Explainer: Hail, showers not uncommon in summers, expect wet spell for another 7 days
Over the past couple of days some places in northwest India, including the sweltering plains, experienced hail storms, with the weather department forecasting the possibility of more such events over the next seven days.
Thunderstorms accompanied with squalls or gusty winds with speeds of 40-70 kmph prevailed at some places in Punjab, Haryana, Himachal Pradesh and Chandigarh during the past 24 hours, with rain keeping temperatures below normal by up to 5°C. Moderate rain was also experienced in some parts on Monday morning.
Despite high temperatures, hailstorms are not uncommon in summers. Hail stones are basically frozen raindrops and are of various sizes ranging from a few millimetres across to several centimetres.
Hailstorm activity over India is seasonal and mainly occurs from March to June, according to available data, when the region experiences pre-monsoon showers resulting from western disturbances. Their intensity can range from light showers to heavy and persistent thunderstorms.
Studies conducted by the India Meteorological Department (IMD) show that in north India, Himachal Pradesh and Punjab experience maximum hailstorms compared to other states in the region. Data shows that since 1982, at least one hailstorm has been experience in the states of Punjab, Haryana and Himachal Pradesh from February to May, with the monthly number peaking at 13 in Himachal Pradesh and eight in Punjab.
Hail stones are formed when raindrops are carried upward by thunderstorm updrafts into extremely cold areas of the atmosphere, where they freeze. They can grow in size by colliding with liquid water drops that freeze onto their surface.
The formation of hail requires a strong upward motion of air within the prevailing thunderstorm and lowered heights of the freezing level. Hail generally occurs during a thunderstorm and is formed by type of clouds called cumulonimbus, which can rise up to heights of 52,000 feet.
According to experts, if the temperature on ground is 40°C, the atmospheric temperature at an altitude of 25,000 feet would be around -10°C and at 50,000 feet it would be around minus 55°C.
Since they are solid and travel at high velocity, hail stones can cause injuries or even death, and also damage property and effect standing crops and fruit trees. There have been numerous instances in the past when crops have been damaged by hail.
In India, the worst hail storm to be recorded as Moradabad in Uttar Pradesh in April 1888 that killed 246 people and 1,600 livestock with hailstones being as large as “cricket balls”.
The record for the heaviest hail stone is 1.02 kg that fell in Gopalganj District of Bangladesh in April 1986, while the largest diameter officially measured is 20 cm at South Dakota in July 2010.
A bulletin issued by IMD on May 5 stated that a western disturbance is prevailing over central Pakistan adjoining Punjab and north-west Rajasthan in lower to upper tropospheric levels. An upper air cyclonic circulation lies over north-east Rajasthan and its neighbourhood and another lies over south Pakistan and adjoining south-west Rajasthan in lower tropospheric levels. These weather systems are responsible for the ongoing wet spell.
Scattered to fairly widespread light to moderate rainfall with thunderstorm, lightning and gusty winds are likely over Punjab, Haryana Chandigarh, Delhi, Himachal Pradesh Jammu and Kashmir and Ladakh till May 11, along with the possibility of hailstorm at a few places.
The weather department does not expect any significant change in the maximum temperature over northwest India during the next four days, following which a rise by 2-3°C is likely.
