Radar nowcasting · Operational meteorology

One-minute phased-array radar for high-impact weather nowcasting

Analysed one-minute dual-polarisation radar observations of hail, a waterspout and an airport-area squall thunderstorm.

Hong Kong Observatory · Guangdong–Hong Kong–Macao Seminar2023

Plan view and vertical Doppler-velocity cross-section from the Sha Lo Wan phased-array radar during the Cheung Chau waterspout case at 10:17 HKT on 8 June 2022.

1 minvolume scan

68elevation layers

30 mhorizontal resolution

3event studies

01 / Question

Why this problem mattered

Conventional radar volume scans can miss important stages of rapidly evolving convection. The Sha Lo Wan X-band dual-polarisation phased-array radar offered much faster updates and denser vertical sampling, creating an opportunity to examine how those observations could support operational diagnosis and nowcasting.

02 / Approach

From physical fields to usable evidence

Analysed hail over eastern Hong Kong, a waterspout near Cheung Chau and a severe squall thunderstorm near Chek Lap Kok during 2021–2022.
Combined reflectivity, Doppler velocity, hydrometeor classification and differential-reflectivity products to diagnose three-dimensional storm structure.
Compared selected signatures with observations from Hong Kong's C-band and S-band radars to understand the advantages and constraints of the X-band system.

03 / Result

Rapid updates captured storm-scale structures with direct nowcasting value.

The radar resolved hail signatures aloft, a waterspout-associated velocity couplet extending through several kilometres, and the evolving outflow and dual-polarisation structure of a severe airport-area thunderstorm. At Chek Lap Kok, the 19:04 HKT Doppler-velocity cross-section and surface winds observed one minute later documented the same rapidly changing low-level outflow environment. The one-minute volume updates made this evolution much easier to follow.

Original seminar slide showing a red box around the Cheung Chau waterspout velocity couplet and its vertical cross-section — Cheung Chau waterspout at 10:17 HKT on 8 June 2022. The red box locates the velocity couplet in plan view; the cross-section shows opposite-signed Doppler velocities extending to about 5 km, over a horizontal scale greater than 1 km, with maximum wind speeds above 16 m/s.

Three-kilometre CAPPI reflectivity with hail-producing cells circled over eastern Hong Kong — Hail case at 12:00:51 HKT on 16 September 2021. The white circle isolates the compact convective cells examined over eastern Hong Kong.

Doppler velocity, reflectivity and an A to B vertical cross-section through the Chek Lap Kok storm — Chek Lap Kok storm at 19:04:21 HKT on 18 September 2022. The 0.9° velocity field defines the A–B transect; the red ellipse in the cross-section highlights the narrow low-level velocity feature beside the storm, while the reflectivity inset shows the corresponding convective core.

Surface wind observations around Lantau and Chek Lap Kok one minute after the radar cross-section — Surface winds at 19:05 HKT, one minute after the radar panel. The observations show a sharp directional contrast between the waters north-west of Lantau and Chek Lap Kok airport, providing surface context for the radar-observed outflow.

Implications

The case studies demonstrate how rapid scanning, dual polarisation and fine spatial sampling can complement a conventional radar network. The strongest operational value is not a single new product, but a denser view of storm evolution that can support diagnosis of hazards developing on minute-scale timelines.

Limitations

This was an event-based, preliminary evaluation rather than a statistical verification study. X-band attenuation, terrain blockage, range limitations and differences between radar sites complicate direct comparison. More cases and operational verification would be needed to quantify forecast improvement.

Project material

Official HKO reprint ↗