The invasion planners specified a set of conditions regarding the timing of the invasion, deeming only a few days in each month suitable. A full moon was desirable, as it would provide illumination for aircraft pilots and have the highest tides. The Allies wanted to schedule the landings for shortly before dawn, midway between low and high tide, with the tide coming in. This would improve the visibility of obstacles the enemy had placed on the beach while minimising the amount of time the men had to spend exposed in the open. Specific criteria were also set for wind speed, visibility, and cloud cover. Eisenhower had tentatively selected 5 June as the date for the assault. However, on 4 June, conditions were clearly unsuitable for a landing; high winds and heavy seas made it impossible to launch landing craft, and low clouds would prevent aircraft from finding their targets.