天気予報はまったく当てにならない。

weather; the elements; fair weather; fine weather

forecast; prediction

topic marker particle; indicates contrast with another option (stated or unstated); adds emphasis

really; truly; entirely; completely; wholly; perfectly; indeed; good grief (expression of exasperation)

aim; object; purpose; end; expectations; prospects; hopes; something that can be relied upon; snack served with alcoholic drink; pad; guard; blow; strike; addressed to; per

at (place, time); in; on; during; to (direction, state); toward; into; for (purpose); because of (reason); for; with; by; from; as (i.e. in the role of); per; in; for; a (e.g. "once a month"); and; in addition to; if; although

to become; to get; to grow; to be; to reach; to attain; to result in; to prove to be; to consist of; to be composed of; to succeed; to be complete; to change into; to be exchanged for; to play a role; to be promoted; to do ...