Thiruvananthapuram, Feb. 5
The ‘active' western disturbance may have already started affecting the western Himalayan region from Friday, according to an update by the India Meteorological Department (IMD).
This is the most productive westerly system to cross in from the northwest border so far this season.
Earlier systems had lacked the depth and magnitude to trigger the kind of heavy snow and rain over the hills expected of the incumbent.
Light to moderate rain or snow will occur at a few places over Jammu and Kashmir and Himachal Pradesh during the next 24 hours and over Uttarakhand from Saturday. Isolated rain or thundershowers have been forecast over Arunachal Pradesh during the next 24 hours.
As expected, the hills and plains have seen minimum (night) temperatures shoot up under the cover of low and medium clouds (partial cloud coverage). This phase would later give rise to showers over the plains.
Minimum temperatures were above normal by 4 to 8 deg Celsius over parts of Rajasthan and Gujarat, which provide the gateway for incoming western disturbances.
The minima were lower to the east of the country with east Uttar Pradesh, Bihar, Jharkhand, parts of Orissa and the northeast seeing the mercury dip lower by 2 to 4 deg Celsius. The lowest minimum of 4.2 deg Celsius was recorded at Sarsawa in Uttar Pradesh.
Maximum temperatures were above normal by 3 to 5 deg Celsius over Jammu and Kashmir, Punjab, Rajasthan and Gujarat till such time as the skies stayed clear ahead of the arrival of the active western disturbance. They were below normal over west Madhya Pradesh and Chhattisgarh.
A further increase in minimum and maximum temperatures by 2 to 4 deg Celsius has been indicated over northwest India during the next two days.
The active western disturbance is expected to start affecting the plains of northwest India from Monday onwards, the IMD said.
Mainly northwesterly winds prevailed over the Indo-Gangetic plains on Friday.
According to the forecast up to Wednesday, widespread rain or snow with heavy to very heavy falls could occur at a few places over Jammu and Kashmir, while it could be isolated and heavy over Himachal Pradesh. Light to moderate rainfall has been forecast for the plains of northwest India.
The forecast for the week starting Friday by the US National Centres for Environmental Prediction suggested that the western disturbance could leave some ‘dry' patches in parts of the plains. These are likely to be east Rajasthan and adjoining northwest Madhya Pradesh apart from parts of Delhi and west Uttar Pradesh.
But heavy snow and precipitation amounting to 600 per cent above normal for this time of the year has been indicated all along the Himalayan region, Jammu and Kashmir, Uttarakhand and Himachal Pradesh.
The foothills, east Uttar Pradesh and Bihar, too, are expected to get precipitation amounting to between 400 to 600 per cent of the normal during the week under reference.
The confluence of northwesterly and east to southeasterly winds is expected to trigger rains over east and east-central India (up to 200 to 300 per cent above the normal for this time of the year).
The European Centre for Medium-Range Weather Forecasts has indicated that a follow-up western disturbance of moderate intensity could push into the northwest towards the latter part of next week.