I think that a snowfall would pretty much be the same as a frost to a dahlia. As long as the ground doesn't freeze and damage the tubers (which it shouldn't for quite awhile yet), you can still dig and store them as you normally would. I would cut them down after the snow, leave them for a week or two, and divide and store them as usual. You might want to cut as many flowers as you can to enjoy before the snow comes and puts an end to your dahlia season, though.
I'd also like to say I have only been planting dahlias for a couple years, so if any of the more experienced and knowledgable folks have better info, I defer to them!

Thanks MommaCarp. The problem is, I wouldn't know if the ground is going to freeze with the snow or not. So if I cut them down after the snow, I'm afraid I would be too late. Or would the snow actually act as insulation? Or should I just dig them up today?

The ground will not freeze right away. Check your forecast...what is the weather supposed to be in a couple of days? If you normally don't get cold weather until the end of November, you probably won't get frozen ground until then.

According to the forecast, our high is 40F, and low is 28F for tomorrow. Same with Sunday. On monday, the low is finally going to be above freezing.

What do you think? Will it be enough to damage the tubers?

Dahlias in the ground can be dug in the snow. But realistically, if this is an early snow, it will melt.
I would start digging very soon, however. It is not so much that the tubers will freeze but that you cannot push the shovel though the frozen couple of inches of soil above the clumps. Dahlias will freeze and be lost if the ground freezes about 6 inches deep. I started digging a few weeks ago and will be done before the ground freezes here.

Alright, I'll try to dig the dahlias tonight. Thanks a lot for the advice, everyone!

siichan- Put...the shovel...down. It will be a while before your ground is frozen even 2 inches down. Let the snow kill them off, let them sit for 10 to 14 days and then dig them. Unless your temps drop into the low teens...for a couple of days straight, the ambient heat of the soil will not let the ground freeze very deep.

tj

Eeeeeeeeekkkkk!! Oh no, I just dug them up! :((

sigh... Oh well, next time I'll remember not to be so quick with the shovel...

When I start digging about October 15th each year, the temperature is in the 60s. The tubers dug this early do just as well in storage as the ones dug later. Here we do not have killing frosts until mid November and waiting for a frost means digging in cold wet, weather. I am not into that. Many of you want to savor your last blooms before the frost and I can relate to that. But that means you will be digging in cold conditions.