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1) The raw data for these plats comes largely from 50
year averages at NOAA weather stations.
The locations of the stations are marked on the maps.
Sunshine and Relative Humidity were not available for all the stations, so
those plots are even less accurate. |
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2) My general procedure was to generate the type of data
used by Gladstones in his book 'Viticulture and Environment', and other
writings, as a way to compare different sites. Notably, he uses a
'Growing Degree Day' that has been modified to reflect the physiology of
grapes - it accumulates from 10C to 19C - and is capped at 19C. That's a bit
different from the 'GDD' in the weather station tables - which isn't capped
and is in Fahrenheit. I did my best to generate equivalent
figures. My estimate of the 'Temperature Variability Index seems to be
low. |
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3) These maps are spline interpolations between weather
stations. They are not models that take local geopraphy into
account. They are most accurate between points. I have some
reason to believe that they at least reflect general trends in the
region. They have some features in common with USDA hardiness
maps. They clearly show the effect of Lake Michigan (though mid-lake
values must be pretty bogus), and some of them show effects of urbanization
around Chicago and Gary. |
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4) Your milage may vary. Please ask for my
permission before propagating these images. |
And here are the maps:
Some Annual factors: Precipitation, Growing Season (Frost Free
Days), Summer Heat
Comments: The Lake seems to have bigger impact on temperature, than on
rainfall.
You can also see the Lake's moderating influence on the number of Hot Days - MI
has fewer than IL orWI.
The zone of Lake influence is much narrower on the IL/WI side than in MI.
Some Winter Plant Hardiness factors: Days Below 0F, January Daily
Low, Monthly Average Low and Record Low
Comments: Again, the Lake has a big effect on the extremes in
temperature, moderating MI more than IL/WI
The number of Days Below 0F really jumps as you move away from the Lake in
WI.
Growing Season Biological Intensity: Cumulative Growing Degree Days
for Aug-Oct
Comments: This should give an indication of what will ripen, and
when. For grapes, by the Lake in WI, you can
ripen early season Reds. The situation is better in MI, though the latest
season reds are out of reach.
I don't have apple data (yet).
Ripening Factors for September: Daily Mean Temp, Highest
Monthly Average Max Temp,
Temperature Variation Index, Sunshine Hours, Rainfall, Afternoon Relative
Humidity
Comments: Note the warm spot between Chicago and Gary, as with the
Frost maps.
My TVI calc seems to come out low compared to Gladstones - but you can
see the Lake moderating Temp variability.
Sunshine hours don't vary much across the region, nor does rainfall.
Afternoon RH varies smoothly across the region - but doesn't seem to be affected
by the Lake. This could be from the lower number of data points, though.
For grape growers, I'd say that these maps suggest the biggest problem is too
much rain in the fall. Medium bodied reds should do nicely in MI (and do)
- but trying to grow an authentic Port-type wine is probably unrealistic.
I'm trying to discover more about what this means for apple varieties -
especially the British and French cider-types.
