1. Daniela Rezacova, Zbynek Sokol IAP ASCR, Prague, Czech Republic
THE USE OF RADAR DATA IN THE VERIFICATION OF A HIGH RESOLUTION QUANTITATIVE FORECAST OF CONVECTIVE PRECIPITATION
Daniela Rezacova, Zbynek Sokol
IAP ASCR, Prague, Czech Republic

2. MOTIVATION
convective storms  local heavy rainfalls  rapid hydro response  flash floods
QPF/warning  difficult
operational NWP models  x ~ the order of 1km ~ radar resolution
assessment of the QPF accuracy and/or QPF uncertainty
model improvement
interpretation of the forecast

3. Outline LM COSMO LLM : 231x175 g.p., 11km 00UTC+24h, init.con. ECMWF
SLM : 251x191 g.p., 2.8 km 06UTC+18h, init.con. LLM
A cluster of 9 forecasts – shifting the LLM init. fields
CZRAD-CHMI, 2 radars
Gauge adjustment
A verification of QPF{SLM}
local flash flood storm
SLM: 703x535 km
Verification domain
165x95 g.p. (462x266 km)

4. Convective event 150702 15/7/2002 multicellular convection
15-17UTC: convective storm in nearly steady position,
 daily max. ground rainfall 171 mm
local flash flood, local damage 
14 – 19 UTC

5. Rainfall UTC
R+G 
LLM, SLM 

6. Modification of LLM initial conditions
AT500 at 12UTC
NS shifts – upper fig.
WE shifts – lower fig.
AT500 + AT850 in the extend.abstract.
Shift of LLM initial conditions
4 cardial directions
0.5°, 1.0° ( 50, 100 km)
9 LLM + SLM forecasts

7. LLM  SLM rainfall Comparison of LLM and SLM produced QPF
Basic structures similar
SLM - finer area structure of convective rainfall
linear shift implies a nonlinear QPF change
LLM  SLM rainfall
Comparison of LLM and SLM produced QPF
Shifts in NS and WE directions
Accumulated Precipitation 00UTC-18UTC
Domain with AP>15 mm

8. QPF verification by R+G
R+G prec.  SLM g.p.  forecast prec.
Contingency table (Rez. et al. 2004, 2005)
Area related RMSE (N, [x.y])
Precipitation over a square of N*N g.p. centered in each g.p.
f.A
f.B
„True“
(A) =  (B) =  (True)
preference to f.A over f.B
RMSE (N,[x,y]) = RMSE (F, T)
F  {fi},, f1  f2 .. fN*N , T  {ti},, t1  t2 .. tN*N

9. RMSE - modified inputs area element: 11x11 g.p. 30.8x30.8 km
(+) R+G > F
(-) R+G < F
forecast underestimation in the storm position
overestimation east from storm position
the “best” forecast produced after 0.5S shift

10. RMSE - modified inputs

11. mean RMSE relative to mean R+G
horizontal axis: length of the square side [g.p.] / [km]
mean prec. [mm]
R+G : 1.98
LLM : 2.68
<2.18, 4.14>
SLM : 2.70
<2.10, 3.42>
LLM
SLM

12. CONCLUSION-OUTLOOK Preference of the QPF{SLM} to the QPF{LLM}
Proposed verification technique (i) is simple, (ii) agrees with the verification “by eye”, and (iii) takes into account the area extent (scale).
The creation of QPF cluster (“ensemble”) by shifting the init.cond. proved to be a useful technique to study the QPF uncertainty.
Outlook: probabilistic forecast (using 2,3)
Acknowledgement: DWD (LM COSMO), CHMI (radar data), ECMWF (analyses), COST717

13. Thank you

14. 130702: mean 6.12, std 7.69
LLM; mean
LLM; std
SLM; std
SLM; mean

15. mean RMSE relative to std R+G
LLM
std [mm]
R+G : 5.19
LLM : 6.75
<4.93, 10.05>
SLM : 5.70
<4.98, 6.63>
SLM