Why a Valley Forecast Won't Do

Most of us start with the weather app for the nearest town, and it's a reasonable place to begin — that's where the car will be parked, after all. But the difference between the valley floor and a 900-metre summit is often the difference between a pleasant spring day and a genuine winter outing. Forecasters talk about the lapse rate: roughly 0.6°C lost for every 100 metres you climb, or about 2°C for every 300 metres. That means a comfortable 12°C in the valley can be 6°C on the tops before wind is even considered.

Rain works the same way. Hills squeeze moisture out of the air as it rises, so upland areas routinely see two or three times the rainfall of the lowland towns nearby. Wind, too, increases with height and is funnelled and accelerated through cols and along ridges. The forecast for the village is a starting point; the mountain forecast is the one that keeps you safe.

Wind: The Number That Decides Most Days

If you only check one thing beyond rain, make it wind. Look for both the mean speed and the gust figure, because gusts on exposed ridges and summits are commonly 30 to 50 per cent higher than the sustained wind — and it's the gusts that take you off your feet.

• 20–30 mph: noticeable, especially on the crest, but manageable with a decent shell.
• 30–40 mph: hard work. You'll lean into it, your pace drops, and exposed sections need real care.
• 40–50 mph: exhausting and often unpleasant. Time penalties of 30 to 50 per cent are realistic; a seven-hour day becomes ten.
• Above 55–60 mph: for most hillwalkers this is a day to choose a low, sheltered route or stay in the valley.

Direction matters as much as speed. A westerly gale means a windward slog up the western flank and a buffeting on the ridge, but it also means the eastern corries and woodland tracks may be calm. Plan your line to use the terrain — climb the lee side, save the exposed crest for a short section, and keep an escape route into shelter.

Cloud Base and Visibility

Mountain forecasts give a cloud base in metres, and it's worth taking literally. If the cloud base is forecast at 600 metres and your summit is 980 metres, you will be walking in clag, probably for several hours. That's not a reason to stay home — it's a reason to plan a route you can navigate with map, compass and pacing rather than one that depends on seeing the next cairn.

Consider what poor visibility does to your day. It slows you down, hides the hazards (cornices, crags, steep ground), and removes the views that make the effort worthwhile. It also makes pathless terrain much harder than it looks on the map. If the forecast suggests the tops will be buried all day, a lower hill with a good path can be the better day out. In winter, cloud and a white landscape combine into a whiteout where the ground and the sky become one — that's when accurate navigation and a firm plan for turning around earn their keep.

Rain, Snow and the Timing of Fronts

Precipitation totals in millimetres tell you how wet the day will be, but the timing tells you how to walk it. Twenty millimetres spread over eight hours is a damp but doable day; twenty millimetres in ninety minutes is a soaking, and it will turn paths into streams and bring becks up fast. Look for when a front is due to cross, whether rain is showery or persistent, and whether there's a window in the morning or late afternoon.

Ground conditions follow the rainfall. After a wet week, boggy moorland becomes genuinely laborious, and stream crossings that are usually a stride become a decision. In winter, check the freezing level: it tells you where rain turns to snow, where you'll meet ice on paths and rock, and whether the ground will be firm neve or energy-sapping slush. A freezing level of 900 metres with a 1,000-metre summit means you're in the snow zone for much of the day, and winter kit and skills come into play.

Building Your Pre-Walk Check

Five minutes with a mountain-specific forecast, cross-checked against a second source, is enough to build a clear picture. Look for agreement between them; where they differ, plan for the worse option.

• Summit wind speed and direction, plus gusts.
• Temperature at height, and the wind chill it produces.
• Cloud base relative to your highest point.
• Precipitation totals and timing.
• Freezing level in winter, or any hint of ice.
• Daylight hours against your estimated pace.

Then turn the numbers into a plan: the route that suits the wind direction, an alternative at lower altitude, a turnaround time and a clear idea of what would make you turn back. Check again in the morning — forecasts shift overnight, especially the timing of rain — and be honest about what you find.

Conditions change, and so should your plan. Turning around because the wind has risen above what you expected, or because the cloud has come down early, isn't a failed day out. It's hillcraft, and it's the habit that keeps you walking in the hills for decades.