Correction:
"Zones in this edition of the USDA Plant Hardiness Zone Map (PHZM) are based on 1976–2005 weather data."
http://planthardiness.ars.usda.gov/PHZMWeb/AboutWhatsNew.aspx

More detail:
"The zones in this edition were calculated based on 1976-2005 temperature data. Each zone represents the average annual extreme minimum temperature for an area, reflecting the temperatures recorded for each of the years 1976-2005. This does not represent the coldest it has ever been or ever will be in an area, but it reflects the average lowest winter temperature for a given geographic area for this time period. "
http://planthardiness.ars.usda.gov/PHZMWeb/AboutMapMaking.aspx

So..... Then why am I zone 3 or 4? My average low for nauary is -23C. Does that not make me zone 6 by that logic?

Jesse- NO NO NO! It's the average EXTREME low for each winter that defines your USDA zone. If you look at Minnesota on the new map, and extend it out, it looks like you're 3b/4a!

oh man! I slot right inbetween 6a east and west of me! 🙁 I think I was downgraded to a 5b....

Don't know that i can believe this, It has me at 7a..seems a bit too hopeful!!! 😕

How accurate does anyone here think that map is to them??? I don't think for my area it's accurate at all.

It isnt too bad up here. The hard part, is finding the areas where the zones change. With in 24km, the zone goes from a cold zone 5 at the lake shore, to a cold zone 3 (where the airport is), and there are some zone 2 that fit into city limit. I can get away with hibiscus here, and an hour drive west, you can barely grow daylilies. I use the zone as a bench mark, and plant what ever I feel needs to be planted, and hope for the best. The plants are a better indicator of zone (especially long term plantings), then some human contrived map IMO 😀

How accurate does anyone here think that map is to them??? I don't think for my area it's accurate at all.

Mine is close, but my avg. for the area is a zone 5b just like the old map shows and I got this figure from warmer years that than have all together?
But I think they did well with the place I lived on the snake river with the up-grade. 😀 But I don't think any place in Idaho is a zone 7b like they have now. 😆

What I don't get is why USA map does not jive with the Canada map in the North-West part of Washington? Shows it warmer in the Washington map? 😐

The Canadian map is crap. It factors in other variables and tends to exaggerate the zone ratings by .5-1.5 USDA zones... A real shame because there are all kinds of Canadians who now think they're in zone 6, when in reality they live in very cold zone 5's! This used to really get to me when I'd see a post from someone in Montreal saying 'Zone 6' or Toronto saying 'zone 7', which is simply not the case!

I, for one, find this new map very accurate, and imagine that for any area if you go back and look at the data, will find it bang on the money! I think there is even a feature that will let you see the average extreme minimum low for the period for any given area. It's pretty in depth actually!