what should the psi be for snow tires during the colder part of winter?

That varies from tire to tire manufacturers and the various tires they offer and the vehicle you're asking about.

Generally, go by the maximum recommendation on the side of the tire and determine how much weight you'll be carrying. If you'll be carrying a car or truck load full, then go with the max.
If not, then drop it down approximately 5 to 10 lbs. (10 to 20 lbs only on high pressure tires around 60 to 80 lbs maximum weight rating) Use common sense, if they recommend 36 lbs max. then don't run it below 26 - 28 lbs.

If these were the original tires when the vehicle was new, then there'll be a sticker on the driver's side door on the "B" pillar or on the edge of the door.

Also keep in mind that tire pressure can vary by as much as 15lbs from summer to winter temperatures.

** ADDED IN A LATER EDIT***
Also, always check the pressure when the tires are cold as in the morning.
Once you drive on them, even just a few blocks to a gas station for example, they heat up from the friction caused by rolling down the road. NEVER let air out of the tires if they read high when you get to a gas station using the gauge on their air pumping station. The high reading you're getting is due to the increased heat generated from driving.


Jeff

they;re new snow tires on a jeep cherokee, i think it may be 30 right now

I've got no scientific basis for this, but I never run below 30psi. I also like to closer to the max as opposed to the min, Better feul milage, even if the ride will be a little rougher.