The outdoor weather beside your charts

Give the account its place

The weather is chosen for the account's place, which is kept to a tenth of a degree - about 10 km - and never more precisely. An Admin sets it under Settings, Account Information:

• Use this browser's location (rounded to about 10 km). The browser asks you first, and rounds the position before it is sent.
• From Home Assistant: the Tag Historian integration, in its next release, has the option Use my approximate location (about 10 km) for outdoor weather from SMHI. It is off until you turn it on, and then proposes your Home Assistant's location, rounded the same way, while the account has no place.

Removing the place under Settings removes the weather with it, and Home Assistant does not propose it again; set a place there to have the weather back.

Which stations

Within a few seconds of setting the place - or within the hour, when SMHI is slow to answer - the account gets the nearest stations that have measured lately, chosen from SMHI's list of stations:

• within 50 km of the place, nearest first;
• SMHI's core network first; the additional stations, which SMHI checks less, only where no core station is within 30 km;
• among stations about as near, one with at least five years of history before a younger one;
• temperature and precipitation separately: the nearest rain gauge is often not the nearest thermometer.

Settings names each station and how far it is from the place. An Admin can pick another with Pick another station, from the active stations nearest the place. The first time any account uses a station, we fetch up to 10 years of its history, so a new chart has the weather of earlier years too.

On a chart

1. Open Trends with the tags you want to see.
2. Tick Weather. The temperature is drawn as a dashed red line against the chart's °C axis - or an axis of its own, °C outdoors, when no tag is in °C - and the precipitation as bars along the bottom of the chart, the wettest hour of the window as tall as the lane.
3. Hover over the chart: under it, the weather at that moment is written out beside the credit to SMHI.

Up to 31 days the weather is hourly; over a longer window each point is a day - its mean temperature, with its lowest and highest, and its precipitation added up - or several days on a window of years. The weather takes none of the chart's three unit axes and is not one of its ten tags. The address of the chart says weather=1, so a bookmark or a link to it opens with the weather on.

What an hour of weather is

• Temperature is SMHI's reading at the start of the hour, the value the hour began with.
• Precipitation is what fell during the hour, in mm. SMHI gives it at the end of the hour; we place it on the hour it fell in.

Both are placed on whole UTC hours. Trends draws in your browser's time, so in Sweden an hour of weather starts on the hour there too.

How fresh it is

We fetch SMHI's latest hour every hour, and a chart shows it as soon as it is in - SMHI's own latest values, which SMHI still checks. The day is stored at 04:00 UTC the next morning, once the hours SMHI publishes late are in. Once a week any hour still missing is fetched from SMHI's last four months, and once a month the values SMHI has since corrected replace ours. The weather is kept for 10 years.

If a station stops sending for two days while SMHI's other stations are fine, the account is moved to the next best station for its place, and the switch is noted on the account's timeline. While SMHI as a whole is not answering, nothing is switched: the chart has a gap, which is filled afterwards.

Export the weather

The weather can be saved as CSV through the API, with a key that may read measurements:

• GET /api/export/series?ref=weather:temperature&from=2026-10-01T00:00:00Z&to=2026-11-01T00:00:00Z - a row per hour, up to 93 days;
• ref=weather:precipitation&interval=day - a row per day in the account's time zone (timeZone to choose another), up to ten years, cut where the meters' increase per day is cut.

Every row names its station and carries SMHI's credit. GET /api/weather/series answers a chart's window with both, and GET /api/weather/stations lists the stations near a place.

SMHI's licence

SMHI publishes its observations as open data under Creative Commons Attribution 4.0 (CC BY 4.0 SE). It asks that SMHI is named as the source and that any change is said. Everywhere we show or export the weather we say: Source: SMHI (CC BY 4.0), station X, values placed on the UTC hour. If you publish a chart or a file with the weather in it, keep that line with it.