Low-Level Jet Phenomenon – The Hidden Nighttime Wind That Sets Up Dawn Patrol
Most riders sleep through the best wingfoil wind of the day. While you are in bed, a phenomenon called the Nocturnal Low-Level Jet (LLJ) is building speed just above the water.
This is the secret engine of the "Dawn Patrol." If you understand how it forms, you can score a glass-water session at 25 knots before the rest of the world wakes up.
The Decoupling Effect
During the day, the sun heats the ground. This creates turbulence. The air mixes. The friction of the earth slows down the wind speed.
At night, the ground cools rapidly. The air near the surface becomes stable and heavy. It stops mixing with the air above it. This is called "decoupling."
The air layer at 200 meters altitude is now free from surface friction. It becomes slick. It accelerates. Without the drag of the trees and waves, this "jet" of air can reach speeds of 40 to 50 knots, even if the surface wind is calm.
The Morning Mix-Down
Here is the trick for the wingfoiler. The LLJ is usually too high to ride at 4 AM. You need it to come down to the water.
This happens at sunrise. The sun hits the water. Weak thermals begin to rise. These thermals puncture the stable layer. They act like a spoon stirring coffee. They drag the high-speed momentum of the LLJ down to the surface.
For about 90 minutes after sunrise, you get a "burst" of high wind. The water surface is still flat because the wind has just touched down. It is the holy grail: 25+ knots of power on mirror-flat water.
Reading the Skew-T
You cannot see the LLJ on a standard icon forecast. You need a meteogram or a Skew-T chart.
Look at the wind speed at 900mb or 850mb (approx 1,000 to 1,500 meters). If the forecast shows 30 knots at that height but only 5 knots at the surface, an LLJ is likely forming.
The Collapse
The LLJ is a fragile beast. As the day warms up, the mixing becomes too strong. The jet energy dissipates into the general atmosphere. By 10 AM, the wind speed usually drops back to the standard forecast average.
Summary
Set your alarm. Check the ensemble forecast for high-altitude winds at night. If the wind gradient is extreme, get to the beach at sunrise. You will catch the mixing burst. It is the cleanest, fastest wingfoil wind you will ever ride.