If it is getting that low it is time to harvest them; they are possibly damaged by temps in the teens, but should probably be ok. I am not sure of your location but with that weather and this time of year they are surely done growing. They freeze great. But if you are keen on fresh leeks they can survive until winter starts getting serious.

Your leeks may very well be completely hardy in your country, depending on specific cold snaps. Does your ground ever freeze? and then stay frozen? You may wish to leave your leeks in the ground and mulch them up to make sure the ground stays thawed and then only dig them as you need them for the table.

For comparison the ground here in central Minnesota freezes down to close to 4 feet deep every winter. Lakes can get up to 2 feet of ice on them. Not what you experience at all. Here leeks would get frost killed for sure, but walking onions, garlics, some of the multipliers take this in stride. It is much milder for you, and is very likely mild enough that you can plan to winter your leeks over with a decent amount of mulch to keep the ground around them thawed enough to dig when needed. You will need to pay some attention to the hardiness of the leeks you plant, it varies some by variety.

I googled sunset zone 2b and it looks like it is a USDA zone 5 (-10F to -20F). Probably fairly comparable to the Minnesota winter.

I have also read that there is bizarre historic arctic air currently setting up shop in the NW, while winter is failing to materialize over the actual arctic.

I just harvested the last of my leeks yesterday. They had endured a couple nights around 20d the weekend before Thanksgiving and were still in perfect shape.

It looks like most of the US and Canada will be getting a 'polar vortex' type cold front moving thru mid week. We are predicted for high single digit lows on Thursday and Friday morning here. The ground will surely freeze solid in a lot of the continent so if you are going to harvest them I would do it now. They are often tough to dig out of thawed ground.

Jack,

just guessing here but the original poster is very likely in the far West, since using the Sunset system. The polar vortex that is due through the midsection of the country may not affect him at all. I am guessing that your ground and mine will freeze solid over the next week and we will be seeing ice on our lakes, too. As far as around here goes it only looks to be seasonal or just a bit below, but the jet stream will be dipping real far south. For us there are no below zero temps forecast; so it really isn't going to be all that bad around here, even into the 40's tomorrow but that will be the last above freezing around here until maybe Christmas or after.

BTW very little of Minnesota is zone 5, I sit right on the edge of 4b/5a almost in an island due to the heat island effect here in the Twin Cities, but most of central and south Minnesota is zone 4 and at least the entire upper third is zone 3. Zone 5 is more like central Iowa/Illinois than Minnesota. Furthermore the zone 4/5 boundary is a real barrier for a lot of plants otherwise hardy into zone 5. Global warming is confusing that for sure. I ran a zone 4 hardy perennial nursery for 12 or 13 years here; so I have some direct experience. We certainly are milder than we were back then, but I am not so sure that it is a full climate zone milder, not just yet.