Biting cold, ground frost and fog have combined to set up harsh winter conditions over large parts of northwest India.
The lowest minimum temperature in the plains recorded during the 24 hours ending on Friday morning was 1.1 deg Celsius at Adampur in Punjab.
Very dense fog brought visibility to 50 m or less at Gorakhpur, Patna, Bhagalpur, Purnea, Kalimpong, Baghdogra, Jalpaiguri, Cooch Behar and Haflong in the morning.
Frost forms when the night is cloud-free, when heat can escape from the earth quicker without being blocked by the clouds.
This allows temperatures to drop to new lows. As the moisture in the air freezes, the ground will be covered with frost.
Frost conditions can impact standing crops given that even when the air temperature reaches zero degree Celsius, the crop itself can be four or five degrees cooler.
GROUND FROST This is because plants loose heat faster than the surrounding air temperatures.
On Friday, ground frost (minimum temperature below 4 deg Celsius) was reported from Punjab, Haryana and north Rajasthan.
Dense fog (visibility below 200 m) hung over east Uttar Pradesh; Bihar; sub-Himalayan West Bengal; Assam; Mizoram; and Tripura.
Moderate to dense fog (visibility below 500 m) was reported from Punjab, Haryana, Delhi, north Rajasthan, west Uttar Pradesh and northwest Madhya Pradesh.
The Met Department has forecast ground frost at isolated places over Punjab, Haryana and north Rajasthan.
Dense fog will be triggered at a few places over east Uttar Pradesh; Bihar; sub-Himalayan West Bengal; Assam; Mizoram; and Tripura.
FRESH WESTERLY Moderate to dense fog will spread over Punjab, Haryana, Delhi, north Rajasthan, west Uttar Pradesh and northwest Madhya Pradesh.
Meanwhile, the weather-setting western disturbance over Jammu and Kashmir will move away to east-northeast on Saturday.
This is expected to bring the mercury even lower since Arctic cold air will drift in from northwest in the absence of predominantly westerly winds packing a western disturbance.
Biting cold conditions may last until the arrival of a fresh western disturbance over the western Himalayan region and adjoining plains of northwest India by Monday.
It will trigger moderate snowfall over the western Himalayan region and light rainfall at a few places over adjoining plains of northwest India.