Weather Archive

Friday, January 1, 2010

Hail Size Increased In Severe Storm Warnings

When you think of what makes thunderstorms severe, most people assume lightning is a factor.  But it is not part of the criterion for issuing severe warnings.  The National Weather Service (NWS) is responsible for issuing severe thunderstorm warnings when winds reach 58 mph or  higher.  But hail is also part of the factor.  It used to be when hail reached 3/4 of an inch a storm became severe.  But the now the  threashold is 1."

The one inch criterion had been use in hail country of the southern plains and over  the western United States. Hail is common in these locations due to lower freezing levels in the atmosphere and stronger vertical updrafts.  Updrafts result in the formation of hail when water droplets freeze and get carried upward until the they freeze and fall back down.  The cycle repetes until the hail grows too large for the updraft to keep it suspended in the air.

This is a good idea because it reduces the perception of over warning saturation during our busy summer storms season. Warnings are often issued for penny sized or 3/4" hail.  It is rare for 1" golf ball sized hail to occur in our area. Now thunderstom warnings carry more weight and hopefully people will take them seriously when storms hit.

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