Getting Temps Right ... and Holding them?

TN_VOL_Man

I planned and executed an indirect cook for a Standing Rib Roast over the weekend here in the Charleston, SC area and it was a windy and cold day.  I set the roast on my BGE at 5:15pm and finished it at around 10:30.  The roast was only 4.8 LBs.  I took temp recordings for the Dome, Grate and meat each 15 minutes.   I went ahead and set the roast on the grate at a dome temp of 345 and began bringing the temp down.  Within 30 minutes, the BGE was at a dome temp of 265.  The outdoor temp was 35 at start time and about 29 when complete. Wind was between 2 and 5 mph.   Over the hours, it seemed difficult to hold the temp.  In 15 minutes time, the Dome Temp would change as much as 20 degrees (rarely would it be stable).  Grate Temp has a similar story but not as drastic.   I am not sure why that is.  Anyone know?   I kept adjusting the vents (bottom and daisy wheel) like a maniac. The roast turned out pretty good.  Avg Dome temp: 254.6; Avg Grate Temp: 212.7.    Would this be because the cold windy weather, or a malfunction in the EGG?