2001 Chevy Silverado Oil Pressure

It was about 13 ° this morning at my house, approximately 0 ° with the windchill. I preheated my truck as I do in the winter. After I got in 10 minutes later it was barely starting to get warm which didn't suprise me since it was so cold. I did notice however that my oil pressure which typically runs at about 60 lbs. Was at 50 and didn't get up to 60 consistently until my truck was completely warmed up. Until it was completely warm it would stay at about 50-55 and raise to 60 when I was accelerating, likewise when I was sitting idling it would drop back to 50. Could this just be caused by the cold or should I be concerned about it; also if it something I should be concerned about what could the problem be? (The change oil light did come on the other day but the oil is still completely yellow and clear so I haven't gotten around to changing it. Wasn't sure if this could have anything to do with it or not but I figured I'd mention it.)