Union Territory Chandigarh, common capital of the two states, was lashed by heavy showers since morning, causing a sharp fall in mercury.
The showers are likely to ease power situation in Chandigarh and other parts of the region, where power cuts had added to the woes of the people braving hot weather earlier.
"Pre-monsoon" showers lashed almost entire Punjab including Ludhiana, Bathinda, Jalandhar, Pathankot, Amritsar, Hoshiarpur, Mohali and Ropar, causing a fall in maximum temperatures, Director of the Chandigarh's MeT Department Surinder Paul said.
He said that southwest monsoon can be expected to hit the two states and Chandigarh over a week in advance.
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While the normal date of arrival of monsoon in the region is between June 29 to July 5, this year it is expected to arrive around June 20, Paul told PTI.
Agriculturists say that rain is highly beneficial for paddy growers.
Continued rain will also help replenish depleting underground water table.