In the early morning of April 16, thunderstorms accompanied by hail poured down on the highland commune of Bac Ha (Lao Cai), where the altitude is nearly 1,000m. Stones fell thickly, many large stones, hitting the roofs and roadbeds, creating loud noises that lasted for a long night.
Lao Dong Newspaper reporters exchanged with Dr. Truong Ba Kien - Deputy Director of the Center for Meteorology and Climate Research, Institute of Meteorology, Hydrology, Environment and Marine Science to give opinions and warnings surrounding this phenomenon.
Dear Dr. Truong Ba Kien, what is the mechanism causing ice rain and does the continuous appearance of ice rain in the recent past reflect the unusual nature of the weather?
- Ice rain forms in deep convection 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 the humid air is lifted up, it will reach saturation, water vapor condenses on the cloud condensation nuclei to create cloud droplets. When continuously brought to the negative temperature zone, the super-cold water droplets freeze on the ice nuclei and grow larger through the accretion process.
Under the influence of strong ascending currents, 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.
Regarding the phenomenon of ice rain occurring in Lao Cai with very large ice grains, as well as the ice rains in recent times, it is not an unusual phenomenon. The appearance of ice rain at this time is consistent with the meteorological laws of the transitional season.
In inter-season 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 interruption.
Therefore, it helps maintain strong ascending currents and extend the lifespan of particles in the super-cold region, thereby increasing accretion efficiency and the ability to form ice rain.
Last week, prolonged hot weather in the North, with a common temperature of about 36 - 37 degrees Celsius. At that time, heat and humidity accumulate very strongly in the atmosphere. When combined with late-season cold air, the northern mountainous area at the border between the two air masses is very likely to have hail.
Sir, cold air is continuing to move south. Do you warn of the risk of ice rain in the coming days?
- Usually, March and April are the periods with the most ice rain in the year, due to the characteristic of seasonal transition, the dispute between two different gas masses.
During the day and night of April 16, cold air has begun to impact, possibly causing thunderstorms, especially in the northern mountainous provinces - where there are very high terrain conditions and atmospheric instability, increasing the risk of hail.
However, it should be noted that ice rain is a phenomenon that can only warn of dangers and cannot be accurately predicted.
The risk of ice rain during the transitional season is mainly concentrated in April, which may last until early May, when there is still a conflict between gas masses. By the end of May, small floods often appear, marking a shift to a different weather pattern.
What is the forecast for the cold air trend in the coming time, sir, what weather pattern is dominant?
- In the coming time, especially in April and early May, there is still a possibility of weak cold air waves, taking place for a short time and not causing major temperature fluctuations, so it will be more difficult to feel.
From April, hot weather is still the dominant weather pattern, but it is still necessary to prevent the risk of thunderstorms, tornadoes and hail due to seasonal changes.
Thank you very much, Doctor!
