Fog & inversion
CSENWill there be fog in the morning?
Out of season. Radiation fog and inversions belong to October through January; for now the page just shows what the measurements say.
When and where
- 3:00Jablonec nad Nisou
- 4:00Karlovy Vary
- 5:00MostLiberec
- 6:00Mladá BoleslavČeská LípaHavířovKladnoChomutov
- 7:00PlzeňOlomoucHradec KrálovéTepliceTábor
- 8:00Třinec
The rest
Praha, Brno, Ostrava, České Budějovice, Pardubice, Ústí nad Labem, Zlín, Opava, Frýdek-Místek, Karviná, Jihlava, Děčín, Prostějov, Přerov, Třebíč, Znojmo
An indicative estimate, not a fog forecast. It comes from the temperature-to-dew-point gap, wind speed and cloud cover — the conditions under which radiation fog forms. Real fog also depends on terrain, nearby water and soil moisture, none of which are in the estimate.
Temperature inversion
The summits are 9.4 °C colder than the lowlands — ordinary stratification. Inversions usually arrive with calm high pressure in autumn and winter.
- 12.7 °C
- Summits (above 800 m)
- 22.1 °C
- Lowlands (below 400 m)
Measured at 6 summit and 18 lowland ČHMÚ stations. Churáňov: 16.1 °C.
See it from the summit camera— Churáňov (SV)FAQ
How reliable is the fog estimate?
It is an indicative estimate, not a fog forecast. It reads the conditions under which radiation fog forms — a small gap between temperature and dew point, light wind and a clear night. It does not know about terrain, nearby water or soil moisture, so valleys and lakesides get fog more often than the estimate suggests.
What is a temperature inversion?
Temperature normally falls with height. In an inversion it does the opposite: cold air pools in the basins with a warmer layer above it. Fog and low cloud then sit in the valleys all day while the summits stay clear. This half is not estimated — it compares temperatures actually measured at ČHMÚ summit and lowland stations.
Why the 03:00–09:00 window?
Radiation fog forms towards dawn, when the ground has radiated away the most heat and the air cools to its dew point. It usually burns off within a couple of hours of sunrise, so the window sits around first light.
Where does the data come from?
Forecast variables (temperature, dew point, wind, cloud) from a model via Open-Meteo. The inversion temperatures come from ČHMÚ open data — professional stations including Sněžka, Šerák, Lysá hora and Milešovka.