1. Warm front in radar images
Elena Saltikoff
Finnish Meteorological Institute

2. A warm front in radar images
Reflectivity seen in CAPPI, TOPS, MAX
Geometrical properties seen in PPI
Wind seen in PPI and as wind profiles
”Easy” case: most of the measured precipitation is snow
Melting is usual for many of you, but radarwise a challenge (more about it later)
Ikaalinen radar
Analysis 14 Jan UTC

3. Surface pressure, Temperature advection 850 hPa

4. 700 hPa humidity

5. IR Meteosat 6 UTC

7. 04:00
CAPPI 500 m
composite
(=”mosaic”)
500 m

8. 05:00

9. 06:00

10. 07:00

11. 08:00

12. Cappi TOPS

13. Cross section reveals the typical warm front shield

14. Cross section and TOPS 30 min later

15. And an hour after previous slide

16. Cappi MAX

17. Why does reflectivity grow downwards and (here) west?
Warmer air, bigger flakes
Photos snowflakes.com

18. PPI Images elevation 7 degrees

19. You should remember
That radar measurements are made on conical surfaces, so edges are higher than centre

20. First: concentrate in geometry
Why a hole ?
Why not symmetrical but an ellipse ?

21. 30 minutes later

22. Cold colours towards - reds away
Shear.
Low levels: southwest
High levels:
West (and stronger)
Warm advection

23. Enough of yin and yang ? These images are great for tornado hunting.
For simple cases of uniform wind field, there are more sophisticated tools.

24. Time series of wind barbs + reflectivity
Wind turning clockwise and growing with height: warm advection
Reflectivity growing: warmer air, larger flakes

25. Single wind profile: Speed, direction, reflectivity as averages in a 15-km cylinder

26. Wind profile 5:47 UTC (15 min after previous one)
Low level wind maximum !
Why ?

27. Wind profile still 15 minutes later

28. One hour after the previous one

29. Cold conveyor belt is visible, because it’s inside the precipitation

30. Warm front summary
Warm front is a 3-d structure: think about the shield cloud
Reflectivity depends on size and number of particles; in snowfall, it is strongly depending on temperature
The radar measures snow in all warm fronts (but sometimes it melts before falling to ground)
Details of warm front windfield, such as conveyor belts, can sometimes be seen with Doppler radar