Observation vs forecast

Temperaturkollen shows only measurements. No value on the site is a forecast or a model calculation. This guide explains the difference, and why the temperature here can differ from the one in a weather app without either being wrong.

An observation

SMHI describes an observation as a value measured by an instrument and recorded, for example by a thermometer in a screen. A thermometer measures only the temperature close to the instrument. Weather stations are limited in number, mainly for economic reasons, so most Swedish towns have no measurements of their own.

A calculated value

To give values for many more places, SMHI combines observations with models. Its Mesan analysis, in operation since 1999, calculates values every hour on a grid of 2.5 × 2.5 km squares over parts of northern Europe, using observations and weather forecasts. SMHI is clear that these values are not direct observations.

A Mesan value represents the average over a whole grid square, and it is influenced by surrounding observations. According to SMHI, model-based series therefore vary less than series of real measurements, which are more sensitive to local conditions. For a given coordinate, a model value can be taken from the nearest grid square or interpolated from several surrounding ones.

A forecast

SMHI's forecast temperature is the expected air temperature two metres above the ground. For a single time one temperature is given; for a longer period two are given, the lowest and the highest. Forecasts are built from observations processed by models and meteorologists, and SMHI notes that they cannot always be completely right.

What "right now" means here

The "right now" value is the latest hourly value from a station: a momentary reading, not a mean. It is chosen like this:

• If the place's history station has an hourly value at most 180 minutes old, that value is shown.
• Otherwise we use the nearest station within 50 km that has such a fresh value, and name it with its distance.
• If no station qualifies, the last known value is shown and clearly marked as out of date. An old value is never presented as current.

The history and the "right now" value can therefore come from different stations. When they do, it is always written out.

Why there are no forecasts here

Temperaturkollen exists to compare what has actually happened: this year against another year and against the normal. Mixing an expected value into a series of measured ones would blur exactly that comparison. For a forecast, go to SMHI or another forecast service; for what the thermometer showed, come here.

A weather app often shows a model value for your exact position, while this site shows what a specific thermometer measured. On a calm, clear night the two can differ noticeably.