How to read a climate chart before you book
Average temperature is the most misleading number in travel planning. What the averages hide, why rainfall matters more than people think, and how to spot a bad month before you pay for it.
Every destination page on the internet shows you a monthly average temperature, and almost nobody explains what it leaves out. Used carelessly, it is the fastest route to packing wrong and booking the wrong week.
An average is two numbers pretending to be one
When a site says a city averages 20°C in April, that figure often blends the daytime high and the night-time low. A place with 27°C days and 13°C nights averages 20 — and so does a place that sits at a flat 20 all day. Those are completely different holidays, and you would pack differently for each.
This is why Fairweather charts the average daily high rather than a blended figure. It answers the question you are actually asking — what will it feel like when I am outside doing things — and it is the number worth comparing across cities.
The practical consequence: inland and desert destinations swing hard between day and night. Marrakech in March is pleasant at 2pm and genuinely cold at 10pm. Coastal and island places barely move. Always assume a bigger gap the further you are from the sea.
Rainfall in millimetres is not rainy days
Two cities can both record 60mm in a month and have nothing in common. In one, that arrives as a light drizzle spread across eighteen grey days. In the other, it lands in two spectacular tropical downpours that clear inside an hour, leaving twenty-nine sunny days around them.
So read rainfall as a shape, not a score. Look at the pattern across the whole year: a tall bar surrounded by short ones usually signals a defined wet season, which is often survivable if you plan mornings. A long run of medium bars is the genuinely grey scenario — that is the one that spoils a walking holiday.
Averages describe decades, not your week
Climate averages are built from thirty years of records. They are excellent at telling you what a month is normally like and useless at telling you what next Tuesday will do. A city whose September average is 26°C will still hand you a cold, wet week now and then — the average simply says the odds are strongly in your favour.
Use averages to choose the month and the destination. Use an actual forecast in the last week to pack. They are different tools and they are not interchangeable.
What to look for, in order
- The shape of the temperature line. A gentle curve means a forgiving climate; a sharp peak means a brutal short summer.
- Where the rainfall bars cluster. Avoid booking into the tallest run unless the trip is specifically indoors.
- The gold months. On Fairweather these mark where good temperature and low rainfall overlap — the months locals would pick.
- The month either side of your dates. If both neighbours look better, moving your trip by two weeks is usually cheap and always worth it.
Every Fairweather city page charts the average daily high against monthly rainfall and highlights the prime months in gold, so all four of those checks take about fifteen seconds.