"It is chilly today."

Translation: Сегодня прохладно.

[ArhiMith]

Сегодня холодно, а не прохладно, люди :)

[deactivated user]

Смотря где. :D

[mph.vgc]

Да Arhi, опять пьяные китайцы вмешались в процесс обучения. "Chilly" - никак не прохладно, а "холодно"! "Прохладно" ближе к "cool"

[frazer_124]

Why doesn't холодно work here..?

[Ishana92]

It is not the same thing (althought one could argue that it is not such big of a difference). Cold vs chilly

[saxmund]

I suspect Russians would say прохладно when most of us would say холодно

[Gulpepper]

Is this like красный and прекрасный?

[Shady_arc]

Not quite, though the word indeed uses a prefix. It is про + хладный (an obsolete version of холодный).

Some words came from Church Slavonic and entered Russian. Such vowel changes should not suprise you. The following words are essentially descendants of the same word: one has East Slavic origin, anothe Church Slavonic one:

• голова "head" / глава "chapter"
• город "city" / -град (mostly used as a component of some toponyms)
• молодой "young" / младший "younger" (e.g., in "little brother")
• порох "powder" / прах "ashes, remains (of a person)"
• голос "voice" / гласный "vowel"
• сторож "guard, watchman" / страж "guardian"

[BrunnoHC]

Yes, it is...

[Jay239607]

Why "сегодня есть прохладно" is not correct?

[dfggh4]

Because прохладно is an adverb. Есть doesn't work like "to be".
You also say мне холодно for "i am cold".

[Jay239607]

I should know it by now. Thanks