Weather Distribution

Weather Distribution

Overview

The Weather Distribution KPI shows the relative frequency of different weather conditions — sunny days, rain, fog, snow, thunderstorms, and more — as a percentage breakdown for a given year and season. It answers the question: "What is the typical weather mix at this site?"

Data comes from Open-Meteo historical ERA5 reanalysis, which provides daily WMO weather codes going back to 1940. Each code is classified into one of 12 broad categories (e.g., Clear, Rain, Snow, Thunderstorms/Tornadoes), and the platform calculates how many days of the year fall into each category.

This is a visualization-only metric — there is no A--E quality grade. The output is purely descriptive: it tells you the weather character of a site, which provides context for interpreting other KPIs such as warming stripes, temperature trends, and aridity.

The indicator is available only for past years (historical data). Users with edit permissions can generate data on demand for any year in the last 30 years.

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Calculation Methodology

Each daily WMO weather code is classified into one of 12 named categories using the full WMO 4677 classification table:

For each period (full year, spring, summer, autumn, winter), the percentage is calculated as:

$$\text{Percentage} = \frac{\text{Days in category}}{\text{Total days in period}} \times 100$$

Season boundaries are hemisphere-aware: southern hemisphere sites use inverted definitions (e.g., spring = September--November instead of March--May).

Data are sourced from Open-Meteo Historical Weather ERA5 at approximately 10 km daily resolution, covering 1940 to present.

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What You See on the Platform

Assessment > Microclimate > "Weather Distribution" (Doughnut Chart)

Doughnut Chart. A thin-ring doughnut chart (cutout 80 %, 180 x 180 px) showing the proportional breakdown of weather categories for the selected year and period.

Purpose: To show at a glance what fraction of days in a given year or season were clear, rainy, foggy, snowy, or stormy at this site.

Description: The chart card shows the title "Weather Distribution" with a cloud icon and E1 topic badge. Above the doughnut, a "Site" label confirms the data is for the monitored site (there is no Control Area comparison for this KPI -- weather is point-based). Two filter controls appear below the header: a Year selector dropdown and a Period filter with five options (Full Year, Spring, Summer, Autumn, Winter). The doughnut ring is divided into colored segments, one per weather category present in the data. Categories with 0 % are hidden from both the chart and the legend. On hover, a tooltip shows the category name and its percentage (e.g., "Clear: 42.3 %"). A commentary button allows adding qualitative notes. A download button enables PNG and CSV export.

Weather Distribution
Clear (42%)
Rain (19%)
Mist/Smoke/Dust (12%)
Snow (9%)
Fog (7%)
Wind (6%)
Drizzle (5%)

How it's calculated: Each segment's arc length is proportional to the percentage of days in that category for the selected year and period. Data is sorted descending by percentage before rendering, so the largest segment always appears first.

Legend: Each category is shown with a colored circle and its label. The 13 hardcoded category colors are:

There is no A--E quality scale for this KPI.

Interpretation example:

If the doughnut for Full Year 2024 shows Clear at 42.3 % (a large gold arc), Rain at 18.7 %, and Mist/Smoke at 12.1 %, this means the site experiences predominantly fair weather, with roughly one day in five bringing rain -- a typical temperate continental climate signature.

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