Was traveling towards Wisconsin from Iowa on the interstate in the outside lane. Traffic was very light. Near the border, the interstate went over a hill which had been cutdown to reduce the grade of the freeway. The cut was about sixty feet below the top of the hill. The weather was very stormy with very low clouds and wind but no rain. As soon as I exited the cut through the hill, a strong gust of high crosswind hit my truck and fifth wheel, and I was suddenly on the shoulder of the freeway. Fortunately, I was on high alert due to the weather, and took my foot off the gas and then gently moved back over into the traffic lane. Had this been a two lane road with no shoulder or had I been in the inside lane with heavy traffic, the outcome might have been seriously different!