Weather Forecast Guide

This guide provides information on the icons used in the forecasts, as well as explaining some of the mode in-depth features.

Layout

Choose from different forecast layouts: view hour by hour forecasts in Classic or Timeline, or 16 day forecasts in Classic, Table, or Timeline.

The Timeline view is especially useful for tracking expected changes in weather throughout the day.

Timeline forecast

Rain and precipitation

Forecast rain totals for the given time period are shown in mm.

The chance of rain is given on some forecasts as a percentage. It is calculated by analyzing the forecasts over a grid surrounding your location. The area of the grid is dynamically changed to increase confidence, based on the model being used and the time of year.

For example, if the chance of rain is 50%, it means that rain is forecast for 50% of the grid points surrounding your location.

The thunderstorm risk is based on the Convective Available Potential Energy (CAPE) forecast for your selected location.

Snow forecasts are based on the precipitation type variable provided by computer models. In some cases, additional processing is done that factors in dew points and temperatures.

Wind

Wind direction, mean wind speed and gust wind speed forecasts are provided.

Wind direction is in degrees. By default, mean wind speed and gust wind speed are displayed in mph, but km/h and kts are available from the unit selector.

Temperature

Temperature forecasts by default are displayed in Celcius, but Fahreinheit can be chosen from the units selector.

Typically, nighttime values use the minimum temperature variable (where available) from the computer model, while daytime values use the maximum temperature variable (where available).

A value for "feels like" (sometimes called wind chill) is displayed on some of the forecasts. This refers to how cold the air feels on your skin due to the combination of air temperature and wind speed.

850hPa temperatures

Temperatures at the 850hPa level are useful to help determine the risk of weather types, particularly snow in the winter and heat in the summer. The 850hPa level is approximately 1500 meters above sea level.

hPa: Stands for hectopascal, a unit of atmospheric pressure. One hectopascal is equal to 100 pascals.

Thickness

Thickness values refer to the vertical distance between two pressure levels in the atmosphere. In this case, we are considering the thickness between the 1000 hPa (near the surface) and 500 hPa (roughly 5.5 kilometers or 3.4 miles above sea level) pressure levels.

Higher Thickness: Indicates warmer air. Values of 564 decameters (dam) or higher are often associated with heatwave conditions in the summer months.

Lower Thickness: Indicates colder air. Values of 528 dam or lower are considered a marker for the possibility of snow.

Decameter (dam): A unit of length in the International System of Units (SI), equal to ten meters.

UV index

The UV index is a measure of the strength of the sun's ultraviolet (UV) radiation at a particular place and time.

The UV index scale typically ranges from 0 (low) to 11+ (extreme). The higher the number, the stronger the UV radiation, and the greater the risk of sunburn and skin damage.

It is important to take precautions to protect yourself from the sun when the UV index is 3 or higher.

The maximum expected UV index for the day is displayed on the 16 day forecasts for the first 4 or 5 days of the period.

Cloud Base Height (CBH)

The cloud base height (CBH) is the altitude at which clouds are expected to form. It is an important parameter for aviation, weather forecasting and outdoor activities.

CBH values are meters above ground level. Lower cloud bases are associated with poorer visibility and higher fog risk, while higher cloud bases indicate clearer conditions.

CBH is currently displayed on the UK hourly forecasts when you set the model data to UKV.

Icons

The icons show the predominant weather type at the given forecast time.

18°C Temp	Wind direction	Sun / Clear	Sun / Clear periods	Sun / Clear intervals
Cloudy	Light rain	Heavy rain	Showers	Thunder
Sleet	Snow showers	Light snow	Heavy snow

Guidance

This is designed to add context to the weather forecast. For example, if rain rates are forecast to exceed a defined level, a notification warning about the possibility of dangerous driving conditions is given.

Will it, MOGREPS-G and GEFS forecasts

These provide data from ensemble models, which show the likelihood of different outcomes.

Probability forecasts offer a more realistic picture of the weather outlook beyond a few days by expressing the likelihood of different outcomes. Instead of a single deterministic forecast (e.g., "sunny"), you might see probabilities for different conditions (e.g., "60% chance of rain, 40% chance of clouds").

Celestial information

The Celestial Information section provides useful details about the sun and moon specific to your forecast location. Here's a quick guide to what each item means:

Note: All times are approximate and based on rounded location coordinates, so variations may occur.

Sun Information

• ▲ / ▼ Times: Sunrise and sunset times.
• Solar Noon: The time when the sun reaches its highest point in the sky.
• Dawn / Dusk: Times when different levels of twilight occur:
  • C (Civil): Enough natural light for most outdoor activities.
  • N (Nautical): The horizon is still visible at sea.
  • A (Astronomical): The sky is dark enough for astronomy.
• Golden Hour: Periods shortly after sunrise and before sunset when the light is soft and warm—ideal for photography.
• Solar Position at Noon: Indicates the altitude (height in the sky) and azimuth (direction along the horizon) of the sun.

Moon Information

• ▲ / ▼ Times: Moonrise and moonset times. If "n/a" is shown, the moon does not rise or set on that date at your location.
• Moon Phase: Current phase of the moon (e.g., Waning Gibbous, New Moon).
• Moon Position at Noon: The moon's altitude and azimuth at midday.

This data helps you plan everything from stargazing and photography to outdoor events and daily routines based on natural light.