How barometer.today builds its animated global isobar maps using open weather data

Barometer.today, a web tool showing air pressure forecasts for cities worldwide, also features an animated global isobar map spanning one day back to four days ahead. The map is generated from ECMWF forecast data sourced via Open-Meteo, delivered as a pressure grid at 0.25-degree resolution and updated four times daily. To prevent jagged contour lines, the team applies a Gaussian blur, but uses a normalized convolution technique to stop inflated sea-level pressure values over high plateaus — such as the Himalayas and the Andes — from distorting surrounding data. Elevated terrain above 2,500 metres is masked using a digital elevation model, and isobars crossing these regions are rendered as dashed lines rather than omitted, keeping the map visually continuous while signalling extrapolated values. The underlying code is written in Python using numpy, scipy, contourpy, and shapely, and the approach is applicable to anyone drawing contour maps from gridded geospatial data.