There were lots of indicators of a German attack. Most notably, German railroad Enigma. The Wehrmacht (for once) maintained good operational and communications security prior to the Bulge, put even without ULTRA, there were indications that the Germans were up to something.
The First Army G2, Colonel Benjamin “Monk” Dickson was warning of a German offensive before Christmas, and on December 14, stated unambiguously, “It’s the Ardennes!”. He was sent to Paris to rest.
Eisenhower’s G2, Kenneth W. Strong, also believed that the Germans were likely to make a final gamble, most likely in the Ardennes or the area around Achen. Strong was sent to brief Bradley (who dismissed his warning) and Patton, who took it half seriously.
LOL! The Army hasn't changed . . . SNAFU!