Summit Wind | topo^alpin

For mountain locations, surface wind (10 m) is of limited use. topo^alpin selects the appropriate pressure level based on the DEM elevation of the API grid point:

DEM Elevation	Wind Source
< 1200 m	Surface wind (10 m)
1200–1600 m	Blend 10 m ↔ 850 hPa
1600–2300 m	850 hPa (~1500 m)
2300–2800 m	Blend 850 hPa ↔ 700 hPa
> 2800 m	700 hPa (~3000 m)

Transition zones use linear interpolation. AROME provides no upper-level wind and falls back to 10 m.

Exposure Correction

For exposed locations, wind is additionally scaled:

Peak: factor 1.4
Saddle/Pass: factor 1.3

Wind Vector Averaging

Wind direction is not averaged arithmetically (that would give 180° for 350° and 10°), but via speed-weighted vector averaging:

$\bar{\theta} = \arctan2\!\left(\sum_i w_i \cdot v_i \cdot \sin\theta_i,\;\sum_i w_i \cdot v_i \cdot \cos\theta_i\right)$

Wind speed is the weighted average:

$\bar{v} = \frac{\sum_i w_i \cdot v_i}{\sum_i w_i}$

Gusts

Gusts are the absolute maximum across all hours in the block and all active models – not an average. Guard: gusts are never less than mean wind speed.

When a model provides no gusts (e.g. AIFS), the upper-level wind is scaled with an elevation-dependent factor:

DEM Elevation	Scaling Factor
< 1400 m	1.2
1400–2500 m	1.2–1.3 (linear)
2500–4000 m	1.3–1.45 (linear)