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Old 01-28-2012, 09:01 PM
Location: IN
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Originally Posted by J&Em View Post
The same articles quote the meteorologist who helped create the map that there isn't enough data to make any such claim. The map was intended to reflect coldest averages not trends and not the most extreme temperatures ever recorded. Much as a lot of people want to believe every warm day, season, year or even decade is an indication of a long term trend, we have had so many warm and cold cycles come and go just in the period of written history that a 13 year or even a 30 year period is a comparative sneeze. As Bulldogdad mentions La Nina and El Nino cycles have made differences, as have sun cycles. The media makes it sound so simple but there is much, much more to it.

The map makers attributed much more of the changes in zone to better data than any real big weather changes. The two maps begin nearly at the same time (1974 and 1976) but one stopped after 13 years the next covered about 30 years. The difference is a mere decade and a half. The second was more the one that was based on more precise data as well as being more recent. The media loves sensationalizing any numbers which always winds up trivializing the real science. Knowing all of this why would the USDA want to make a political statement based on such a short term and limited temperature measurements?

All climate research models indicate more drastic changes in weather patterns. There can be more extreme cold as well as much warmer temperatures as any overall climate changes take place. It's one of the reasons "global warming" is no longer used to describe the probable changes. Reading about the map making process lets one see they made every effort to take into account local topography/geography, even urban heat islands, and they increased the numbers of places temperatures were recorded. There will always be small areas with big differences that will be missed. Both maps are composed of average lows, occasional outliers cannot be included as an "average". It is a reference for average cold winters so that people know generally what plants will survive and which ones will almost never make it. It isn't possible to reflect both unusual lows and averages in one map so it cannot be "accurate" for extremes. There was an extremely low temperature recorded in my area a few decades back of -24F. If they had used that as the number to base the map on I would only plant plants that could survive in what is labeled zone 4 right now on the map. I'd be missing out on the many plants that do grow here in a zone 7 about 99.9% of the time. If I followed this "accurate map" I could wind up losing half of those plants to the heat because they cannot survive the heat of this zone. Hardly something useful then, is it? Expecting it to reflect uncommon record cold would make the map useless for what its true purpose is: an excellent tool for telling you the kinds of plants that can be planted and survive in your area.

Exactly.... just less verbose.

SCGranny that was the flip side of the increased numbers of places they have recorded temperatures from. There were places not accurately represented because they were extrapolated from data nearby that wound up being different once they were really recorded. I'm sure most of your plants won't know the difference if they've made it so far.
Zone 4 would still be the correct call if one out of every two or three winters records a low temperature of -20F or colder. It surely wouldn't make sense to try to grow plants and trees acclimated to zone 5 or 6.
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Old 01-29-2012, 04:57 PM
Location: Bangor Maine
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According to the older zone I am in 5 but I have always planted some zone 6 plants and they grew just fine.
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