You're right, the cool weather can cause pressure to drop but it should have moved back up as the tires warmed up from driving. Over time, tires will very slowly lose some pressure so the only way to know is to actually check the pressure. If the pressure is normal then you have some malfunction is the TPMS. Could also be a case of the tires are simply low and need to be topped up...
2011 Space Grey E90 M3, DCT, Comp. Pkg.
1997 Z3 2.8, Artic Silver, Tanin Red interior, MT
1974 2002tii, Inka, 5 sp manual