Since May 2001 ZAMG has been running a hail warning procedure. To manage these special warnings we set up a project with the goal to reach the best reliable warning for our clients.
The target of the project:
Hail is in principle possible in each thunderstorm.
How can we filter those thunderstorms which are capable of producing hail?
The maximum range of the forecast time for hail according to the synoptic scale lasts only 1 hour.
The object is to reach a low false alarm rate.
The available tools:
SYNOPS, METARS, automated observations of 126 stations over the territory of Austria
Radar image (3D-version)
Satellite image (rapid scan, e.g. 10 minutes intervals)
Convection detecting system
Cloud motion vectors (CMVs)
Pointcasts (combination of CMVs and observations, extrapolation for the next 2 hours)
These tools are covered in the operational graphical system at the central and regional forecasting departments.
The monitoring mode:
Can we predict all hail situations? The answer is NO. Local convective systems are not predictable in time. We restricted the monitoring of hail warnings to fronts, troughs and to mesoscale convective systems. With a combination of the automatic convective detecting system and automated CMVs the forecaster gets a signal of possible hail situations taking into account the information of the lightning and radar systems.
The distribution procedure:
The identified hail phenomena and its warning for the next 15 to 60 minutes have to be distributed in time to the clients. Over the territory of Austria 500 clients are a possible number. The warning must reach them in time. With a special developed graphical mode the forecaster can determine the area relevant to the hail warning. Inside this area all clients are reached automatically by SMS, e-mail or fax. A provider was found to manage the distribution of the hail warning within the next 3-5 minutes. Thus the hail warning is in line with the predictability of hail.
The above mentioned tools, the monitoring mode and the distribution
procedure are optimized on a workstation. The distribution procedure includes
the hail warning as text information.
After the first period we have got an additional contract for the year 2002. We are in favour of our clients' information that our hail warnings had been successful.
Proceedings, EUMETSAT, Bologna, 2000 (convective detecting systems)
Proceedings, EGOWS, Zurich, 2001 (Nowcasting modules)
Dr. Herbert Gmoser
Division Head Weather Forecasting
Hohe Warte 38
A- 1190 Vienna, Austria
Dr. Michael Staudinger
Head of the Regional Office for Salzburg and Upper Austria
A-5020 Salzburg, Austria