Smoker Temp.

[cabinetmkr39]

I'm smoking a 8 lbs. pork shoulder today trying to maintain 250 degrees, Air temp is 27 F smoker actual temp 235 is this normal? If I up temp to 300 it will get there, but it will not stay at 250.
Shoulder was room temp when I put it in a 8 am this morning and smoker was at 250. its now 10:30am
Thanks in advance. using a PB850PS2