How to Read a Weather Forecast (and What the Numbers Mean)

A weather forecast packs a lot into a few numbers and icons. Knowing what each one means — and how much to trust it — turns a forecast from a guess into a useful plan. Here is a quick decoder.

Chance of rain (probability of precipitation)

The percentage you see is the probability of precipitation — how confident the forecast is that measurable rain (or snow) will fall during that period. "70% chance of rain" means rain is likely; "20%" means it is possible but unlikely. It is not a measure of how hard it will rain or for how long. For that, look at separate figures like expected rainfall in millimetres, or the conditions icon.

Temperature vs "feels-like"

The plain temperature is the air temperature in the shade. The feels-like (or apparent) temperature adjusts for what your body actually experiences:

• When it is cold and windy, wind chill makes it feel colder than the thermometer, because moving air strips heat from your skin faster.
• When it is hot and humid, the heat index makes it feel warmer, because high humidity stops sweat from evaporating and cooling you.

If you are dressing for the day, the feels-like number is usually the more useful one.

Humidity, wind and pressure

• Humidity is how much water vapour is in the air, as a percentage of the maximum it could hold at that temperature. High humidity makes heat feel worse and can signal muggy, sticky conditions.
• Wind is given as a speed and often a direction (where it blows from). Gusts can be much stronger than the steady wind, so check both if you are cycling, sailing or flying a drone.
• Pressure trends matter more than the absolute value: falling pressure often means unsettled or stormy weather is coming, while rising pressure usually means clearer, calmer conditions.

Why a 7-day forecast gets fuzzier toward the end

Weather is a chaotic system: small errors in today’s measurements grow quickly, so certainty drops the further ahead you look. The next one to two days are usually very reliable. By day six or seven, treat the forecast as the general trend — "warming up", "a wet spell mid-week" — rather than an exact promise. Checking the forecast again the day before still beats relying on a week-old outlook.

Put it together

Read the icon for the overall picture, the feels-like for how to dress, the chance of rain for whether to carry an umbrella, and the wind if you will be outdoors. Then trust the near term more than the far term.

See all of these for your own location — current conditions plus a 7-day outlook in °C or °F — with the Weather Forecast tool. Pair it with the Sun Times tool to know how much daylight you have to work with.