Pressure layer

Atmospheric pressure as it actually flows around the planet — isobar contour lines plus L/H markers at the centers of low- and high-pressure systems.

What you see

  • Isobars. Curved contour lines drawn at fixed pressure intervals (typically 4 hPa). Tightly-packed isobars mean strong pressure gradients — strong winds. Widely-spaced isobars mean calm.
  • L / H markers. A blue L at every local minimum (a low — unsettled, often stormy weather), a gold H at every local maximum (a high — usually clear and dry). The number underneath is the pressure in hPa.
  • Pressure pills. Small chips scattered across the map showing the actual hPa value at that grid cell, so you can read absolute values without measuring isobar lines.

Why it matters

Pressure is the underlying engine of every other weather layer. Lows pull warm moist air upward (rain, wind). Highs press it back down (clear skies, calm). Reading the pressure map is the closest thing to seeing tomorrow's weather before it happens.

For trip planning:

  • A deep L slowly approaching from the west = brace for rain in 24–48 hours.
  • A persistent H over the route = high probability of stable weather for the next few days.
  • Closely-spaced isobars over your route = wind, regardless of what the wind layer shows right now.

How the contours are drawn

The raw pressure grid is bilinearly upsampled by 4× to 24× depending on zoom level (close zooms need more samples for smooth curves), then Gaussian-blurred to remove numerical micro-noise that would create unrealistic kinks in the lines. Standard meteorological practice.

Where the data comes from

Open-Meteo's global forecast grid (mean-sea-level pressure), refreshed every 30 minutes. Same source as wind and temperature.

Toggling on

Live map → top-right weather toggle → Pressure.

  • Wind — pressure gradients drive these.
  • Temperature — temperature differentials drive pressure systems.
  • Rain — most precipitation forms inside L's.

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