The peregrines started the day under clear skies with a few clouds, light winds and temp at 53F around 7AM.  The photo shows the female towards the end of the while incubating the eggs and preening.

So how do birds hatch?

The embryo has breached the membrane, is breathing air with its lungs, and is head up, with its head positioned at the large end of the shell.

• Our embryo  uses its egg tooth, a small temporary structure on the op of its beak, to cut through the shell from inside. The eggshell is thinner and weaker than when it was laid, since the growing embryo absorbed calcium from the shell for its bones. The embryo rubs its egg tooth against the shell, which cuts a small hole.
• As it rubs it rotates its body, slowly cutting a ring around the shell.
• When the cut is complete, the hatchling bird pushes its body against the shell, forcing it apart.  It works itself free of the shell membranes and halves. Voila – a baby bird!

Literature cited:

The Raptor Research Project, Raptor Research Project Blog, Saturday, March 10, 2012                                                                                                                        https://raptorresource.blogspot.com/2012/03/