How many rainy days is too many for a trip?

The number of days tells you how often it rains, not what the rain costs. Count instead the hours of rain inside the window when you will be outdoors, and note at what time of day they fall.

Rain days or rain hours?

By Matthieu Silbermann

In one sentence

Rain is read in hours during the activity day, not in rain days: a forty-minute shower makes a rain day and spoils nothing, while three hours of rain between nine and noon kill the day. Counting days measures how often it rains; counting hours measures what the rain costs.

Before you book, read the hours of rain during your activity day, not the number of rain days. A day with a forty-minute shower counts as a “rain day” and spoils nothing.

What each number measures

You read that a coast has rain on nearly one day in two, and you give up. But counting days measures how often it rains; counting hours measures what the rain costs. Frequent, brief rain makes many rain days and few lost hours.

On our stays in Iceland and Norway, the rain that actually fell was low while rain-day statistics announced much worse; elsewhere, rain really did cancel planned hikes (our trips). It is not the same rain, and that is exactly what counting in hours brings out. The definition is that of rain hours.

The position of the hours counts as much as their number

Three hours of rain in the evening block nothing. The same three between nine and noon kill the day. The window in which you are outdoors shifts toward the morning when the day is long or the effort high: that is the window to count in.

Wind is a separate blocker

Wind only counts for exposed days: crest, ridge, summit, cliff. On a ridge, you give up in strong gusts under a dry sky, and you set off in drizzle when it is calm. A day that passes none of those places need not take it into account.

Reading the rain before you book

Five moves.

Define your activity window: the hours you will be outdoors.
Use recent hourly records for the month you are considering, not climate normals, which already lag behind the current climate.
Count the hours of rain inside your window and note when they fall: morning or evening.
Treat wind separately, for exposed days only.
Keep the result for what it is: optimistic.

Heat takes hours away from the day; rain makes you look at when it falls. What is your heat ceiling? deals with the first, and It isn't the north you're looking for puts the two together.

To place a day with no plan: Where to put the day with no plan.

What this count does not say

The count says nothing about intensity, or about how long a disturbance lasts. It treats each day on its own, whereas a front often lasts several days (meteorological order of magnitude). It is therefore optimistic: an extra week cannot be bought like insurance against rain.

What you can do with it

In the itineraries we calculate, rain is counted in hours over the activity day, not in days. Early access.

What we do not know

Our observations come from a few stays: they illustrate the count, they do not prove it. We have not tested the method on coasts other than those of our stays.

We give no threshold of rain hours: it depends on what you came to do, and on the window in which you do it.

Method definition and observations from our trips. No rainfall statistics with figures are used on this page.

A figure looks wrong to you, or your own experience of rain says something else? Write to us — corrections are published.

Frequently asked questions

Should I look at rain days or rain hours?: At the hours of rain during your activity day. A day with a forty-minute shower counts as a rain day and spoils nothing; three hours of rain between nine and noon kill the day.
How many rainy days is too many for a trip?: The number of days tells you how often it rains, not what the rain costs. Count instead the hours of rain inside the window when you will be outdoors, and note at what time of day they fall.
Does wind count like rain?: No, it is a separate blocker, and it only counts for exposed days: crest, ridge, summit, cliff. On a ridge, you give up in strong gusts under a dry sky, and you set off in drizzle when it is calm.

Method — Method definition (rain hours) and observations from our trips. No rainfall statistics with figures are used on this page.