1. New Approaches for Nowcasting Winter
Road Weather Over a Complex Orography
Willi Schmid, meteoradar gmbh
Albert Mathis, AnyData ag
Urs Keller, MeteoSwiss

2. Decision making Snow removal / salting Traditional Modern
RWIS-stations
Weather-forecasts
RWIS-stations
Weather-forecasts
Road-forecast

3. Road forecast 0-2 hours Advection Precipitation Temperature
RWIS-station
Road-forecast

4. Our Goal To develop fully automated procedures, providing
Good probability forecasts for critical road parameters
Good threshold values for correct decisions

5. Issues of this presentation
Detection of winter precipitation with radar
Precipitation type (rain/snow/black ice) from radar/ground data
Radar image extrapolation
Cloudiness from temperature measurements
Surface temperature forecasts from extrapolated cloudiness
Risk forecasts snowfall/black ice/freezing rainwater
Road state forecasts from radar and ground data
Intervention management

6. Comparison radar – optical sensor on ground
Radar and reality
Comparison radar – optical sensor on ground
Radar-detected precipitation is confirmed on the ground in 65% of all cases.
Precipitation on the ground is seen with radar in 35% of all cases
Explanation ?

7. * * * * * * * Fraction of snow in precipitation P = 1 o o o o o o o
KSSG – method (Koistinen/Saltikoff/Schmid/Gjertsen)
P = 1 T * * T T * T * * T * * o o o o o o o

8. Melting layer

9. Validation KSSG method
Jan / Feb 2004
KSSG method
Radar / Anetz
72 stations
Switzerland
Temperature/Humidity
10 min
Optical sensor
PWD11 (Vaisala)
52 stations
Canton of Luzerne
Rain / snow direct
15 min

10. KSSG and reality 92.4 % are correct Rain predicted Snow Total observed
3311
29.8%
790
7.1%
4101 59
0.5%
6939
62.5%
6998
3370
7729
11099
100%
92.4 % are correct

11. Radar image extrapolation

12. COTREC / Raincast / Raincast+
COTREC radar image extrapolation, ETH Jürg Joss, Li Li, Susanne Mecklenburg
Raincast risk forecast rain/hail, ETH, 1999 – 2001
Raincast+ risk forecast snowfall/black ice,

13. Risk forecast precipitation.
Risk
100% 0%

14. Risk forecast snowfall/snow cover

15. Thesis Tobias Grimbacher, IACETH, 2004
Cloudiness
Thesis Tobias Grimbacher, IACETH, 2004
Temperature 2m above ground
Surface temperature

16. Cloudiness
Precipitation
Overcast
Cloudy
Clear

17. Ground temperature extrapolation
Based on extrapolated cloudiness +
Reliable method
Cheap measurements
Errors treatable
Extrapolation possible
Forecasts 1 hour -
Dense network required
Need more validation
Grimbacher et al.
To appear in Meteorol. Appl.

18. Projects 1999 – 2005 - ... COTREC / RainCast radar image extrapolation
Precipitation type rain / snowfall / freezing rain
Cloud cover freezing rainwater
Intervention management IMWS

19. IMWS = Intervention management winter service
The IMWS project ( )
IMWS = Intervention management winter service
Canton of Lucerne,
Albert Mathis
13 decision criteria
Precipitation
Clouds
Fog
Decision go/nogo
Hit rate: better than 95 % !

20. References