The valley flatters you

A still, mild morning in the car park at the foot of the fells tells you almost nothing about what is happening several hundred metres above your head. Temperature falls by roughly one degree for every 150 metres of ascent, so a pleasant 12°C in the valley can easily be 4°C on the summit — and that is before wind chill takes its share. Add a steady 40 mph gust and it feels closer to freezing. Hill ranges make their own weather, and the valley you set off from belongs to a different climate. Treat the first hour of any walk as a border crossing.

Read the forecast properly, not just the symbol

A little sun-and-cloud icon tells you almost nothing useful. Mountain-specific forecasts are far better, but you have to interrogate them. Before you leave the house, ask yourself a handful of blunt questions:

• What is the trend? A forecast for "rain later" is very different from rain arriving at 10am. Note when conditions change, not just whether they do.
• Where is the freezing level? This tells you whether you are dealing with wet sleet, hard neve, or simply cold rain. It matters enormously for footing and for your hands.
• What is the summit wind speed and direction? Valley wind figures are close to useless. Look for the speed at 600–900 metres and, crucially, the gust figure alongside it.
• How high is the cloud base? A forecast that reads "cloud free above 700 metres" is a gift. One that reads "cloud on the tops all day" means compass work and careful pacing.
• What is happening upwind? Weather arrives from somewhere. If the west is already turning, the fells will follow within a few hours.

Cross-check two or three sources rather than trusting one. If they disagree, plan for the worse of the two and you will rarely be caught out.

Clouds are a live forecast

Once you are on the hill, the sky is the most current information you have. Learn half a dozen signatures and you can read the next few hours reasonably well.

• Lens-shaped or lenticular clouds sitting above a ridge mean strong winds aloft and a standing wave. Expect buffeting on exposed ground.
• A cap cloud clinging to a summit means moist air being forced upwards — the tops will be clagged in and damp, even if the valley is bright.
• Thin streaks of cirrus thickening and spreading, sometimes called mare's tails, usually signal an approaching front. Wind will strengthen and rain is often 12 to 24 hours behind.
• Cumulus building vertically before midday is a warning of showers, hail, and occasionally thunder. Get off high, exposed ground if towering clouds develop an anvil shape.
• A halo around the sun or moon is a classic sign of a warm front sliding in. Rain is likely within a day.
• A sudden darkening with a drop in wind can precede a squall line. Brace for a sharp, short-lived blast.

Notice also how fast cloud is moving and at what level. Fast, low cloud scudding over a ridge is a strong hint that the wind up there is far stronger than it feels where you are standing.

Wind is the underestimated hazard

Most hill days that go wrong involve wind and cold rather than anything dramatic. A rough guide: 20 mph is noticeable, 30 mph makes walking hard work, 40 mph has you leaning and staggering on exposed ridges, and 50 mph or more on a summit is genuinely difficult to stand up in. Gusts add another 50 per cent on top of the average, and ridges, cols and plateau edges funnel and accelerate the flow.

Wind chill is what actually bites. A 5°C summit temperature with a 40 mph wind feels close to freezing, and hands and faces lose function quickly. That is why a hat, gloves, and a spare insulating layer belong in your pack in July as well as January. If you cannot hold a map steady or open a zip, you are already losing the fine motor control you need for navigation and decision-making.

A five-minute routine before you set off

Stand at the car, look at the sky, and run through this:

• Confirm the wind speed, direction, and gust figure for the summits you intend to visit.
• Check the cloud base and the timing of any rain or snow.
• Note your turnaround time and write it down. Stick to it.
• Pack for the worst conditions forecast, not the best. Waterproof shell, spare insulation, hat, gloves, head torch, map, compass, and an emergency shelter.
• Tell someone your route and your expected return time.

Then, once walking, reassess every hour. If the wind is stronger than forecast, the cloud lower, or your group slower, adjust the plan rather than pressing on and hoping.

Make the call early

The hardest decisions on the fells are made at a decision point, not at the summit. Turn back while you are still warm, dry, and thinking clearly, and the day remains a good one. Push on into worsening weather because you have driven three hours to get there, and you hand the decision to the conditions instead. The summit will still be there next month.