Hail in WHITESIDE, ILLINOIS
From 18-MAY-00 14:35:00 to 18-MAY-00 14:35:00 (CST)
Location: TAMPICO
Magnitude: 0.75 
Reported by: NEWSPAPER

Hail in WHITESIDE, ILLINOIS
From 18-MAY-00 12:05:00 to 18-MAY-00 12:05:00 (CST)
Location: STERLING
Magnitude: 0.88 
Reported by: LAW ENFORCEMENT

Hail in ROCK ISLAND, ILLINOIS
From 18-MAY-00 13:58:00 to 18-MAY-00 13:58:00 (CST)
Location: COAL VLY
Magnitude: 0.75 
Reported by: TRAINED SPOTTER

Tornado in HENRY, ILLINOIS
From 18-MAY-00 14:34:00 to 18-MAY-00 14:34:00 (CST)
Location: GALVA
Tornado F-scale: F0
Reported by: LAW ENFORCEMENT

Tornado in HENRY, ILLINOIS
From 18-MAY-00 13:50:00 to 18-MAY-00 13:50:00 (CST)
Location: ORION
Tornado F-scale: F0
Reported by: LAW ENFORCEMENT

Tornado in BUREAU, ILLINOIS
From 18-MAY-00 14:50:00 to 18-MAY-00 14:50:00 (CST)
Location: MANLIUS
Tornado F-scale: F0
Property damage: 15K
Reported by: EMERGENCY MANAGER

Thunderstorm Wind in ROCK ISLAND, ILLINOIS
From 18-MAY-00 14:00:00 to 18-MAY-00 14:00:00 (CST)
Location: SILVIS
Magnitude: 52 E
Property damage: 2K
Reported by: LAW ENFORCEMENT