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 From: "Megrette Hammond" <megdanh@comcast.net>
 To: "North American Fruit Explorers" <nafex@lists.ibiblio.org>
 Subject: Re: [NAFEX] Accurate well defined hardiness map.
 Date: Thu, 22 Dec 2005 21:03:37 0500
Hi All,
Here's my 2 cents worth.
I'm guessing that these maps are accurate and mean exactly what they say they
mean. They just don't mean what we want them to mean.
The Hardiness maps divide the country
into 10 degree zones based on the average lowest temperature encountered over
the winter. I'm in zone 5 so my average lowest temperate is 10 to
20. That means one year of a 30 lowest followed by a succeeding year
with a 10 lowest temperature keeps me exactly at zone 5. If I had 10, 20,
or 30 years of encountering 30 lows with few offsetting "warm" winters the
average would start pushing me to zone 4.
To get some idea of the lowest
temperature you are likely to encounter for a winter (which is what I believe
most people think the maps mean) you would have to know the standard
deviation. That is a measure of how much of difference from the
average (the mean) is contained in the data set in
question. This will tell you if the bell curve around the mean
looks like a pointy Christmas tree (very little variation) or like a
wave in the middle of the ocean (a lot of variation). You would also have
to assume that the standard deviation looking backward is the same as that
looking forward (global warming anyone?). Finally you have to determine
your confidence interval, that is how much of the bell curve you want to chop
off. 95% is a common confidence interval. That means you can say
that you have a 95% chance of having the lowest encountered temperature within X
degrees of the mean. That doesn't tell you that next year won't be one of
the 2.5% years that are extra cold or extra warm. I don't think this
standard deviation data is readily available.
Maybe the climate zone map
people publish exactly how they do their computations. If so find it
and become friendly with an actuary, stats professor, or some other professional
who help you decipher what it will really mean to you.
Good luck growing.
Dan Hammond


[NAFEX] Accurate well defined hardiness map.,
Jwlehman, 12/21/2005
 Re: [NAFEX] Accurate well defined hardiness map., tanis cuff, 12/22/2005
 Re: [NAFEX] Accurate well defined hardiness map., Megrette Hammond, 12/22/2005
 <Possible followup(s)>
 Re: [NAFEX] Accurate well defined hardiness map., Jwlehman, 12/23/2005
 Re: [NAFEX] Accurate well defined hardiness map., Erdman, Jim, 12/23/2005
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