Wherefore art thou, Words?

Why is it that when I have the time to write, the words just won't come? Most days, as the kids are screaming and fighting and calling for Mommy, it's all I can do to shut off my writer's brain and switch it over to Mommy mode. But this morning, while my husband is at work and the kids are still tucked into their beds, a time when I should be able to create, the words are staying stubbornly lodged in my brain. I despise this feeling of knowing what I want to write but being unable to write it. But it's still early, and I'm hoping the day will get better.