2001 LS 2 door brake problem.
 

2001 Chevrolet Blazer LS. Nothing done to suspension only modification is a cold air intake. it just snowed where i live and now the roads are back to normal and when i approach a red light, no problem brake feels good, but if the redlight is a minute or two long, the brake pedal keeps going down and down until it touches the floor, if i keep it at about 25% it will start to roll then i need to continue pressing harder and harder to keep it from rolling forward. Do i have air in my brake lines, or is the master cylinder going bad? has this problem happened to anyone else? thank you!

Sounds like you got a bad line somewhere. Brake fade is usually a tell tail sign.

finger in the wind.. 95% chance of bad master cylinder. Mainly because your brakes still work.
But first thing to do if that ever happens is to check fluid. If you arent losing brake fluid, you have no leak. If you are, it may be a cracked line or leaking brake cylinder
Actually the term 'brake fade' means loss of braking power due to pads or shoe surface overheating.

Sorry for the wrong term use. Should have said pedal fade.

yeap i've been checking for about a week and no change in brake fluid level. I'm just going to have to spring for a new master cylinder because this isn't a subject i'd want to tinker around with. The pedal always comes back up after i let off and the fluid is not leaking out of a line. Thanks for the back-up advice guys always a pleasure to read the endless free knowledge on the website!