Passing of ‘active’ westerly may kick up fog in its wake

Residual moisture being left behind a prevailing ‘active’ western disturbance could settle down as fog on getting cooled by the northwesterly winds blowing in over the plains of northwest, central and adjoining east India mainly during the morning hours for at least three days from tomorrow (Friday).

An India Meteorological Department (IMD) update on Thursday morning said that the western disturbance is moving eastwards across western Himalayan region, allowing cooler northwesterlies to fill the plains.

It remains to be seen what the incremental moisture being brought to bear by a feeble western disturbance, expected to hit the western Himalayan region from Saturday onwards, does to the overall situation.

Normally, rising motion of air and convection associated with the front-end of the western disturbance should warm up the atmosphere and lead to snow of precipitation.

But the IMD doesn’t see this happening given the feeble nature of the incoming westerly system. It, in fact, sees minimum temperatures falling by 2 to 4 deg Celsius over northwest and adjoining central India during next three days.

This would mean that the influence of the westerly system would be confined just to the hills and clearer (cloudless) skies emerging over the plains of northwest and adjoining central India. This also explains the expected drop in night temperatures.

In an updated and extended forecast outlook valid until Tuesday next (February 22), the IMD has said that scattered rain or thundershowers are likely to occur over Orissa, Chhattisgarh, Vidarbha, Andhra Pradesh and Tamil Nadu.

In this manner, it has hinted at an expanded rain cover than was stated in its previous night bulletin along the east coast and immediate interior. This is in agreement with the forecast outlook maintained by leading global models.

A weather warning issued by IMD said that isolated heavy to very heavy rainfall would occur over Arunachal Pradesh and Assam until Friday. Isolated thunder squalls or hailstorms may also break out over these regions during the same period.

During the day on Thursday, fairly widespread rain or snow was reported from Jammu and Kashmir and Himachal Pradesh and scattered over Uttarakhand.

Fairly widespread rainfall has also occurred over Uttar Pradesh, sub-Himalayan West Bengal and Sikkim; scattered over Bihar, Arunachal Pradesh and Assam; and isolated over Punjab, Haryana, Delhi, Rajasthan and north Madhya Pradesh.

Maximum temperatures are below normal by 2 to 6 deg Celsius over most parts of northwest and adjoining central India; by 2 to 4 deg Celsius over west and adjoining central and south peninsular India; and over parts of east and northeast India.

Satellite cloud imagery on early Thursday morning showed convective clouds over eastern parts of western Himalayan region.

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