Reading Weather Forecasts for Hill and Coast

Why the hills and coast play by different rules

A forecast for the nearest town is a starting point, not a promise. On Exmoor, the Lake District or the Scottish Highlands, the summit can be five to eight degrees colder than the valley, with wind speeds double what you feel in the car park. On the coast, a sea breeze can turn a still morning into a blustery afternoon, and onshore winds push spray and big waves onto paths that looked benign at low tide. Always look for a dedicated hill or coastal forecast rather than a generic town one. If you are heading above 600 metres, assume the weather will be worse than the lower ground: wetter, windier and claggier.

Wind: the factor that catches people out

Wind is the most common reason walks turn miserable or dangerous. Forecasts give an average speed and a gust speed. The gust is what matters on exposed ridges and cliff tops. A steady 20 mph is manageable; gusts of 40 mph can knock you off balance, especially with a rucksack. On the coast, an onshore 30 mph wind brings salt spray, reduced visibility and waves that can sweep across a sea wall or causeway. Check the wind direction, too. A south-westerly might push you along an east-facing path, but the return leg will be a hard grind. Use the Beaufort scale as a rough guide: force 4 (13–18 mph) is a pleasant breeze; force 6 (25–31 mph) makes conversation difficult; force 8 (39–46 mph) is time to choose a low-level route.

• Look at the gust figure, not just the average.
• Note the wind direction and how it interacts with your route's aspect.
• Add wind chill to your clothing choices — it can feel 10°C colder on an exposed top.

Rain, showers and what the numbers really mean

Rain forecasts can be confusing. A 30% chance of rain means there is a three in ten likelihood of rain at that place and time — it does not tell you how much. Rainfall amount is given in millimetres: under 2 mm is light drizzle, 5–10 mm is a steady soaking, and over 20 mm in a day means saturated ground and swollen streams. Showers are hit-and-miss; you might stay dry while the next valley gets drenched. Frontal rain is more widespread and persistent. Also consider what fell yesterday. If the ground is already sodden, today's light rain will make paths, peat bogs and rocky slabs treacherous. Check the rainfall radar before you leave, but do not treat it as gospel.

Visibility, cloud and sea fret

Visibility is the quiet hazard. Hill fog can reduce views to 50 metres or less, turning a familiar ridge into a navigation exercise. Forecasts often give a cloud base: if it is 600 metres and your route tops out at 900 metres, you will be in the cloud. On the coast, sea fret — a cold, damp fog formed when warm air passes over cold sea — is common in spring and early summer, especially on north-eastern coasts. It can appear within minutes and hide cliff edges, breaking waves and path junctions. Inshore waters forecasts give visibility in metres or nautical miles; take note. If visibility is poor, rely on map, compass and GPS, and consider a lower, more sheltered route.

Temperature, timing and the last-minute check

Air temperature is only part of the story. Wind chill and wet clothing can rapidly lead to hypothermia, even in summer. Check the "feels like" temperature and plan for a 10°C drop on exposed tops. Time your walk to avoid afternoon thunderstorms in summer or early darkness in winter. Look at the forecast the evening before, then again at breakfast. A front arriving two hours earlier than predicted can change everything. If the wind is stronger, the cloud lower or the rain heavier than you expected, be ready to switch to a valley or woodland route. On the coast, always check tide times alongside the weather — a rising tide and an onshore wind can trap you against cliffs.

Turning a forecast into a decision

Before you set out, write down three or four key numbers: maximum gust, total rainfall, cloud base and visibility. Set personal thresholds. For example: gusts above 35 mph means no exposed ridge; cloud base below 500 metres means a low-level route or a navigation-focused day; visibility under 200 metres means a route you know well or cancel. Cross-check two forecast sources if you can, and be honest about your group's experience and fitness. Weather is not an excuse to cancel every walk, but it is a reason to choose the right one. Carry waterproofs, spare warm layers, a map and compass regardless of the forecast. The best days out are the ones where you read the sky as well as the screen, and you come home with stories rather than regrets.