India Meteorological Department (IMD) has said strong north-easterly winds from the Bay of Bengal will trigger a fresh spell of light to moderate rainfall over Coastal Tamil Nadu for three days from Saturday. It would be isolated heavy over Tamil Nadu, Puducherry and Karaikal on Saturday and moderate for next five days along with Kerala, Mahe and Lakshadweep. 

Wet spell for North-West

Meanwhile, a fresh western disturbance is likely to affect North-West India from Friday, and the barrage of westerly to north-westerly winds from which might interact with easterly winds from the Bay to cause a wet spell over North-West and adjoining Central India from Saturday to Tuesday. Located on Tuesday morning to South-East Iran, the disturbance rolled out a thick envelop of fog over pockets of Punjab, Haryana, Delhi, East Uttar Pradesh, West Madhya Pradesh and Odisha during the 24 hours ending in the morning. It was moderate over West Uttar Pradesh and shallow over Chandigarh, Bihar, Coastal Andhra Pradesh and Tripura. 

Visibility brought to nil

This brought visibility to nil at Amritsar, Patiala, Palam, Ambala, Varanasi, Prayagraj, Guna and Paradip; to 200 metres at Safdarjung, Jhansi, and Lucknow; and 500 metres at Chandigarh, Gwalior, Bhubaneshwar, Purnea, Vijaywada, Agartala and Kailashahar. Western disturbances play a big role in amplifying winter weather over North-West, Central and East India. 

Western disturbances are low-pressure belt of winds passing frequently across Iran, Afghanistan and Pakistan before entering North-West India. They carry a ‘steam engine’ at front, spraying moisture that forms clouds, snow or rain over the hills and lightning or thundershowers over the plains. Temperature cools at their rear, giving rise to snap cold waves at times. Depending on whether the air is already cool from the passage of a preceding disturbance, an incoming one sets up dense fog conditions.

Minimum temperatures up

Minimum temperatures are currently in the range of 6-10°C thanks to clouds set up by the incoming disturbance over Punjab, Haryana, Chandigarh, Delhi and West Uttar Pradesh and 11-12°C over Rajasthan, East Uttar Pradesh, North Madhya Pradesh and parts of Chhattisgarh and Jharkhand. These are 2-3°C above normal over parts of Punjab, West Rajasthan, Uttar Pradesh, North Odisha and Madhya Pradesh; over many parts of Bihar, Jharkhand, plains of West Bengal, Gujarat and North-East India. 

An IMD outlook said dense to very dense fog conditions may persist in the early hours/morning hours for next three days over pockets of Punjab, Haryana, Chandigarh, Delhi and Uttar Pradesh as the disturbance closes and moves into Afghanistan and Pakistan. Dense to very dense fog may prevail over Rajasthan and North Madhya Pradesh on Tuesday and Wednesday. 

Fog to spread to East India

These conditions may spread to the East in line with the movement of the disturbance to isolated pockets over Odisha on Tuesday and Wednesday; over Uttarakhand for three days from Tuesday; over Jammu & Kashmir on Wednesday and Thursday; over Punjab, Haryana, Chandigarh, Delhi and Uttar Pradesh on Friday and Saturday; and towards farther East over Assam, Meghalaya, Nagaland, Manipur, Mizoram and Tripura for five days from Tuesday. 

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