According to the National Center for Hydro-Meteorological Forecasting, currently, the cold air mass from the north compressing a low pressure trough with axis at about 24 - 26 degrees north latitude gradually moves southward.
It is forecast that due to the influence of cold air compressing low pressure troughs combined with wind convergence from level 1500m to 5000m, from the evening of April 22 to April 23 in the Northern region there will be rain, moderate rain and scattered thunderstorms with rainfall from 20 - 40mm/24h, locally heavy to very heavy rain over 100mm/24h.
From the evening of April 23rd to April 25th, in the North Central and Central Central regions, there will be scattered showers and thunderstorms with rainfall of 15 - 30mm/24h, locally heavy to very heavy rain over 100mm/24h.
The meteorological agency warns that thunderstorms are likely to occur with tornadoes, lightning, hail and strong gusts of wind.
Rainstorms accompanied by tornadoes, lightning, hail and strong gusts of wind can affect agricultural production, causing trees to fall, damage to houses, traffic works, and infrastructure. Localized heavy rains are likely to cause flash floods on small rivers and streams, landslides on slopes, and flooding in low-lying areas.
Warning level of natural disaster risk due to tornadoes, lightning, and hail is level 1.
Previously, during the rains from March to now, rock showers were recorded in some northern and western mountainous provinces of Thanh Hoa and Nghe An.
According to Dr. Truong Ba Kien - Deputy Director of the Center for Meteorology and Climate Research, Institute of Meteorology, Hydrology, Environment and Marine Science, ice rain forms in deep convective clouds when there is a strong ascending current, a humid and highly unstable environment. In the atmosphere, the average temperature decreases by about 6.5°C/km according to altitude, so when humid air is lifted up, it will reach saturation, water vapor condenses on cloud condensation nuclei to create cloud droplets. When continuously brought to a negative temperature zone, super-cold water droplets freeze on the ice core and grow larger through the accretion process.
Under the impact of a strong upward current, ice particles undergo many upward and downward cycles, accumulating concentric ice layers; when the mass exceeds the lifting force, they fall to the ground in the form of ice rain" - Mr. Kien analyzed the nature of the ice rain phenomenon.
Dr. Truong Ba Kien added that in interseas conditions, especially when late-season cold air intensifies interaction with low-lying hot and humid air masses, the two air masses have different natures, increasing atmospheric instability, convergence and vertical wind breaks.
Therefore, it helps maintain a strong upward flow and extend the lifespan of particles in the super-cold region, thereby increasing accretion efficiency and the ability to form ice rain" - Dr. Kien assessed.
According to this meteorologist researcher, usually March and April are the periods with the most hailfall in the year, due to the characteristic of seasonal transition, the dispute between two different gas masses.
In late-season cold air waves, thunderstorms can occur, especially in northern mountainous provinces - where there are very high terrain conditions and atmospheric instability, increasing the risk of hail.
However, it should be noted that hail is a phenomenon that can only warn of dangers, cannot be accurately predicted. Therefore, people need to be careful and proactively ensure safety when there is a warning of thunderstorms during the transitional season" - Mr. Kien advised.
