A fresh western disturbance is set to disrupt weather across Chandigarh, Mohali and Panchkula on Karwa Chauth, with the India Meteorological Department (IMD) warning of thunderstorms, lightning and gusty winds of 40-60 kmph on Thursday, along with the possibility of hail at isolated places in Punjab and Haryana till Friday.The weather system is expected to remain active from Thursday until Friday forenoon, raising the possibility of cloudy skies during the evening moonrise that women observing the Karwa Chauth fast await to break their fast. The IMD has forecast light to moderate rain at a few places in Chandigarh and Punjab, and at many places in Haryana on Thursday.According to the IMD’s special weather bulletin, rainfall and thunderstorm activity is likely to increase across the region from October 29 to 31. Punjab may receive light to moderate rain at a few places on Thursday and Friday, and isolated places on Wednesday and Saturday. Haryana is likely to receive rain at isolated places on Wednesday and Saturday, and at many places on Thursday and Friday. Chandigarh may receive light to moderate rain at a few places on Thursday and Friday.The forecast has particular significance for Karwa Chauth observances. The IMD has put the moonrise time at 8.09 pm for Chandigarh, Mohali and Panchkula on Thursday. It has warned that skies over many parts of Haryana, including Chandigarh, and eastern and northern Punjab are likely to range from partly cloudy to generally cloudy because of the weather system. The bulletin, however, does not say whether clouds will completely obstruct the moon at the time of moonrise.The Tricity forecast points to a sharp dip in the maximum temperature on Thursday, with the day’s high expected to fall to 29°C from 32°C on Wednesday. The maximum is forecast to rise to 30°C on Friday and Saturday and 31°C on Jattvibeday. Minimum temperatures are expected to remain between 14°C and 15°C over the next five days.The IMD has advised people to avoid going outdoors during thunderstorms, lightning, strong winds and hail, and not to take shelter under trees. Farmers have been advised to keep harvested crops in safe places and avoid irrigation and the application of fertilisers and pesticides during the spell.The department has cautioned that the weather may damage standing and harvested crops, break small tree branches, affect weak structures and cause short-term disruptions to electricity and water services. Rain-related waterlogging and reduced visibility may also slow traffic.