New United States Department of Agriculture hardiness map features more up-to-date climate data and interactivity. Here are the strengths and limitations of the latest update since 1990.
Here's the link http://planthardiness.ars.usda...

Thanks for the link Paul!

This will help some who don't know their climate zone, but for So. Cal. it is close to useless. I'll stick with Sunset Western Garden zones.

Thanks Paul. It is better than the previous version.

It confirmed that my area is one zone higher than the nearby city zone (which is what comes up when you use a zip code search.) Being new to the area and having never gardened here, it was very helpful.

We had a discussion about that here:

The thread "New hardiness zone map" in All Things Gardening forum

Now I keep links to Sunset & "zoomable" USDA Zones in my sig block, PLUS a way to find your local USDA weather station, and freeze-frost dates.

But I agree - the "average winter low" doesn't tell you much.

I heard about this but in I know we get way colder than the average lows.
I'm suppose to be Z 5b but I'm more like Z 4 in my rural valley setting
although this winter was unusually mild.