As the monsoon withdraws from the country towards the end of September, the wind direction shifts, signaling the onset of winter. This year, due to the prevailing El Niño effect in the Pacific Ocean, the Meteorological Department has forecast slightly colder-than-average conditions. However, signs of winter are already being felt in North and Central India. People often wonder how one can predict unseasonal rain or intense cold spells during the winter season. Accurate forecasts are determined through the scientific study of atmospheric pressure, wind speed, and moisture originating from the Mediterranean region. A unique weather system is the primary cause of rainfall in the plains during winter. It originates from low atmospheric pressure systems over the Mediterranean and Caspian Seas. From there, moisture-laden winds travel rapidly from west to east, reaching northwest India. This system is responsible for unseasonal rain and hailstorms in the plains, as well as heavy snowfall in mountainous regions.
How can we get an indication of rain during winter?
To forecast changes in the weather, scientists closely monitor cloud formations and wind direction. If dense fog or clouds suddenly appear at night and atmospheric humidity rises, the night-time temperature increases slightly instead of dropping. Additionally, when winds shift from the north to the east or south-east, they bring warmth and moisture. This pattern increases the likelihood of light to moderate rainfall in the plains.
How does snowfall occur?
Conversely, when strong, icy winds blow from the snow-covered Himalayas towards the plains, there is a sudden and drastic drop in temperature. Furthermore, if the sky is completely clear and blue on a winter night, the Earth releases all the heat absorbed during the day into space without obstruction. Scientifically, this process is known as terrestrial radiation. This loss of heat at night leads to heavy snowfall, dense fog, and an intense cold wave at dawn.
Why does it feel intensely cold after winter rain?
The cycle of winter rain differs significantly from that of the summer monsoon. Under normal circumstances, sunlight causes water to evaporate, whereas in winter, moisture is brought in directly by Western Disturbances. When snowfall occurs in the plains, the humidity level in the air rises. And the temperature drops significantly. This combination of humidity and low temperature cools the atmosphere, making it feel cold even when the sun is out right after the rain stops.
