Cold Startup Process

I know that on cold startup the car should rev up to 3000rpm and then come down. It has always done that until recently. Here in Ohio the weather has gotten much colder. I have noticed since the temps dropped below 50 that when i go out in the morning and start it up, it doesn't rev up like it did before. It only revs up to 1500-1800 rpm. Now a couple time i took it out when the temps got a little warmer again and it revved like normal on startup. Is this normal when temps get colder or is there something i need to check?

Thanks
Kerry