Great Blue Norther of November 11, 1911
On Saturday, November 11, 1911, a cold snap, known as the Great Blue Norther or 11/11/11, affected the Central United States. Many cities broke record highs, going into the 70s and 80s early that afternoon.
Source: Wikipedia — Great Blue Norther of November 11, 1911 (CC BY-SA 4.0)