Vetus Meteoliner Anleitung Seite 43

9-7 Thunderstorms are drawing near
In summer, thunderstorms frequently occur at cold fronts. In this
case you will not need any special warning - these thunderstorms
come as 'standard', as it were. Heat thunderstorms, which form in
the afternoons along the coast and in the second half of the night
over the open sea, cannot always be detected in sufficient time by
observation of the clouds, either because it is dark or because it
so
misty that the towering banks of storm clouds cannot be seen. A
good 12 hours before a heat thunderstorm breaks, however, the
pressure starts falling, slightly but steadily. This is the first warn-
ing sign on the baroscope.
Even while they are still gathering, the mighty cumulus towering
up into storm clouds produce telltale signs on the baroscope:
Superimposed over the gradual fall in pressure are little pressure
'zig-zags' pointing both up and down. These are prodoced by
pressure waves emanating from the cumulus cloubs round about.
If there is a storm cloud in the immediate vicinity, the 'zig-zags'
traced by the Baroscope become quite dramatic. Within seconds,
the air pressure can soar by as much as 5 hPa, to be followed
almost immediately by the first gusty squalls.
Baroscope
Date
Time scale (past 24 hours)
Only when the pressure drops, and drops as abruptly as it first
rose - only then is the thunderstorm over. Now, with the dramatic
fall in pressure, the cold air breaks forth, bringing rain and hail.
Once the air pressure has gone back to roughly what it was
before the thunderstorm, calmer conditions return. If a gentle
pressure drop continues, however, further thunderstorms can be
expected.
ENGLISH
Pressure
Time
in hPa
10.0801
43