As you can see here, the
lower values of Flash Flood
Guidance (FFG) are in the mountains and the higher values
of FFG are in Florida and along the coast. The soil
moisture content on this day was fairly uniform. However
the differences in values are due to the type of soil and
the terrain.
In the mountains the soil is rocky and the terrain has
steep slopes. This is prime territory for a lot of runoff
and thus flash floods. (see Big Thompson Flood)
Along the coast and in Central and South Florida, the
FFG values are high. This due to the sandy soils which
allow rainfall to soak in rather than run off. However in
metropolitan areas, where there is a lot of concrete,
rainfall often runs off and produces localized urban
flooding.
Across the southeast, in between the mountains and the
coast the soils are generally clay.
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