Meteorology and Hydrology
Meteorology and hydrology checks that you can read wind, weather and water levels and turn the forecast into a decision about today's passage.
Weather
- Beaufort force 5 already means about 8 m/s and significant wash; force 6–7 on open water such as Balaton can stop small craft.
- Fog forms when air cools to the dew point and is common on the Danube at dawn in autumn. In fog: reduce speed so you can stop within the visible distance, sound signals, radar watch, and moor if you cannot see the bank.
- Thunderstorms bring gust fronts; a sudden 20-knot shift can pin a vessel to a bank.
- Sources: national met service forecasts, Notices to Skippers, river level forecasts, your barometer and cloud observation.
Hydrology
- Gauges read above a reference level (RHM). Low water reduces depth and underkeel clearance and exposes shoals at groynes; high water increases current, reduces bridge clearance and triggers speed and wash restrictions.
- Flood stages bring official alerts, closure of side channels and eventually closure of the fairway; ice in severe cold can stop navigation.
- Current on a bend sets across the channel; eddies form behind groynes and bridge piers.
Worked example
The gauge on your section has risen 90 cm in 24 h, a further 40 cm is forecast, and the local order closes navigation above a set level. Your bridge clearance margin today is 0.25 m. Decision: do not pass the bridge; take the nearest sheltered harbour, double up moorings for the rising current, and keep listening to Notices to Skippers.
Traps
Planning on the forecast instead of the observed gauge; underestimating stopping distance in a 6 km/h current; assuming fog will lift before you reach the bridge; ignoring wind on a light, high-sided vessel.