Yellow Alert, Orange Alert, Red Alert: What These IMD Weather Alerts Mean In Winter

A colour code serves as a signal for the disaster management authorities about the impact of the weather expected so as to keep them ready for necessary action related to disaster risk reduction. 

A cold day in Delhi and (inset) the colour codes used by IMD for weather warning | Photo: Getty/IMD

New Delhi: The India Meteorological Department (IMD) issued a yellow alert for Delhi for Monday, along with Uttarakhand, hinting at severe cold wave conditions. A yellow alert also signifies that the weather could change for the worse, and hence people should be vigilant.

The IMD issues district-wise and subdivision-wise warnings, and district-wise and station-wise Nowcast warnings, which describe the current state of the weather in detail and predict likely changes in the next few hours, across India. District-wise warnings for severe weather such as thunderstorm, heavy rainfall, for five consecutive days, are provided by the IMD in colour-coded form for the public to easily understand the weather conditions in a particular area.

The different colour codes signify the intensity of the weather conditions in that specific area. According to the Standard Operating Procedure - Weather Forecasting and Warning Services for 2021 provided by the IMD, "colour codes are used in weather warnings for bringing out the severity of the weather phenomena expected".

These warnings are mainly meant for administrators to keep ready and position their resources to handle situations arising out of weather-related disastrous events. 

Green Alert: This represents 'No Warning', and means 'No Action' is required.

Yellow Alert: This means 'Watch', and calls for administrators to 'Be Updated'.

Orange Alert: This represents 'Alert', and calls for administrators to 'Be Prepared'. 

Red: It's a 'Warning', and is a call to 'Take Action'.  

A colour code serves as a signal for the disaster management authority about the impact of the weather expected so as to keep them ready for necessary action related to disaster risk reduction. 

District-wise Nowcast warnings are provided graphically on the map with different colours by the IMD. A weather forecast in which the details about the current weather and forecasts upto a few hours ahead, but less than 24 hours, are given is called Nowcast.

In the national-level weather warnings in map form, red color over a state does not mean the entire state is under threat, unless otherwise explicitly mentioned, according to the IMD. 

In order to decide upon the colour to be assigned to a given weather warning situation under the 5-day forecast scheme, a particular matrix is followed, considering the probability of occurrence of the event, as well as its impact assessment. 

The colour code for impact-based warning for a district or subdivision depends upon many factors including meteorological factors, hydrological factors, geophysical factors among others. The factors may interact with each other, on the basis of which the impact and risk are determined. Therefore, the colour code will be decided by the forecaster by considering all factors.

Colour Codes For Heavy Rainfall At District Level

Rainfall is classified into six categories based on its severity. These are: 'Isolated extremely heavy rainfall', 'Scattered heavy to very heavy rainfall', 'Isolated heavy to very heavy rainfall (consecutively for three days)', 'scattered heavy rainfall/isolated heavy rainfall', 'If it is already flood situation and heavy rainfall is expected', and 'No heavy rainfall'. The colour coding used for the first two categories is Red. In case of 'Isolated heavy to very heavy rainfall (consecutively for three days)', Orange is used for Day 1 and Day 2, and Red is used for Day 3. The fourth, fifth, and sixth categories are represented by Yellow, Orange/Red, or Green respectively. 

The colour code used by National Weather Forecasting Centre (NWFC) for a particular subdivision as a whole may be yellow, but the colour code used by the Regional Weather Forecasting Centre (RWFC), or the State Weather Forecasting Centre (SWFC) for any district within that subdivision can be orange or red as per the weather situation expected and its impact, according to the IMD.