The western end of the monsoon trough presently lies along the foothills of Himalayas and is expected to get active after the next twenty four hours and bring rain over Delhi and in northern parts of Madhya Pradesh. This spell of showers is likely to sustain for the next two to three days.
Monsoon trough is essentially intensified moisture laden monsoon winds.
Troughs are places where winds from opposing directions meet (or winds turn) and atmospheric pressure is low while the turbulence caused by such interaction (or turning) leads to rain, thundershowers and storms. Southwesterly winds are turning into northwesterly along this trough.
Northwest plains of Punjab and Haryana would also get appreciable rainfall due to the mixing of moisture from the Western Disturbance with the monsoon trough.
Thick clouds are being observed over east Uttar Pradesh, Bihar and northeastern states. A cyclonic circulation exists over east Uttar Pradesh and Bihar. This will usher in rainfall in east UP, Bihar, sub-Himalayan West Bengal, Sikkim Assam and Meghalaya.
Northern areas of West Bengal, Sikkim, Assam, Meghalaya and Bihar are expected to receive heavy rain at a few places during the next 48 hours.
Thunder showers or rain is possible at a few places over sub-Himalayan and Gangetic West Bengal, Bihar and northeastern states.
This circulation is expected to mix up with the western part of the monsoon trough during the next thirty six to forty eight hours. It would to bring rain in central parts of Uttar Pradesh in Kanpur, Lucknow and Allahabad.
The eastern extension of the monsoon trough is passing through east Uttar Pradesh, Bihar and West Bengal.
A circulation exists over north Bay of Bengal and is likely to intensify after forty eight to seventy two hours.
Mix up of the southward moving monsoon trough with the circulation over north Bay of Bengal is expected in the next thirty six to forty eight hours. This will bring rain over Orissa, coastal areas of Andhra Pradesh and south Chattishgarh.
Moisture laden southeasterly winds will then reach up to Vidarbha, north Telengana, south Madhya Pradesh in the next forty eight hours. Heavy rainfall is likely to lash these places after two to three days. Rain over these areas is likely to sustain for next three to four days.
The active offshore trough from Konkan to Goa coast is delivering rain in the coastal areas of west coast. Moderate rain is likely to continue in the coastal areas. Heavy rain at a few places over Goa Karnataka is expected in the next twenty four hours.