Used to indicate that something will happen in the near future, often with a sense of 'within a short while' or 'in the coming days/weeks'. Common in both spoken and written Japanese.
Let's meet again soon.
It will probably rain before long.
Standard kanji-kana mixed spelling.
Alternate spelling using 内 for うち; less common but seen.
Phrase composed of 近い (chikai, 'near') + うち (uchi, 'within') + に (ni, particle). Literally 'within the near time'.