14. adjectives (3) position after 'as', 'how', 'so', 'too'
After 'as', 'how', 'so', 'too' and 'this/that' meaning 'so', adjectives go before a/an. This structure is common in a formal style.
I have as good a voice as you.
How good a pianist is he?
I could not afford that big a car.
It was so warm a day that I could hardly work.
She is too polite a person to refuse.