In winter, Krakow is associated with two phenomena: smog and fog. Both reduce visibility, both appear on the same windless days, and both can look like a grey curtain over the city. For aviation, though, they are completely different things. Diversions from Balice are caused by fog, not smog — even though the two share a common origin.
Smog, fog, mist, haze — what is the difference?
In everyday language, anything that reduces visibility gets called "fog" or "smog". Aviation meteorology distinguishes several phenomena, each with its own code in weather reports:
| Phenomenon | What it consists of | Visibility | METAR code |
|---|---|---|---|
| Fog | Tiny water droplets or ice crystals | Below 1,000 m | FG (freezing: FZFG) |
| Mist | Water droplets at a lower concentration than in fog | 1,000 to 5,000 m | BR |
| Haze | Dry solid particles — dust, pollutants | Reported at 5,000 m or less | HZ |
| Smoke | Combustion products | Reported at 5,000 m or less | FU |
Smog is not a separate category in aviation reports. It is air pollution — a mixture of particulates and gases from human activity. Depending on humidity and particle concentration, it may appear in a report as haze (HZ) or smoke (FU), and in humid air it contributes to mist or fog.
A shared origin: inversion in the basin
Smog and fog so often occur together because they need similar conditions:
- No wind — the air is not exchanged, so pollutants and moisture stay near the ground.
- Temperature inversion — a layer of warmer air above cold air acts like a lid. It stops pollutants rising and encourages overnight cooling, which leads to water vapour condensing.
- High humidity and the cold season — around Krakow, most foggy days fall between October and January, which is also the heating season.
The terrain amplifies both. Krakow lies in the Vistula valley surrounded by hills, and a dense river network raises air humidity.
How pollution combines with fog
Fog forms when water vapour condenses on so-called condensation nuclei — tiny particles of dust, salt or pollutants. According to Poland's Institute of Meteorology and Water Management (IMGW), at very high concentrations solid particles can combine with water molecules into larger aggregates that noticeably reduce visibility. That is why, on smoggy and humid days, the line between pollution and mist becomes blurred.
Smog in the city, fog at the airport
Krakow-Balice Airport is not in the city centre but to the west of it, outside the city limits. It has its own unfavourable microclimate. It sits on the floor of the Krzeszowice Graben and the Rudawa valley, close to forests and peatland. Poor ventilation and large contrasts in temperature and humidity mean fog occurs there often and lingers longer than in the city itself.
In practice this means two things:
- High smog levels in central Krakow do not mean there is fog at Balice — and vice versa.
- Fog over the airport has mainly natural causes. Better air quality in the city, for example after Krakow banned burning coal and wood from 1 September 2019, does not remove the diversion problem.
We cover this in detail in Fog at Krakow Airport — causes and local conditions.
Can smog stop landings?
Smog on its own rarely reduces visibility enough to prevent landing. A CAT I ILS approach requires runway visual range (RVR) of at least 550 metres — far less than the haze typically caused by pollution. IMGW notes that smog could theoretically reduce visibility below minima, but in practice fog is what causes diversions at Balice.
Visibility from the ground vs from the cockpit
During an inversion, the smog layer sits low, beneath warmer air. A pilot flying above that layer may see clear skies and the surrounding area, while instruments on the ground measure much worse visibility. IMGW described such a case in Warsaw in 2017: the airport reported visibility of 1,700 metres while pilots near the city could see its centre. But landing decisions depend on measurements at the runway, not on what can be seen from above.
Comparison: smog and fog from a passenger's point of view
| Smog | Fog | |
|---|---|---|
| Nature | Air pollution (particulates, gases) | Weather phenomenon (water droplets) |
| Main source | Heating, transport, industry | Cooling and condensation of moisture near the ground |
| Typical visibility | Usually above 1,000 m | Below 1,000 m, sometimes a few dozen metres |
| Impact on landings | Usually none | Low visibility procedures, delays, diversions |
| Where to check | Air quality services (PM10, PM2.5) | Airport visibility and RVR |
Practical tips
- Do not judge your flight's chances by a smog app. A smog alert in Krakow says nothing about landing conditions at Balice.
- Look at visibility, not air quality. Check current visibility and RVR or Is there fog in Krakow?
- When reading the METAR for EPKK: HZ or FU usually pose no threat to operations, BR signals humid air and a risk of deterioration, and FG means fog and possible disruption.
- Mornings are most exposed in autumn and winter — around 60% of fog in the Krakow area occurs in the morning.
How the airport operates when visibility really drops is explained in Low visibility procedures at Krakow Airport.
Check the current situation
Quick answer: Krakow Airport fog today.
See also
- Fog at Krakow Airport — why Balice is so prone to it.
- Low visibility procedures — what happens at the airport in fog.
- Visibility at Krakow Airport — what RVR is.
- Best months to fly from Krakow — when fog risk is lowest.
- Aircraft de-icing in winter — the other winter cause of delays.
- Flight cancelled by weather — what you are entitled to.
FAQ
Does smog in Krakow affect flights?
Usually not. Smog alone rarely reduces visibility below landing minima, which for a CAT I ILS approach are 550 m RVR. Delays and diversions at Krakow-Balice Airport are caused in practice by fog, although smog and fog often occur in the same conditions.
What is the difference between smog and fog?
Fog is a weather phenomenon — suspended water droplets reducing visibility below 1,000 m. Smog is air pollution made up of particulates and gases from human activity. The two reinforce each other in windless weather with a temperature inversion.
What do FG, BR and HZ mean in a METAR report?
FG means fog with visibility below 1,000 m, BR means mist with visibility from 1,000 to 5,000 m, and HZ means haze caused by dry solid particles such as dust. FU means smoke. Smog has no separate code.
Why is there fog at Balice Airport but not in Krakow?
The airport lies outside the city, on the floor of the Krzeszowice Graben and the Rudawa valley, close to forests and peatland. Poor ventilation and large contrasts in temperature and humidity mean fog occurs there often and lingers longer than in central Krakow.
Did Krakow's coal-burning ban reduce the number of diversions?
There is no evidence for that. The ban in force since 1 September 2019 improved air quality in the city, but fog over the airport mainly has natural causes linked to terrain and humidity.
Why can a pilot see the ground while the airport reports poor visibility?
During a temperature inversion, a layer of smog or mist sits low near the ground. A pilot flying above it may see the surrounding area, while instruments at the runway measure much worse horizontal visibility. Landing depends on measurements at the airport.