A yellow fog warning means people should remain watchful and keep up with updated official information. It is a preparedness signal, while terms such as shallow, moderate, dense and very dense describe visibility. The colour and the visibility category should be read together with the location, issue time and valid period of the IMD bulletin.
This guide was checked on 4 November 2026. It does not announce a yellow warning for a particular district. The Ministry of Earth Sciences explanation of warning colours says yellow calls for watchfulness and updated information, orange for readiness to take action, and red for action. Green indicates no warning.
| IMD fog category | Visibility range in the Delhi bulletin |
|---|---|
| Shallow fog | 500 to 999 metres |
| Moderate fog | 200 to 499 metres |
| Dense fog | 50 to 199 metres |
| Very dense fog | Less than 50 metres |
Yellow fog warning meaning: what should you check?
Begin with the weather hazard attached to the colour. IMD uses colour codes for several hazards, so a yellow district on a weather map should not automatically be described as a fog alert. Read the accompanying symbol or text and the forecast date. A warning map without its legend leaves out information needed to interpret it.
Next, match the area with your actual journey or activity. A warning for one district does not describe every location in a state, and a forecast for morning hours should not be treated as an all day visibility reading. If a message has been forwarded without its issue time, return to the official bulletin before making a decision.
The colour alone also does not tell you whether a particular train or flight is delayed. Weather information describes the hazard; the operator confirms the status of a service. Travellers should check both rather than converting a general alert into an assumed cancellation. The same applies to claims of closures that are not stated in an official operational notice.
What is the difference between dense and very dense fog?
The visibility bands in the IMD Delhi daily bulletin provide a concrete distinction. Dense fog covers visibility from 50 to 199 metres. Very dense fog means visibility below 50 metres. A 50 metre observation belongs to the dense category in this legend; an observation below that boundary belongs to very dense fog.
Moderate fog is a separate band, from 200 to 499 metres, and shallow fog spans 500 to 999 metres. A report saying shallow fog occurred should therefore not be rewritten as dense fog for emphasis. Nor does a photograph, without a measured visibility observation, establish one of these numerical categories.
Delhi fog forecast checked on 4 November 2026
The Delhi bulletin issued at 20:45 IST on 4 November reports that shallow fog occurred at a few places during the morning. For 5, 6 and 7 November, its forecast describes mainly clear skies, no rain, and shallow fog or mist at a few places in the morning hours. These are the source's stated conditions, not a forecast of dense fog across Delhi.
For 8, 9 and 10 November, the same bulletin lists mainly clear skies, no rain and mist in the morning hours. This is a dated forecast, and later bulletins may revise it. Someone travelling on a later date should open the latest issue rather than relying solely on the 4 November document.
The bulletin separates past weather from the forecast and also includes district wise information. Keep those sections distinct. An observation describes what happened during a stated reporting period; a forecast describes what is expected during a future valid period. Reading a morning observation as a warning for the following night changes the meaning.
How to check official fog information before travel
Start from the IMD website and select the relevant local forecast or district warning. The department also provides an official fog warning portal. Check the latest available issue, its geographical coverage and its legend. Where an interactive display does not load, use the published bulletin rather than filling the gap with an assumption.
For a morning journey, read the conditions for the hours in which you will be outside, then check the operator's departure information separately. If the operator changes a schedule, keep that message with the booking details. A weather screenshot does not replace a train running update, an airport notice or instructions from local authorities.
Our NTES running status guide explains the rail check. For dated local context, see the earlier Uttar Pradesh fog report and an earlier Delhi weather report. Their dates matter: none should be treated as a current warning simply because winter conditions are being discussed again.
