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Dirty Hail
11/11/2002
Listen in RealAudio 
Hi, I'm Bryan Yeaton for The Weather Notebook. For her master's thesis, our staff
meteorologist on Mount Washington, Nicole Plette, used a numerical model to study a hailstorm
that occurred in Canada's Northwest Territories in May of 1999.
NP: This hailstorm happened in very high latitudes and that's a very rare occurrence; most
hailstorms happen in lower latitudes where there's a lot more moisture and the temperature is
a lot warmer. When I first set out to do this study I was basically just trying to study what
started this hailstorm, but what I eventually found out was that the model wasn't able to
capture that storm unless we changed the soil type that the model was using.
The soil type?
NP: Well, soil types have many different kind of diffusivities of thermal properties and of
moisture content and the heat and moisture are very, very important to the formation of
hailstorms and what I originally found was that the model had made the assumption that all the
soil type in North America was just one soil type and it was sort of a clay. Hailstorms are
very dependent upon moisture content and heat and the more moisture available, the more heat
there will be because as the water condenses it releases latent heat which adds to the energy
of the storm.
So, how does what you found help us in future hailstorms?
NP: What we've been able to do now... the Canadian Meteorological Center actually has
implemented a whole new soil type scheme for the model which includes 38 different types of
ground cover including different types of vegetation, different moisture contents and
different soil types, and that will be able to help us forecast hailstorms much more
accurately.
Who'd have thought dirt was so important. The Weather Notebook is supported by Subaru of
America and The National Science Foundation.
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