India Meteorological Department (IMD) has warned ground frost may develop over parts of Punjab, Haryana and Rajasthan for three days until Wednesday. Strong surface winds of up to 15-20 kmph in speed on Monday over parts of the plains of North-West India could, however, blow away prevailing dense fog. Ground frost is a result of sustained lowering of minimum (night) temperatures worsened by thick fog. 

The IMD has forecast further fall in minimum (night) temperatures by about 2℃ over North-West and Central India till Tuesday 17 and gradual rise by 3-5℃ from Wednesday to Saturday. The chill will sustain also over East India before rising by 2-3℃ from Wednesday to Saturday. No significant change is expected over Gujarat until Tuesday before start night temperatures start rising.

Warmer nights ahead

Dense fog may still unfold over isolated pockets during night and morning hours over Punjab, Haryana, Chandigarh, North Rajasthan, North Uttar Pradesh, West Bengal and Sikkim on Monday and Tuesday and over Bihar, Assam, Meghalaya and Tripura during next five days on the immediate trail of an existing western disturbance with moisture and cloud moving away.

The pulsating winter weather is attributed to arrival of warm western disturbances with moisture upfront that gets dropped as snow/rainfall in the hills and thundershowers in the plains by westerlies or south-easterlies. The eastward moving western disturbances leave behind a vacuum that gets gradually filled by cold north-westerly winds. This brings the chill to the plains.

Cold good for Rabi crop

So temperatures take a dip after the western disturbance yields space to colder westerly to north-westerly winds from across the international border. Low temperatures are particularly good for the Rabi wheat crop, but fog that persists for a week to 10 days could prevent radiative heating of the plant. This can make it vulnerable to pest attack and diseases. Farmers need to be wary of these conditions, more so if the low temperatures lead to ground frost.

As forecast already, the current chill over the hills may end with the arrival of a fresh western disturbance from Tuesday night. The warm disturbance will also bring clouds along, triggering light to moderate isolated to scattered rainfall or snowfall over Jammu, Kashmir, Ladakh, Gilgit, Baltistan, Muzaffarabad, Himachal Pradesh and Uttarakhand until Friday. 

‘Active’ disturbance on way

Cold wave to severe cold wave conditions may persist over Rajasthan, Punjab, Haryana, Chandigarh and Delhi till Tuesday and in isolated pockets on Wednesday. Similar conditions are forecast over Himachal Pradesh until Wednesday; West Madhya Pradesh on Monday and Tuesday; East Madhya Pradesh on Tuesday; and Punjab, Haryana, Chandigarh, Delhi and Rajasthan on Thursday. 

But what will really set up winter weather in a fashion not seen thus far during this season is arrival of an ‘active’ or an intense western disturbance, the first of the season, from Friday night. An active disturbance can venture deeper to the South (down even to Peninsular India at times) and alter prevailing even over the southern parts of the country. It also throws up an offspring cyclonic circulation to amplify weather.

Showers for South Peninsula 

The IMD has said that the active disturbance will cause scattered to fairly widespread light to moderate rainfall or snowfall over the hills of North-West India (Western Himalayan Region) and isolated light rainfall or snowfall over Arunachal Pradesh and isolated light rainfall over the plains of North-West India. 

The US National Centres for Environmental Prediction hinted it may impact the South Peninsula by interacting with easterlies from the Bay of Bengal. The disturbance may dip down from over Uttar Pradesh and cut through Jharkhand, Chhattisgarh, Vidarbha and Andhra Pradesh bringing rain or thundershowers before spreading out over Tamil Nadu, Karnataka and Kerala. 

Unfriendly for R-Day parade?

This is expected to pan out from during the week starting January 24 and ending February 1. The IMD is not that optimistic, but indicates in numerical model predictions that rain or thundershowers are likely over Tami Nadu from Republic Day (January 26). There are indications that the active western disturbance may not ensure friendly weather for the Republic Day parade in New Delhi.