Thunderstorms and Squalls
Thunderstorms mau be generated along active cold fronts or
over land on still, hot summer days. In both cases, strong
convection currents are set up, and build large cumulonimbus
clouds.
Raindrops in these large clouds grow so big that they
disintegrate. This creates a charge of static electricity -
which is eventually discharged to produce lightning and
thunder.
Lightning is attracted to high points (such as a yacht's
mast), but is usually discharged quickly and safely through
the mast and rigging to the sea. Very strong and rapidly
shifting winds can be expected just in front of a
thundercloud, as the cloud effectively 'sucks' air in from
around it. Squalls generally pose a greater threat to small
craft than the risk of lightning.
Line squalls
Line squalls may occur along the line of very active cold
fronts, particularly if there is a marked kink in the
isobars (i.e. shift in wind direction) along the line of the
front. They are marked by a clearly-defined black 'roll
cloud' , similar to that at the leading edge of a
thunderstorm. The effect is similar: strong gusts of wind
followed by heavy rain, but in extreme cases the turbulence
may be enough to trigger waterspouts or tormadoes,
representing a real danger to small craft that is best
avoided by aiming to pass under the lightest part of the
approaching roll cloud.
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