The Basic Rule
Wind is air moving from high pressure to low pressure. The bigger the pressure difference between two zones, the faster the wind accelerates.
This pressure difference is called the pressure gradient, and it's the fundamental driver of all wind.
Why Wind Exists
Air constantly tries to equalize pressure. When the sun heats one area more than another, pressure differences form. Air accelerates from high to low pressure zones to restore balance.
Stronger gradient = faster acceleration = higher wind speed
What Is a Gradient
A gradient measures the rate of change over distance:
- Steep gradient: Pressure drops sharply over short distance → Strong wind
- Shallow gradient: Pressure drops slowly over long distance → Light wind
- No gradient: Pressure is uniform → No wind (calm)
Think of it like a hill: steep slopes make you accelerate faster when rolling down.
Reading Isobar Maps
Weather maps show pressure using isobars—lines connecting points of equal pressure. The spacing between these lines reveals wind speed:
Isobar Spacing Guide
Wide spacing (4+ mb per 100km)
Light
Shallow gradient → 0-10 knots. Calm to light breeze.
Moderate spacing (2-4 mb per 100km)
Moderate
Medium gradient → 10-20 knots. Good foiling wind.
Tight spacing (1-2 mb per 100km)
Strong
Steep gradient → 20-30 knots. Powered conditions.
Very tight spacing (<1 mb per 100km)
Storm
Extreme gradient → 30-50+ knots. Dangerous winds.
High vs Low Pressure Systems
Understanding pressure system structure helps predict wind:
- High pressure (H): Air sinks, flows outward. Generally calm at center, wind on edges.
- Low pressure (L): Air rises, flows inward. Strongest winds circle the low.
- Between systems: Maximum gradient = maximum wind
Wind flows perpendicular to isobars (parallel to pressure gradient), curving due to Earth's rotation (Coriolis effect).
Practical Forecast Reading
When checking forecasts, look beyond just the wind number:
Gradient Analysis Tips
Count isobar lines: More lines = tighter gradient = stronger wind
Check line spacing: Tighter spacing = accelerating wind
Track low pressure centers: Strongest winds orbit the low
Widening isobars = weakening wind: Gradient relaxing
Converging isobars = building wind: Gradient strengthening
Summary
Wind comes from pressure differences. The tighter the gradient (closer the isobars), the stronger the wind you'll feel. Learn to read isobar maps to understand not just current wind, but how wind will evolve over the next 12-24 hours.