Fog in Romania: winters have about half the foggy days they had in the 1970s and ’80s

#The map: how much each station lost

Each circle is a station. The open ring shows the average winter in 1973–1989, the filled disc the average winter in 2015–2025. Tap a station to see its November mornings in the window above.

#Where the fog stayed: Petroșani, Zalău, Miercurea Ciuc

Three stations barely lost any fog. At Petroșani it rose, from 18.4 to 35.6 days a winter, though the old series has only 5 complete winters. At Zalău it stayed about the same (16 then, 17.4 now), also from few old winters. At Miercurea Ciuc, the foggiest station today, it fell a little: from 54.7 to 51.1.

At Miercurea Ciuc, November is even foggier than it was: 11.8 days, against 10.9. Petroșani and Miercurea Ciuc sit in basins closed in by mountains, where cold air collects on calm nights. At many stations on the plains and by the sea the fall is large: at Drobeta-Turnu Severin, from 58.7 to 10.9 days; at Constanța, from 42.7 to 11.8 (the extreme cases may also reflect a station move).

#Last winter was foggy. Up to 7 November 2026, not

In November 2025 the median station had 9 foggy days (29 stations), the foggiest November since 2012, compared on the same stations. December 2025 had 11 foggy days at the median station, more than a typical December in the 1970s–80s (9.5). The fog has not gone: it comes less often, with good years and bad ones.

Between 1 and 7 November 2026, none of the 20 stations with data had more than one foggy day. This year’s mornings are in the window too: choose “November 2026” under “A November now”.

#Method

The main source is the hourly observations of Romanian weather stations as kept by NOAA’s Integrated Surface Database (1973–2024), completed with GHCNh (2024–2026) and the original SYNOP messages on Ogimet (November 2024–2026). Only the synoptic hours (00, 03, …, 21 UTC) are used, the same in every period.

A month counts if at least 60% of its days have six or more readings. A station enters the comparison if it has at least four complete months (or winters) in 1973–1989 and four in 2015–2025. The result was checked four ways: requiring all eight readings, using only 00/06/12/18 or only 03/09/15/21 UTC, and dropping readings taken in rain or snow. The median ratio between periods stays between 0.43 and 0.52 at the stations with winters measured in 1973–1987.

Between 2014 and 2023 the archive keeps most visibilities under one kilometre in coarse steps (50, 200, 500 metres), so a morning shown at 500 m may have been anywhere from 500 to 999 m. The steps do not move the one-kilometre line: for four test months the count of foggy days matches the original messages exactly. The fall also shows in airport reports (METAR), a separate stream: at 14 of 15 airports, winters in 2015–2024 had less fog than in 1995–2014, by about a fifth on average. An independent study of the Romanian meteorological service’s own records (56 stations, 1981–2017; Hůnová and colleagues, 2021) also found a significant decrease in the probability of fog.

Limits: between 1999 and 2013 the archive holds only 17–20 of the 34 stations, and its coordinates do not record station moves, so any one station’s figure may include a move. The national result does not depend on any single station. The morning visibility is the 06 UTC reading (8 am in winter); when it is missing, the 03 UTC reading, then the 09 UTC one.