Suitable for use only during fair weather / (of friends, etc.) Dependable only in the absence of trouble.

(meteorology) a balloon that carries meteorological instruments aloft in order to measure, record and return data concerning atmospheric pressure, temperature and humidity

Not affected by climatic conditions; capable of normal operation regardless of precipitation, wind, sun, etc. / (figuratively) Always there when needed, reliable, dependable, loyal, faithful.

Used to inquire about the weather. / (by extension, idiomatic) Indicating a change of subject to unimportant topics.

(Britain) Undesirable weather, especially foggy or stormy weather conditions.

Beaten or harassed by the weather; worn or damaged by exposure to the weather or the outdoors, especially to severe weather.

(idiomatic) To reach the end of a very difficult situation without too much harm or damage.

(nautical) A ship's deck which has no overhead protection, which is open to the weather; a ship's uppermost deck.

(meteorology) Any phenomena related to the radiation and particles emitted by the Sun, especially in the vicinity of the Earth that may have an effect on the Earth or human activity in the space.

An ability to predict short-term weather. / (by extension) An ability to detect undercurrents and subtleties in a situation. / A device for monitoring the weather.