What does a hail shaft look like?

Ever wonder what hail looks like, from a distance, coming out of the base of a thunderstorm?  Below is a picture taken by a citizen from Mt. Horeb in Dane County, looking east-southeast at a hail shaft - the white-colored streak between the cloud base and the tan-colored building. You can also see a small rainbow just above the ground level on the left side of the hail shaft.

Dane County hail shaft

A hail shaft is a precipitation-filled downdraft containing large amounts of hail, as indicated by the whiteness of the precipitation curtain, relative to the surroundings. Hail forms in stronger  thunderstorm clouds, particularly those with at least moderately intense updrafts, high liquid water content, appreciable  vertical extent, large water droplets; and where a good portion of the cloud layer has a temperature below freezing 0 °C (32 °F).  Hail-producing clouds are often identifiable by their green coloration.

During the afternoon hours of Thursday, July 23, 2009, scattered clusters of thunderstorms pulsed up and down across South-central and Southeast Wisconsin.  Their movement was to the south-southeast.  Many of them dumped brief heavy rains and small hail one-half inch in diameter or less, and gusty winds of 30 to 40 mph.  The storm in the picture above was one of them.  Some of the storms on July 23rd did produce hail up to 1 inch in diameter.

On occasions, thunderstorms in Wisconsin do produce large hail stones 1 inch in diameter or larger.  When this happens, the Milwaukee/Sullivan National Weather Service Office will issue Severe Thunderstorm Warnings for such storms.  Additionally, if the storm is capable of generating damaging downburst winds of 58 mph or higher, a Severe Thunderstorm Warning will be issued, even if there isn't any hail.

The largest hailstone in Wisconsin's recorded history was 5.7 inches in diameter.  It was produced by a severe thunderstorm during the evening of May 22, 1921 on the north side of Wausau.  The 2nd largest hailstone in Wisconsin was 5.5 inches in diameter, assocated with a Port Edwards supercell thunderstorm on June 7, 2007.  The 3rd largest hailstone, 5 inches in diameter, was generated by a thunderstorm 2 miles east-northeast of Delafield on June 7, 2008.

The worst day for hail occurred on April 13, 2006, when three supercell thunderstorms moved east across southern Wisconsin.  In their wake, they left at least $420 Million in damage to home siding, windows, and roofing, not to mention what happened to vehicle windows and bodies.  The lion's share of the hail damage was related to the supercell that moved through Iowa County through the Madison area all the way to northern Milwaukee County.  To read the storm write-up for April 13, 2006, please click here here.

Most of Wisconsin's hailstorms occur in the months of May, June, and July.  For limited statistical information about hail storms and other forms of severe winter and summer weather over Wisconsin, please click here.  For information on the initiation hour of hailstorms in Wisconsin, including other severe weather events, click here.

For some background information on hail, please click here, or  here.  This information was generated by the National Severe Storms Laboratory in Norman, OK.

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