@smashing - A few tips for snake smoking and temp control that some people will agree with and some people will have different opinions about.
Snake
1. Since its cold, you might want to stack your briquettes a little more upright so they will burn from one briquette to the next one a little faster.
2. tight and consistant - make sure you coals are stacked consistantly and there aren't gaps between coals where it prevents the snake from moving from one coal to the next.
3. water pan - Did you have a drip pan with warm water in it? I've found a drip pan filled with steaming hot water helps keep temps from jumping around as quickly and helps get up to temp quicker.
4. If you are not getting results still from the above items and the vent items below, you might want to just add another row of coals on top of your snake. If you are burning consistantly too low, another row of coals should get you where you need and be controllable via vents it if jumps too high.
5. Make sure your lid vent is over the food you are smoking and that it is generally opposite the lit coals. With a snake moving as it burns, it doesn't mean to keep moving things, but just make sure the vent is general on the opposite half of the grill.
Vents
1. I usually run top wide open, but with it being so cold perhaps slightly closed would help keep in some heat (this is the topic I specifically think there will be many opinions on. Some people like me like to always run the top wide open and control temps with the bottom, while others control via top, or partially close the top then control from the bottom)
2. Adjust bottom vent in 15-20 minute increments let it settle in then readjust if needed. If you are running way too cool, its tempting to open the bottom all of the way, but in my opinion you are letting in too much cold air and it's not going to give you the results you are looking for. Opening the bottom wide open works fine for getting your coals to blaze when doing a hot cook, but for smoking I think wide open hinders the result you are looking for.
3. Now that I looked at the pics of your grill, I'd shut down the bottom vents that aren't near the lit coals all of the way and adjust only the vent closest to the flames.