The wind of Lago di Santa Croce: the Fadalto thermal explained with data
An analysis by NPHYSIS SRL based on 14,000 hours of measurements (2024–2026) and on the scientific literature about valley winds.
The lake and the saddle
Lago di Santa Croce (386 m, 7.2 km²) lies at the bottom of the Alpago basin, in the province of Belluno, closed to the north and east by the Alpago mountains and to the south-west by Col Visentin. Its connection with the Veneto plain is the Fadalto saddle, a low and narrow gap that descends towards the Val Lapisina, Lago Morto and Vittorio Veneto. This geography explains almost everything about the wind: the lake is the exit door of a corridor that starts in the plain.
How the thermal forms
On clear days the plain and the sunlit slopes warm up faster than the air sitting over the lake and on the basin floor. The air column of the valley and of the basin warms as a whole more than the one over the plain at the same altitude (the so-called volume effect of valley-wind theory), and a pressure difference builds that pushes air from the plain towards the basin along the Val Lapisina. The Fadalto saddle narrows the passage and accelerates the flow, like a gorge: this is why the wind reaches the lake from the south-south-west (220°) and is stronger at the mouth of the saddle than at the far end of the lake.
References: C. D. Whiteman, Mountain Meteorology (2000); D. Zardi and C. D. Whiteman, Diurnal Mountain Wind Systems (2013); S. Gaberšek and D. Durran, Gap flows through idealized topography (2004).
A typical day
| Local time | Hourly mean (kt) |
|---|---|
| 06:00 | 0.7 |
| 08:00 | 0.7 |
| 10:00 | 1.3 |
| 11:00 | 2.6 |
| 12:00 | 4.9 |
| 13:00 | 7.1 |
| 14:00 | 8.3 |
| 15:00 | 8.3 |
| 16:00 | 8.0 |
| 17:00 | 7.0 |
| 18:00 | 5.5 |
| 19:00 | 3.3 |
| 20:00 | 1.6 |
| 22:00 | 0.8 |
Calm until 09:00–10:00, onset between 11:00 and 14:00, plateau between 13:00 and 16:00, shutdown between 19:00 and 20:00. On the best days the peak falls between 13:00 and 16:00 (74 % of cases). An overcast morning delays the onset; if the sky opens at midday the wind comes in during the early afternoon.
The seasons
| Month | Hours ≥ 8 kt |
|---|---|
| February | 232 |
| March | 213 |
| April | 404 |
| May | 329 |
| June | 336 |
| July | 158 |
| August | 172 |
| September | 33 |
| October | 86 |
| November | 1 |
December and January: patchy data, usable days are rare.
The season already starts in late February (28 February 2026: 18.8 kt average from 224° at 0 °C) and peaks in April; July and August are weaker, September and autumn are almost still apart from synoptic episodes.
How much wind, really
At the shore station good days measure 7–12 kt of hourly average with gusts of 12–20; the best ones 15–20 kt average with gusts of 20–29 (the three 6 Aprils of 2024, 2025 and 2026 are among the strongest days in the series). The ratio between peak gust and hourly average is 1.58 (median over 666 windy hours).
Two things to keep in mind: the station, where it is mounted, reads less than the wind on the water, and the hourly average is lower than the 10-minute feel a kiter has out there. The «15–25 knots» quoted for the lake are gusts on the water, not hourly averages on shore.
The other winds
- South-south-westerly synoptic flow: when it blows strongly from S/SW aloft (approaching fronts, warm advection), the Fadalto channels it onto the lake at any hour, even at night or in the rain: 18 March 2025, 17.3 kt average at 1 a.m.; 5 October 2025, 19.7 kt with 18 mm of rain.
- Bora from the north-east: in situations with high pressure to the north-east, flagged by pressure at Maribor lower than at Trieste by more than 4 hPa. It is rare at the shore station.
- North-westerly synoptic flow after fronts, gusty, coming from the Belluno basin.
- Thunderstorms: sudden gusts and unpredictable directions; they are a danger, never a wind window (13 July 2019: a 41 kt gust recorded during a downburst).
- Night-time drainage: at Lago Morto, NE at 10–19 kt between 03:00 and 09:00, with calm on the lake.
What the models see
Global models at 13 km (those behind generalist sites) do not resolve a 7 km² basin and a saddle a few hundred metres wide. Models at 1–2 km (ICON-D2, AROME) partly see the circulation: on Sunday 6 September 2026 ICON-D2 had forecast 6.2 / 6.7 / 7.0 kt at 14:00, 15:00 and 16:00 in the lake cell, against 7.3 / 7.2 / 7.1 measured. Meteo Santa Croce uses five models, a thermal onset index built on the circulation the models do resolve in the Fadalto, and verifies its forecasts against the station every night.
Glossary
- Thermal (daytime valley wind)
- Gap flow
- Drainage (night-time katabatic wind)
- Bora
- Synoptic
- Hourly mean and gust
- Regimes R0–R6 (calm, thermal, Bora, NW synoptic, unsettled, thunderstorms, southerly synoptic)