Brief stroke symptoms precede sever strokes only 1 in 8 times.  Transient ischemic attacks--TIAs--are a warning for the real thing, but seven of eight strokes occur without warning symptoms.
D006801:Humans; D002546:Ischemic Attack, Transient / Q000175:diagnosis*; D018570:Risk Assessment; D020521:Stroke / Q000175:diagnosis*