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Jan 222013
Lush crops on fertile land - and massively enhanced by good weather.

Lush crops on fertile land massively enhanced by good weather.

This is the second part of a two-part article on retreat weather issues.  Please click to visit the first part, What Sort of Weather to Hope For at a Retreat Location.

Growing Degree Days

Growing degree days (GDD), and sometimes referred to as Growing degree units (GDU), add an extra layer of sophistication to the growing season measurement that was discussed at the end of the first part of this two-part article.

Growing season measurements don’t distinguish between a season marked by glorious warm to hot days and cool evenings on the one hand, or cool to cold days and cold nights on the other hand.

But, for sure, plants definitely grow at different rates depending on the day’s warmth, and so the GDD calculation is designed to reflect the time it will take for crops to be ready to harvest, expressed in GDUs.  Areas with more GDDs will have faster better crops and more opportunities for double crops.

The calculation for GDDs is not difficult – basically you average each day’s maximum and minimum temperature and subtract it from a ‘floor’ temperature.  For example, if a day had a minimum temperature of 55° and a maximum temperature of 85°, with a floor or base temperature of 50° would calculate to (85 + 55)/2 – 50 = 20 growing degrees.

The concept is explained more in this Wikipedia article.

Growing degree days are another rule of thumb approximation, but the approximation gives a useful measure of the weather related fertility you can expect from an area (while ignoring soil fertility issues, water, pests, etc).

There’s no reason – in theory – you couldn’t get even more sophisticated, tracking growing degree hours instead of growing degree days.  But a practical limitation for this is that most locations don’t have hourly temperature records stretching back many years so as to give you the hourly information you need for each day of the year or season.

Temperature – Heating and Cooling

The last couple of factors have all been to do with growing crops.  But there’s another important weather related factor – your own comfort.

Clearly, you want your retreat to be able to maintain a reasonably comfortable temperature all year.  Even if you economize as much as you can, you’ll still want to keep inside temperatures somewhere in the 60s during the winters and somewhere in the 70s during the summers.  When temperatures go above or below that range, your personal comfort, health, happiness, and productivity starts to severely decline.

Equally clearly, the colder it is outside, and the more of the year it remains cold, the more heating you’re going to need to keep your retreat warm.  Sure, you’ll super-insulate the building structure, but even so, you’ll need some amount of supplemental heat during the winter – and possibly some sort of cooling capability in the hottest parts of the summer too.

You can get an immediate idea about the temperature range simply by looking at monthly temperatures.  Don’t just look at the average for the month, look also at the average high temperature and the average low temperature.  Sometimes it is possible to also see the maximum high and low temperatures too.  If you have all five of these numbers on a graph, you get a sense of the likely, typical, and unlikely best and worst case scenarios, month by month, and that information on its own will be enough to clearly indicate how some places are better or worse than others.

If you’d like to be more scientific about this, you can look variously at heating degree days, and/or cooling degree days.  Some sources of weather data show only heating degree days, some show both or combine the two of them into one single number.

This calculation is very similar to the Growing Degree Day calculation for plants, but uses different baseline numbers (most commonly 60° or 65°) and instead of considering what is best for horticulture, considers what is best for us.  Note that if you are comparing HDD values from different sources, you need to check they are using the same baseline numbers or else you’ll not be fairly comparing similar data.


Wind can be both a positive and a negative factor.  A propensity for wind-storms is clearly a negative factor, requiring stronger construction techniques and more careful agricultural policies.  Strong winds combined with a hot dry climate can also magnify the rate of water loss on the ground and in reservoirs too.

Strong winds also make it harder to insulate your dwelling.

On the other hand, mild cooling winds can be a blessing and can aid in natural unassisted ventilation and regulation of temperatures inside your dwelling, saving you energy.

Winds that are reasonably steady in nature may also be possible to be harnessed for electricity generation via wind turbines.  But whereas solar power works both in bright and obscured sunlight, albeit at different rates of power generation, wind power requires a steady stream of wind with a minimum of about 10 mph in order for it to be feasible.  Some wind power cynics say that there’s a rule of thumb you should use – if a place is suitable for wind power generation, it isn’t suitable for living or for much else.  That’s an exaggeration, but only a slight exaggeration.

Wind turbines can be both expensive and maintenance intensive, so generally we prefer solar cells (with 40+ year lives and no moving parts) as a primary source of energy.  But if you have suitable wind patterns, there’s no reason not to take advantage of them.

Slightly more robust are traditional windmills, capable of working with lower wind speeds, and typically used to pump water up from a well to a holding tank – the ones still being made by Aermotor being perhaps the best known.

It is also relevant to understand both surface and upper atmospheric wind patterns so as to understand your potential risk from up-wind radioactivity releases (that sounds confusing – we mean, radioactivity releases where you are downwind of where the radioactivity is released), whether in the form of accidents at power stations and other facilities, or deliberate in the form of nuclear attack.

Ground bursts tend to release the greatest amount of radioactive material, and much of that into the lower atmosphere, so surface wind patterns can give you a clue for your risks there.  Surface winds vary of course, as you know from personal experience, but most areas have predominant directions for their winds, and in determining your risk you need to understand surface wind flows both at the point of radiation release and also more or less along the path to your location.

Air bursts tend to send more radioactivity up into the jet stream, which can carry the radiation long distances – the good news part of this is that the radiation is spread far and wide and is distributed in a more even and less concentrated form than with the radioactive material from a ground burst, which not only generates a huge amount more radioactive material (hundreds of times more) but also dumps it in a much more concentrated and localized area within a few hundred miles of the event.

Unlike ground winds which might be northerly today then southerly tomorrow, jetstream flows change only moderately and, for the US, flow predominantly in an easterly direction, with the western part of the US having a SE direction, the middle region more or less directly E, and the eastern states a NE direction.

Snow, Ice, Severe Cold

The amount of snow you might receive impacts on several issues.

The first issue is roof design for your retreat (and all other structures on your property).  The greater the snowfall, and the greater the depth of snow that lies on the ground, the more weight of snow that can be expected to lie on your roof – at least until you modify your roof design for a steeper slope.

The second issue is one of transportation.  Without an ongoing program of snow plowing and silting roads, it is entirely possible that you may find yourself snowed in for months at a time each winter.  In a Level 2 scenario, you might choose to use a tractor powered plow for some local snow removal, and a snowmobile for traveling to nearby towns, but longer term, in a Level 3 scenario, you need to consider how you’d manage ongoing winter transportation.

We suggest that year-round access between your retreat and any local population centers is desirable, not only for trade but for support purposes too.  What say, for example, you have a medical emergency.  How would you get to a doctor (or the doctor get to you)?

This is not a problem with an obvious or easy solution, and requires some research to uncover not just the snowfall patterns for your region, but how the fallen snow will translate variously into solid ice and/or hard packed snow, compared to deep drifts of snow, and the type of route you’d normally travel to a nearby community.

Depending on the severity of the snow fall and winter in general, you might need to have shelter – and maybe even some heat too – for your animals to winter-over in as well.

One more thing to do with extreme cold.  Your water supply.  Will you need to invest in additional design considerations in order to protect your water supply and piping so that it doesn’t freeze in the winter, and remains capable of still assuring you a reliable supply of water as needed?


Weather is close to impossible to predict, and its normal variations can sometimes exceed those anticipated by people who have not adequately allowed for random and cyclical variations.  This is an inconvenience in normal times, but can cause starvation and worse in a Level 2/3 situation.

Anything that can be done upfront to optimize the weather issues as part of choosing a retreat location will be enormously beneficial.  Better weather will allow for a more product retreat community, creating more ‘wealth’ (ie surplus food) while requiring less ‘cost’ (energy and time) to produce.

Use the weather categories in this and the first part of this two-part article to compare and rank different locations and to help you select the best location for your retreat.


David Spero[suffusion-the-author display='description']

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