Large Hail in Southeast Michigan on April 9, 2001
On April 9, numerous thunderstorms moved through southeast Michigan in the morning. Despite chilly surface temperatures from around 40 through the mid 40s, the atmosphere from about 3000 feet aloft was unstable. The primary severe weather threat was hail, and several severe thunderstorm warnings were issued when thunderstorms on the National Weather Service Doppler Radar indicated storms capable of producing hail 3/4-inch in diameter, roughly dime-size, or larger.
Visible satellite images, taken from satellites approximately 22,000 miles above the earth's surface, take photographs of the clouds. Unlike infrared satellite images, which sample the cloud temperature and are useful both day and night, visible images are only useful during daylight hours, when the satellites can "see" the clouds courtesy of the sunlight shining off of the clouds. All types of satellite images help meteorologists forecast the weather, by understanding where storms are moving and how clouds are developing or dissipating.
|An early morning visible satellite image, taken at 1345Z or 945 AM, shows well-developed
clouds over south-central lower Michigan. A pair of very bright, textured clouds are located just
north of the Michigan/Ohio border. The brightness of these clouds represent well-developed
clouds, or clouds extending to high altitude. On a visible image, the higher the cloud top, the
brighter the cloud will appear due to the sun shining on them at high altitudes.
Just after this satellite photograph, at 1347Z or 947 AM, National Weather Service meteorologists, constantly monitoring National Weather Service Doppler Radar, were following two thunderstorms over far western Lenawee County. These thunderstorms, approaching severe criteria with regard to hail, were moving east-northeast at 50 mph. At 954 AM, the National Weather Service issued a severe thunderstorm warning for both Washtenaw and Lenawee Counties, with the primary threat, as stated in the warning, being large hail.
On this radar image, we are observing "reflectivity", or the intensity of the rain as shown by the National Weather Service Doppler Radar. Gray and blue colors represent light rain, while greens and yellows represent a moderate rainfall. The red colors signify very heavy rain. Numerous other radar images, such as wind velocity and vertically-integrated liquid or VIL, help the forecaster determine the potential severity of the thunderstorm.
The first report of severe hail from these thunderstorms was provided by an individual just north of Adrian at 1005 AM. Half-dollar sized hail was indicated at that time. In Washtenaw County at 1011 AM, law enforcement officials noted hail of golf ball size in Manchester. The thunderstorm over central Lenawee County would continue to be severe, producing hail to dime size in northwest Monroe County at 1025 AM.
The severe thunderstorm over Washtenaw County continued to provide for numerous reports of large hail. Golf ball-sized hail was indicated in Saline at 1027 AM and in Ann Arbor at 1030 AM. As the severe storm moved into Wayne County, hail was reported to be two inches in diameter in Belleville, or slightly larger than a golf ball.
Courtesy of a Skywarn spotter and amateur radio operator from Wayne County, a photograph of large hail was taken. Hail of this size can damage property, and even cause injury to someone who may be struck by it. The National Weather Service recommends that individuals remain in sturdy shelter, away from windows and exterior walls, when a severe thunderstorm warning has been issued to help avoid the dangers of large hail and strong winds.