Brad,
When you are in business it is usually either feast or famine.
Here in the north east part of the country, you can basically figure that most detailing businesses are not very busy during the months of January and February. Hey, who wants to get their car detailed with a foot of snow on the ground? Once the weather starts to get a little milder by the beginning of March and the chance of snow, ice and road salt are gone, that is the time when detailing really begins to pick up again.
The demand for detailing here in New Jersey usually remains high until late August, right before schools open again. That bit of a slowdown usually only lasts a few weeks until everything gets back to normal from summer vacations, etc.
By the end of September, the phone starts ringing again and doesn't stop until the holidays in December. The autumn is the time of year when just about everyone wants to protect their car from the upcoming extremes of winter weather. Usually, December is relatively busy, however when the extreme cold weather comes a bit early, that can have an effect on demand at that time of the year.
As you can see, some detailing businesses are affected by seasonal conditions more than others.