Saturday, May 2, 2009

Picking Your Destination: What will the weather be like?

We get lots of questions about the weather from cyclists headed overseas.
What's the temperature?
What's the likelihood of rain? The photo above, for example was taken in late June in Kaliningrad, Russia with a group of cyclists. A summer downpour soaked us that day and we just had to go to plan B - put on our rain gear and follow plan A!

This article will direct you to the best weather and climate sites on the web so you can answer these questions yourself. And, so you'll know when you might want to take full rain gear, pants, jacket and all versus just a light rain jacket.

Guidebooks offer little help with weather and climate by providing "average temperatures" by month. What good is it to know that the average temperature in Paris in June is 62 degrees F.? Unless you know that averages like this are derived from the daily average of the high and low temperatures averaged over thirty days in June, you know next to nothing!

Average Temperatures - How Useful Are They?

Some guidebooks have now begun to provide average highs and lows per month. This helps a little more to know, for example, that the average low temperatures in Paris in June are in the low 50s F. (51.8 to 55.4 F. to be precise) and that the highs are around 70 (66.2 F. to 73.4 to be precise).

For active travelers who are often outside from morning until near sunset these highs and lows are very important and to know the slight changes that occur during the course of the month can be quite useful, especially during spring and fall. To use a different example, look at the temperatures in Tuscany in October: average highs in Florence are about 70 F. and lows are 50 F. But from October 1 to October 31 the average low temperatures range from 45 F. to 54 F., enough to cause you to throw in an extra long-sleaved jersey or two but not a lot to worry about!

So bring on the wonderful world wide web. Here's So you can find daily temperature averages for many places around the world. This article is interested only in Europe so we'll focus examples there, but learn to use this information and you'll be able to plan your packing for "average daily temperatures" at your destination.

The best web site I've found for this is the UK weather site where you'll find climate data for Florence, Italy which I've described above.

The best way to get to know these climatic statistics is to compare with a place you know well. Try your hometown or place of residence, for example. That way you can use the sensors you know best - your bare arms and legs!

A Colorado Weather and Climate Example

I'll use the example of Fort Collins, Colorado where we are based. If you replicate this exercise using your own town (or nearby town with climate data in the event your town is too small to be reported) you'll have a good understanding of climate and weather in your destination.

Fort Collins normally has a wonderful Indian summer in October. Bicycling and hiking in the foothills of the Rockies is wonderful, but it can be cold, especially in the morning. Here are the data:

Average monthly high temperature: 65 F. (not so bad)
Average monthly low: 35 F. (whoa! Chilly)
Monthly mean: 50 F. (not that great!)
Sounds pretty cold, actually.
But the range in monthly averages is very different:

Average range of monthly highs from Oct. 1 - 31 is from 71 degrees F. in early October to 57 F. in late October (indeed, until Oct. 15 average highs are above 66 F).

The average range of monthly lows is 41 to 29 F. (if you live in Colorado you know that you aren't in any hurry to start a bicycle ride early in the morning, but that after 9 o'clock, it warms up quickly!)

Look back at the Florence data in Italy and you see that the lowest average low temperature is 45 F. That's nothing for someone from Colorado! (Now if you live in Sacramento you know that your average lows range from 47 F. to 54 F.) You'll feel right at home in Tuscany in October!

Here's where to find these sites to begin your own personalized climate and weather odyssey.

For Climate data in Europe (usually calculated using averages collected over a 30 year period)
For current weather in Europe
For U.S. weather: You have to enter the name of your city or a nearby city to get weather data. Here I'm using Fort Collins:
Once you've found current weather you can get long range climate data by scrolling down and click on "Averages" (to the right of "36-hour forcast") to find your long term highs, lows, and rainfall.

See this example of Fort Collins climate data.

What about the rain?

I have not been able to find reliable, current, daily average precipitation data. They are collected, but apparently not widely reported yet on the web. In the sites listed above you will find average monthly precipitation. What is even more useful, if you can find it, is the number of "rain" days per month as well as total monthly precipitation. In August Dublin gets 7.1 cm. of rain (about 2.8 inches). Milan gets 9.7 cm. (3.8 inches). The difference, of course, in Milan is that all this falls in afternoon thunderstorms on, perhaps 8 days while in Dublin this is often ongoing drizzle 20 days in the month! It won't rain all day, mind you, but the day may begin with drizzle and end with sunny skies.

If you are aware of a good weather and climate site with good global precipitation data please let me know:

The Bottom Line

We've been talking 30-year averages with all this. That means that you could go to Tuscany, Paris, or Ireland in an "off-year" and freeze to death OR enjoy unseasonably warm and clear weather. So always, in spring and fall, take rain gear and warm weather clothing. In northwest Europe ALWAYS take rain gear and warm clothing (this includes northern Spain).

A few myths about weather and climate

Once you know the latitude of a place you understand the weather and climate.

Wrong! Relative location to other features on the surface of the earth is far more important than latitude, especially in the mid-latitudes. What is "upwind" of your destination influences the climate more than latitude. Try Ireland in January, for example. Dublin is north of 53 degrees north latitude yet average low temperatures in January are 37 degrees F. Milan, at about 45 degrees north latitude averages 25 degrees F. as a low in January!

The difference is that the North Atlantic Ocean (and, to a lesser degree, the Gulf Stream) acts as a huge heater keeping Ireland warm in winter while Milan sits in a basin surrounded by mountains where it gets pretty cold in winter.

Here's a great web site about common misconceptions and misunderstandings about weather and climate.

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