Hail occurs due to instability in the atmosphere when cold and warm air currents meet. Therefore, during transitional months between cold and hot seasons, such as May and June, hail is more likely to form.
On the afternoon of June 14, many areas in Ho Chi Minh City experienced heavy rain, with several districts reporting hail with diameters ranging from 1 to 2 cm. On social media that afternoon, numerous news fan pages quickly shared images of the hailstorm that had just occurred, surprising many.
According to some residents, some hailstones were nearly 2 cm in diameter. (Photo: Duy Hieu, Ky Duyen).
Explaining the hail phenomenon that caused a stir on June 14, Mr. Le Dinh Quyet, Head of the Forecasting Department at the Southern Hydro-Meteorological Center, noted that the formation of hail under the weather conditions in Ho Chi Minh City on June 14 is not unusual.
“Hail is rare but does occur 1-2 times a year,” Mr. Quyet told Tri Thuc – Znews. The last recorded hail in Ho Chi Minh City was in June 2022, occurring in suburban districts such as Tan Phu and Tan Binh.
Seasonal Transition Increases Hail Chances
In fact, hail is a climatic phenomenon that occurs during the summer. This phenomenon involves precipitation falling to the ground in the form of ice pellets or chunks of ice of varying shapes and sizes, ranging from 5 mm to several centimeters. Hail typically falls along with rain showers and lasts only a few minutes, usually between 5-10 minutes, or at most 20-30 minutes.
The conditions for formation include high temperatures and humidity, with very strong convection usually accompanied by convective clouds (cumulus clouds). The rain is created during strong thunderstorms in high atmospheric layers where temperatures remain below freezing.
Transitional periods (April, May, June) are ideal for the formation of this phenomenon. During these months, the weather is hot and humid, with high moisture content in the air. Lower atmospheric layers receiving significant thermal energy warm up, creating a column of warm air below and cold air above. At this time, convection occurs, leading to the formation of cumulonimbus clouds.
At around 2:30 PM on June 14, many places in Ho Chi Minh City experienced heavy rainfall accompanied by thunder and lightning across most districts. (Photo: Duy Hieu).
Within the cumulonimbus cloud, there are many ice particles and supercooled water – liquid water that remains in a liquid state below its freezing point without solidifying due to a lack of condensation nuclei. Ice typically forms near the top of the cloud, where temperatures can drop to -60 degrees Celsius. Supercooled water tends to be closer to the lower half of the cloud, where temperatures are nearly freezing.
When thunderstorms occur, air moves violently up and down within the cumulonimbus cloud – referred to as updrafts and downdrafts.
When clouds close to the ground are lifted by updrafts, a large mass of supercooled droplets is pushed to the upper layer of the cloud. They freeze with existing ice particles in the upper layer, increasing the volume of the ice particles.
As they fall to lower cloud layers, the outer surface of the ice is coated with an additional layer of water, while being influenced by fluctuating downdrafts. The longer the ice particles are subjected to airflow, the more layers of water accumulate, further increasing the ice’s volume.
Eventually, it becomes a multilayered ice pellet interspersed with clear and opaque layers. When the ice pellet becomes heavy enough and cannot be carried away by winds or air currents, it will fall to the ground, causing hail.
Why is there no hail in winter?
Small hailstones often melt before reaching the ground, but larger ones can impact the ground and cause significant damage. Hail is most common in mid-latitudes at the beginning of summer.
Here, the lower atmosphere receives much thermal energy, leading to high temperatures, forming unstable columns of warm air below and cold air above. This is conducive to the development of convection and cumulonimbus clouds capable of producing hail.
Meanwhile, high atmospheric layers remain cold enough to support the formation and growth of large ice particles within the clouds. This is why hail can still occur in summer; although the ground-level air can be warm, it remains cold in the higher sky.
In contrast, during winter, sunlight strikes the ground at an angle, resulting in minimal heat absorption, which does not lead to strong convection. Moreover, the air tends to be dry, making it challenging to form large cumulonimbus clouds. Even if cumulonimbus clouds develop, if the updraft is not strong enough, the process of ice particle formation cannot occur. Therefore, no hail occurs in the cold season.
Many people picked up large hailstones, measuring 1-2 cm in diameter. (Photo: NVCC).
According to initial reports, during the hailstorm on June 14, hail was concentrated in District 1 and District 4, with sizes comparable to chopsticks. If the size is larger, the hail can puncture roofs, damage crops, or break windows in homes and vehicles. Mr. Quyet also noted that large hailstones falling on people can cause serious injuries.
