Cell Tracking and Warning Indicators derived from Operational Radar Products

Online-tracking of convective cells in operational radar networks can be based on standard radar products. Then restrictions from the radar resolution in time and space have to be accepted as well as non-ideal conditions and the whole spectrum of convective cells.

The uniform products of the DWD Radar Network are reflectivity images from 16 radar stations. They each cover 400x400x12km³ volumes in 15 min steps and 200x200km² planes in 5 min time steps. For each radar station cell tracking is separately applied to the downdraft base reflectivity of the cell core (>46 dBZ, every 5min) and to the cell tower echo constellation (every 15min). The cell tracking method CONRAD (CONvection in RADar) combines the cell track, cell stage and cell identification and estimates a developing warning state, such as hail, flood and possible gusts. A simple position (+30 min) and echo trend forecast completes the general cell analysis.

CONRAD was tested online during the convective season 2000 at Hohenpeissenberg and other network radar stations during different conditions. Published damage reports or rescue actions were checked for corresponding cell warnings issued by CONRAD.

Fully developed cells with a 46dBZ downdraft rain are identified and characterised by a list of 40 parameters, containing a VIL-dependent cell stage , hail indicator, cell core centre and lifetime. For the multi-user visualisation simple symbols and colours were chosen, giving the cell core position and warning status in a sufficient resolution.

In the offline version of CONRAD the cell tracks and warning sequences of several hours can be shown, in the online version the latest cells and their 30min or 60 min history (track and warnings) as well as their forecast are shown.

For mostly night-time ANAPROP situations at non-Doppler radars a simple gradient-algorithm is often capable to identify stationary artificial cell tops with their high false alarm potential of flood warning.

New developing cells and their beginning lightning activity are identified as secondary cell towers in the reflectivity volume but are not tracked until reaching 46 dBZ at ground. Squall line structures were made obvious by the line shape of incorporated cells and their combining 30 dBZ reflectivity which completes the latest stage in the online product .

After the 2000 season some parameters and algorithms of CONRAD are still in modification and some cell statistics are in progress.

The 15 min cell tracking occasionally led to false cell tracks by false cell combinations compared to the 5min tracks. Additionally, equivalent cell stages and warnings were differently estimated by two radars which emphasises the necessity of well-calibrated network radars in Nowcasting.