Severe convective weather is "temperamental", and the "killer weapon" to subdue it: short-term nowcast

□ Science Times reporter Hu Lijuan

Recently, Beijing issued a short-term weather forecast, warning that most parts of the city will experience heavy rainfall, and parts of Miyun, Huairou, Pinggu and Shunyi will receive more than 150 mm of rainfall in 24 hours, and that people should be careful to prevent secondary disasters such as landslides, mudslides, and urban waterlogging. So, is short-term forecasting difficult?

For severe convective weather with short duration and fast changes

Short-term nowcasting includes short-term forecast and near-term forecast. Generally speaking, the weather forecast for the next 0-2 hours is called a nowcast, and the forecast for 2-12 hours is called a short-term forecast.

my country is located in the East Asian monsoon region, where cold and warm, dry and wet air frequently converge, and the convective system is active in the warm season, often producing severe convective weather such as short-term heavy rainfall and hail. These weather events are often sudden, small-scale, and fast-evolving. Therefore, it is particularly important for the meteorological department to monitor and forecast severe convective weather and prevent risks.

Cao Yunchang, chief scientist of the Meteorological Observation Center of the China Meteorological Administration, said in an interview with the Popular Science Times that compared with longer-term weather forecasts, short-term nowcasts have a shorter validity period and a shorter life cycle, only a few minutes to tens of minutes, and no longer than a dozen hours. This type of forecast is mainly carried out for small and medium-scale weather, especially severe convective weather, to prevent emergency local severe storms and other disastrous weather, and to meet the meteorological needs of various economic sectors and social public activities.

Insufficient understanding of the mechanism makes monitoring difficult and the technology difficult

The development of severe convective weather forecast in my country can be traced back to the 1950s and 1960s, and it originated from the most urgent livelihood needs - how to reduce the impact of hail on agricultural production. Since 1998, a new generation of weather radars have been built in various parts of the country, laying the observation foundation for the comprehensive implementation of short-term forecast and warning of severe convective weather. In 2004, the China Meteorological Administration issued the "Trial Measures for the Issuance of Early Warning Signals for Sudden Meteorological Disasters", which stipulated the severe convective weather warning signals. In 2005, the National Meteorological Center began to produce severe convective weather forecasts.

Traditional nowcasting technology is mainly based on the extrapolation forecasting method. Simply put, it is to predict which areas may be affected by the convective system and the weather it produces by calculating the historical movement path of the convective system.

Cao Yunchang said that nowadays, short-term nowcasting has applied new technologies such as big data. Short-term nowcasting mainly relies on mesoscale numerical models, as well as data from radars, satellites and ground monitoring networks with high temporal and spatial resolution. By combining the forecast of mesoscale numerical model data, the diagnosis and analysis of short-term observation data, and the development mechanism of severe convective weather, it can accurately give precise forecasts for specific areas, specific weather and specific short periods of time.

However, severe convective weather is characterized by its unpredictable nature and rapid development and disappearance. Therefore, short-term and nowcasting remains a problem worldwide.

In this regard, Cao Yunchang introduced three challenges. The first is the accurate monitoring and diagnostic analysis of small-scale severe convective weather; the second is the precise mesoscale numerical forecast model and rapid data assimilation technology; the third is the understanding of the formation mechanism of severe convective weather, such as hail, thunderstorms, gale, and short-term heavy rainfall.