01 · The Fetch Principle
Fetch — the actual word — is the uninterrupted distance wind travels across open water before reaching a given point. It's a foundational concept in physical oceanography and the single biggest variable that determines surface conditions on any inland lake.
A north wind at 12 mph does completely different things to different parts of the same lake. The southwest cove with 400 meters of land-buffered exposure? Glass. The main channel with 3,200 meters of open water directly into that same wind? Whitecaps building. Same wind. Same moment. Completely opposite conditions.
Standard weather apps give you one number for the whole lake. That number isn't wrong — it's answering the wrong question. We answer: where, specifically, is the water clean right now?
Stylized bird's-eye view — same wind, different conditions by fetch exposure
02 · The Formula
Wind speed doesn't scale wave energy linearly — it squares. Double the wind and you get four times the wave-building energy. That relationship is captured in the core exposure equation applied to every point on every modeled lake.
Fetch distance is calculated geometrically per point — measuring unobstructed open water in the upwind direction against the actual shoreline. The result is a single energy value that drives the condition classification for that location.
Notice: same wind speed across all three scenarios. The variable is purely the geometry of the lake. That's why a single weather station can never tell you what you actually need to know.
03 · The Grid
Each lake is covered by a dense layer of scored points at consistent intervals across the entire water surface. Every point receives its own fetch calculation, depth lookup, and condition classification on each request. Morse runs 6,226 independently scored points.
Point spacing is calibrated to match real bathymetric data and resolve the pockets of protected water that matter. Fine enough to distinguish the inside of a cove from the land point next to it — coarser would miss the glass you're driving out to find.
No interpolation. No region averaging. Every point is independently scored against live wind on each call.
Stylized grid — each dot = one independently scored point
04 · Depth Context
Wave energy interacts with the lake floor. In shallow water — anything under about 8 feet — the bottom friction amplifies surface chop and causes waves to build steeper and break earlier. The same energy hitting a 20-foot channel produces rolling swells. The same energy in a 3-foot flat produces short, messy chop that's rough to ride in.
We layer in USGS bathymetric depth data at each grid point. The depth at each location modifies the exposure score with a multiplier: deep points get a slight reduction (cleaner than raw fetch suggests), shallow points get a bump (worse). This brings the map's predictions in line with what you actually find on the water.
The depth adjustment is a secondary modifier, not the primary variable — fetch geometry drives the classification. But it's the layer that brings the model's predictions in line with what you actually find on the water, especially in the shallower sections of a lake.
Lake cross-section · depth × wave behavior
05 · The Scoring System
Every scored point falls into one of five condition tiers based on its calculated exposure value. The session score (1–10) is derived from the weighted distribution across all points — heavily penalizing whitecap coverage and rewarding glass percentage.
When 60%+ of the lake is at glass level, you're looking at a send-it morning. When 40%+ is rough or worse, the map's job is to show you where the good water still is — not send you to the worst of it.
06 · Sport Modes
The base mode gives a general condition overview for the whole lake — the right starting point for any rider, useful both for planning and checking in while you're already out. Sport modes are the decision layer on top: same underlying model, sport-specific scoring logic. Tier boundaries shift. Depth sensitivity changes. What registers as "acceptable" is recalibrated to match how each discipline actually experiences the surface.
A wake surfer sitting inside the boat's wake cares primarily about depth clearance and corridor width, not ambient chop. A barefoot skier at 40 mph needs near-perfect glass — any texture translates directly to a fall. Same lake, same moment, completely different answers. That gap is real, and sport modes are how we close it.
07 · The Bottom Line
Three things happen when you use Fetch instead of checking the wind and guessing.
You know how it works. Now see it live.
Live on Morse Reservoir. More lakes coming. Free during beta.