Chasing conditions: how weather affects your climbing

Spend a season climbing outdoors and you will start doing something that looks faintly unhinged to non-climbers: checking the temperature and humidity for a crag you might visit in a fortnight, and feeling genuine emotions about the result. There is method in it. The same problem can feel a full grade harder on a warm, damp afternoon than it does on a crisp, dry morning, and learning to read that is a real skill.

Why cold and dry wins

It comes down to friction and skin. When rock is cool and the air is dry, your skin grips better and small holds feel more positive. Warm rock gets greasy under the fingers, and a sweaty hand on a sloper might as well be buttered. This is why climbers talk reverently about "sending temps", usually meaning cold but not freezing, with low humidity and ideally a bit of breeze to keep the holds dry.

The effect is most dramatic on hard, friction-dependent climbing. Crimps, slopers and smeary footholds reward good conditions enormously. On big juggy routes where you are mostly hanging on by the bones of your fingers, conditions matter far less. So the harder and more marginal the climbing, the more the weather decides the day.

Reading a forecast like a climber

A standard weather app tells you whether to take a coat. You want more than that.

• Temperature: cooler is generally better for friction, though painfully cold fingers go numb and clumsy, so there is a sweet spot rather than a colder-is-always-better rule.
• Humidity: arguably the bigger factor. High humidity leaves a film on the rock and on your skin. A cold but muggy day can climb worse than a slightly warmer dry one.
• Wind: a light breeze dries holds and chalk and keeps your skin from sweating. Too much and belaying becomes miserable.
• Recent rain: porous rock like sandstone holds water for days and is fragile when wet, so it needs proper drying time. Limestone often sheds water faster. Knowing your rock type tells you how long to wait.

Aspect matters too. A south-facing crag bakes in afternoon sun and might be unclimbable in summer but perfect on a cold winter morning. A shaded north face is your friend in a heatwave. Good guidebooks and local knowledge will tell you when each venue comes into condition.

Using a good day well

When the forecast lines up, the temptation is to thrash yourself on everything. Better to have a plan. If you have a project that has been shutting you down, a rare day of perfect conditions is when you go all in on it, warmed up properly and rested, with your best attempts saved for when your skin and energy are freshest.

Conditions decay through the day in two ways. The weather warms up, and your skin wears down. Both push your best window towards the start of the session. Plenty of climbers do their hardest attempts early and save the volume mileage for later, once the holds have greased up and their fingertips are past their best.

Manage your skin like the limited resource it is. File down sharp flappers before they tear, keep your hands clean and dry between goes, and accept that some days the rock simply will not be in nick no matter how badly you want it.

When the weather is rubbish

Not every trip gets the dream window, and chasing perfect conditions endlessly is a good way to never climb. Warm, humid days are fine for mileage, for working the moves on a project rather than expecting the send, or for steep terrain on big holds where friction barely registers. Save the marginal, skin-and-friction routes for when the air turns cold and dry.

Over a few seasons you stop checking the forecast out of habit and start reading it as a tactic. You learn which crags suit which weather, which way the wind needs to come from, and roughly how your own skin behaves at different temperatures. Keeping notes on what the conditions were like when a climb went well, or badly, turns all that scattered experience into something you can actually plan around.