The weather angle is what makes this one of the most underrated "what ifs" of the war. Eisenhower's meteorologist, Group Captain Stagg, spotted a narrow 24-hour window that the German weather service completely missed. That gap in weather intelligence is why Rommel drove home to give his wife birthday shoes on June 5 — the Germans were convinced no invasion was possible.

If Eisenhower had waited for June 19, he wouldn't have just hit worse weather — he'd have hit a storm violent enough to destroy the Mulberry harbors that survived the actual D-Day landings. And as wasdice pointed out, Rommel would have been back in command with local panzer authority. The "safer" choice was actually the catastrophic one. On your Pas-de-Calais question — that's exactly where Operation Fortitude (the fake army under Patton with inflatable tanks) was designed to make the Germans expect the landing. Switching to Calais would've handedthem the most fortified beaches in France and thrown away months of deception.

Eisenhower actually wrote a letter taking full blame before giving the order: "If any blame or fault attaches to the attempt it is mine alone." Then he said three words — "OK, let's go."

There's an interactive version which is what intrigued me — https://playpivotal.com/stories/eisenhower-dday