How our mountain forecast works

Every Peakify mountain page is built from computer weather models, worked out for the summit's real height. This page lists the sources, how each verdict and score is calculated, and what the forecast can't tell you.

Where the data comes from

  • Open-Meteo

    Hourly and daily forecast for the summit, a mid-height point and the valley, with freezing level, UV, CAPE and dew point. It blends the best model for each place and hour.

  • ECMWF IFS, Met Office UKMO and DWD ICON

    Three separate models, read through Open-Meteo, compared side by side to show each day's range and confidence.

  • RainViewer

    Rain radar for the last two hours.

  • NOAA SWPC

    Aurora Kp index.

  • Mapbox and OpenStreetMap

    3D terrain and route maps. Map data © OpenStreetMap contributors.

  • Peakify route plans

    Route lines plotted by Peakify on the map and checked against the paths. Download them as GPX from each route.

Three heights, not one

Each mountain gets three forecasts: at the summit's surveyed height, at a point halfway up, and in the valley at the lowest nearby start. Models smooth hills into gentle bumps, so we ask for the forecast at the real summit height. That is why our summit wind and cold are often harsher than a town forecast a few miles away.

The summit verdict

Each day is rated Good, Marginal or Poor from the summit forecast, using these limits (rounded to the nearest whole number first):

  • Poor: mean wind 40 mph or more, or gusts 65 mph or more.
  • Marginal: mean wind 25 mph or more, gusts 45 mph or more, a 60% or higher chance of rain, a feels-like of −8°C or colder, or the cloud base below the summit.
  • Good: under all of those.

You can set your own gust, rain and feels-like limits on any mountain page; they are saved on your device only. From day 8 onwards, gusts above 75 mph and winds above 55 mph are shown as "75+" and "55+", because models overdo extremes that far ahead.

Cloud base and summit cloud

Cloud base is worked out from the valley's temperature and dew point: roughly 125 m of height for every degree between them. When the cloud base is below the summit, the summit is in cloud. "Summit clear of cloud" is the share of daylight hours with the cloud base above the top.

Forecast confidence

We compare three independent models (ECMWF, the Met Office's UKMO and Germany's ICON) for each day's strongest gust, highest temperature and total rain. When they agree closely, confidence is high. When gusts differ by 25 mph, temperatures by 5°C or rain by 10 mm, confidence drops, and it drops further the further ahead the day is. Each day shows the range across the three models.

Ground, kit and wind effects

The ground gauge uses the last 24 hours of rain, the day's forecast rain, snowfall and frost. The kit list follows the forecast: microspikes when the freezing level is below the summit, an ice axe and crampons in snow. Wind is described by its effect on a walker, from "little effect on walking" to "impossible to stand on exposed ground".

Dark sky and cloud inversions

The dark sky score takes each night's best two hours in a row and weights cloud (40%), the moon (20%), light pollution (15%), humidity (10%), full darkness (10%) and wind (5%). The cloud inversion score is explained on what is a cloud inversion.

What the forecast can't tell you

Models can't see local effects like funnelled wind on a ridge, ice on a shaded path, or a path closed for repairs. A verdict covers the summit weather only. Before you go, also read a forecast written by a person and the latest ground conditions: MWIS, the Met Office mountain forecast, and the national park's own reports. In an emergency in the UK, call 999 and ask for Police, then Mountain Rescue.

Questions

Is Peakify a Met Office forecast?

No. Peakify reads computer weather models through Open-Meteo, including the Met Office's own model, and works out summit verdicts from them automatically. No forecaster writes it. For a human-written forecast, read MWIS or the Met Office mountain forecast as well.

How often does the forecast update?

The summit forecast behind each mountain page is refreshed at least every hour. The page you see may be up to five minutes old.

Why does Peakify sometimes disagree with other sites?

Different sites use different models, heights and grid points. Peakify forecasts for the summit's real height, not the model's smoothed ground, which is why summit winds and temperatures can look harsher than a town forecast.