forecast vs prognosticate

forecast is a noun but prognosticate is not a noun.

Word	Noun	Adjective	Verb	Adverb
forecast	Yes	No	Yes	No
prognosticate	No	No	Yes	No

As verbs, prognosticate is a hypernym of forecast; that is, prognosticate is a word with a broader meaning than forecast:

Other hypernyms of forecast include anticipate, call, forebode, foretell, predict, promise.

As verbs, forecast and prognosticate are synonyms defined as:

Other synonyms of forecast include augur, auspicate, betoken, bode, foreshadow, foretell, omen, portend, predict, prefigure, presage.

forecast (noun)	prognosticate (noun)
a prediction about how something (as the weather) will develop

forecast (verb)	prognosticate (verb)
judge to be probable	make a prediction about; tell in advance
predict in advance	indicate, as with a sign or an omen
indicate, as with a sign or an omen