Lewis & Short

prae-scisco, ĕre, v. inch. a., to find out, or learn beforehand (not in Cic. or Cæs.): animos volgi, Verg. G. 4, 70: exploratam fugam, Col. 9, 9, 4: adversos subitosque motus, Amm. 20, 6, 9.
With rel.-clause, Liv. 27, 35, 5.