forecast vs portend

forecast is a noun but portend is not a noun.

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

As verbs, forecast and portend are synonyms defined as:

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

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

forecast (verb)	portend (verb)
judge to be probable	indicate, as with a sign or an omen
predict in advance
indicate, as with a sign or an omen