Hail will also appear a lot in the North in the near future

At noon on March 29, in Yen Bai city and the districts of Yen Binh, Van Yen, Van Chan. the scene of the bright sky suddenly turning black as ink continued to appear. Immediately after that, a shower accompanied by a thunderstorm appeared. This phenomenon has received attention from the online community. Many people were surprised because this phenomenon just appeared on the afternoon of March 28, surprising many people.

On April 5-6, hail may continue to occur

At 7:00 a.m. on March 29, it rained in Vinh city (Nghe An), the sky was as dark as night, vehicles had to turn on their lights to move. The sky turned dark with wind and rain, although before that, it was normally bright.

Dense hail has continuously appeared in many northern mountainous provinces in recent days.

Dr. Nguyen Ngoc Huy, an expert on climate change and natural disaster warning, said that the cause of this phenomenon is due to the large temperature difference between layers of the atmosphere. During the period from March 31 to April 4, a heat wave occurred, causing the land surface temperature to increase, favorable for water evaporation.

The phenomenon of the sky suddenly darkening and then hail occurring may repeat on April 5 or April 6 in the Northern provinces. Specifically, on April 5 or April 6, cold air will cause high-density water vapor condensation and form cloud columns 8,000-10,000 meters high, where water vapor crystallizes into crystals. stone. The ice crystals are forced by gravity to fall to the lower level, but they are pushed back by the heat from the ground surface to the colder upper level and crystallize with more water vapor until the ice is large enough to form. If it can resist the push of the heat, it falls to the ground as hail.

When observing a dark sky, it is when dense and high clouds cover the sunlight. At that time, people should take shelter in their houses and take their vehicles to a covered place to avoid breaking mirrors or lights. Hail occurs within a short period of less than 20 minutes and usually does not repeat within the same day in the same location.

Prevent damage from hail

Mr. Vu Anh Tuan, Deputy Head of Weather Forecasting Department, National Center for Hydrometeorological Forecasting, said that the northern mountainous provinces are being affected by three weather patterns . That is weak cold air that continuously strengthens in the North, the hot low pressure area in the west develops and expands and converges winds at an altitude of 5,000 m moving from west to east.

"The combination of these three factors creates a huge air disturbance in the North, especially the mountainous provinces," Mr. Tuan said, saying that this phenomenon is not unusual. Every year, hail appears at the transition from cold to hot (February to May) or vice versa from hot to cold (October to November).

According to experts, forecasting thunderstorms and hail is relatively difficult because it must identify areas of wind convergence as well as major disturbances in the air. Even if an area with major disturbance is identified, it is not certain that thunderstorms or hail will occur. Currently, the meteorological agency can only forecast 24 hours in advance and warn 30 minutes to 3 hours in advance for specific areas.

To minimize damage caused by hail, the National Steering Committee for Natural Disaster Prevention recommends that people recognize the signs. It was a dark, breast-shaped cloud coming, strong winds, and a sharp drop in air temperature . If you are walking on the road and encounter hail, people should stop and find shelter, wear a helmet to avoid rocks falling on their heads, and wait for the rocks on the road to melt before continuing to walk to avoid slipping and falling.

People need to regularly check the condition of the roof and reinforce the roof. In key places, materials that can withstand impact should be used. The roof should slope down on both sides to help reduce impact force from hail. With crops that are easily crushed, people can build trellises along the beds.

During the hot and humid period, the water vapor content in the air is high. The lower atmosphere receives a lot of heat energy and will heat up, forming a hot lower air column and cold upper air column. At this time, the convection phenomenon arises, creating cumulonimbus clouds. The air flow rising in the cloud is very strong, supporting the ice particles and growing larger, eventually becoming ice cubes with many alternating clear and opaque layers. When the ice is so large that the upward air flow can no longer support it, it will fall to the ground, causing hail.