Typical cloud formations of a warm front

A rapid decrease in air pressure ('falling barometer') invariably signals
the approach of bad weather. If the direction of the wind at the same time
is shifting in a clockwise direction (e.g. from east to south), this means
that a low-pressure zone is approaching. This may be corroborated by
the appearance of the typical cloud formations: cirrus (Ci), cirrostratus
(Cs), altostratus (As). Rainfall is imminent at this point. Nimbostratus
(Ns) is frequently associated with strong rains. An extremely fast drop in
air pressure signals the approach of a storm.