Old English weder "air, sky; breeze, storm, tempest," from Proto-Germanic *wedra- "wind, weather" (source also of Old Saxon wedar, Old Norse veðr, Old Frisian, Middle Dutch, Dutch weder, Old High German wetar, German Wetter "storm, wind, weather"), traditionally said to be from PIE *we-dhro-, "weather" (source also of Lithuanian vėtra "storm," Old Church Slavonic vedro "good weather"), suffixed form of root *we- "to blow." But Boutkan finds this "problematic from a formal point of view" and finds only the Slavic word a likely cognate.
Greek had words for "good weather" (aithria, eudia) and words for "storm" and "winter," but no generic word for "weather" until kairos (literally "time") began to be used as such in Byzantine times. Latin tempestas "weather" (see tempest) also originally meant "time;" and words for "time" also came to mean weather in Irish (aimsir), Serbo-Croatian (vrijeme), Polish (czas), etc. Weather-report is from 1863. Weather-breeder "fine, serene day which precedes and seems to prepare a storm" is from 1650s.
Surnames Fairweather, Merriweather probably reflect disposition; medieval lists and rolls also include Foulweder, Wetweder, Strangweder.
Old English eall "every, entire, the whole quantity of" (adj.), "fully, wholly, entirely" (adv.), from Proto-Germanic *alnaz (source also of Old Frisian, Old High German al; German all, alle; Old Norse allr; Gothic alls), with no certain connection outside Germanic. As a noun, in Old English, "all that is, everything."
Combinations with all meaning "wholly, without limit" were common in Old English (such as eall-halig "all-holy," eall-mihtig "all-mighty") and the method continued to form new compound words throughout the history of English. Middle English had al-wher "wherever; whenever" (early 14c.); al-soon "as soon as possible," al-what (c. 1300) "all sorts of things, whatever."
Of the common modern phrases with it, at all "in any way" is from mid-14c., and all "and everything (else)" is from 1530s, all but "everything short of" is from 1590s. First record of all out "to one's full powers" is 1880. All clear as a signal of "no danger" is recorded from 1902. All right, indicative of assent or approval, is attested by 1837; the meaning "satisfactory, acceptable" is by 1939, from the notion of "turning out well."
The use of a, a' as an abbreviation of all (as in Burns' "A Man's a Man for A' that") is a modern Scottishism but has history in English to 13c.
1829, U.S. slang, said to be a euphemism for hell-fired, but perhaps it is what it says, with all as an intensive.