Vetus Meteoliner Anleitung Seite 41

9-5 The hazardous 'trough'
To begin with, everything happens as the weather forecast has
predicted - a cold front draws near, the air pressure drops
smoothly, and then the pressure drop moves info reverse and
starts climbing - as expecied - as the front passes over. Then it
happens: instead of the pressure increasing steadily and thereby
announcing fair weather in the rear of the cold front, it only
increases 'to plan' for a few hours, before starting to rise much
more slowly. This is the alarm signal for an imminent 'trough'!
In the next phase, the pressure even stops rising altogether, and
this is our last chance to escape the gale that is heading our way
- i.e. for the traugh - for in 1 - 3 hours' time we shall be right in the
thick of it.
In the middle of the trough, the air pressure will even drop a few
hPa. Later on, however, when it starts shooting up again, the
worst will still not be over, as the northwesterly gale will keep rag-
ing until the pressure stops rising - and this generally takes 20
hours or so.
Baroscope
Date
Cold front
Time scale (past 24 hours)
Troughs are often not recognized soon enough by the meteoro-
logical offices, and the warnings are only given once one is well
out to sea. If you have a baroscope and refer to it frequently, you
need never be taken by surprise and - with a bit of luck - will be
able to keep out of harm's way.
ENGLISH
Pressure
Time
in hPa
Trough
10.0801
41