1. Forecasting convective initiation over Alpine terrain by means of automatic nowcasting and a high-resolution NWP model Georg Pistotnik, Thomas Haiden, Christoph Wittmann

2. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Overview Contents: 1.What is INCA, ALADIN, AROME? 2.Previous work on convective initiation (INCA / ALADIN framework) 3.Future work on convective initiation (INCA / AROME framework) – a test case 4.Conclusions and expectations

3. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge What is … INCA? high resolution analyses and (short range) forecasts (Δx = 1 km, Δt = 15min or 60 min) station measurements radar and satellite data high resolution topographic data INCA NWP model data Integrated Nowcasting through Comprehensive Analysis (INCA): http://www.zamg.ac.at/fix/INCA_system.pdf

4. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge What is … ALADIN, AROME? Limited area NWP models ALADIN and AROME: ALADINAROME update frequency:6 hours24 hours domain:Central EuropeAustria (plus near surroundings) forecast range:72 hours30 hours horizontal resolution:9.6 km2.5 km vertical resolution:60 levels treatment of convection:parameterizationexplicit simulation status:operationaltestbed use in INCA:background fieldsno

5. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Previous work INCA precipitation (2D): Analysis generated by optimized combination of station measurements and radar data Pure nowcast (extrapolation of analysis) from t 0 to t 0 +2h NWP forecast (optimized combination of ALADIN and ECMWF) beyond t 0 +6h Linear transition in-between

6. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Previous work (2) INCA temperature and humidity analysis (3D): ALADIN forecast interpolated onto INCA grid 3D correction by observations Physical assumptions to allow boundary layer effects =>Input for analysis of convective indices (CAPE, CIN, …) INCA wind analysis (3D): ALADIN forecast interpolated onto INCA grid 3D correction by observations Relaxation algorithm to ensure mass-consistency =>Input for analysis of moisture flux convergence Replace conventional nowcasting by „convective nowcasting“!

7. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge For each `convective‘ gridpoint (i.e., with CAPE > 0 J/kg):  Initiation?  Intensification?  Weakening? Previous work (3) Predicted if: CAPE > CAPE start (100 J/kg) MOCON > MOCON start (2*10 -7 /s) VIS > VIS start (0.5) | CIN | < | CIN start |(200 J/kg) ΔTtrig > ΔTtrig start (-2 K) Predicted if: CAPE > CAPE int (50 J/kg) MOCON > MOCON int (2*10 -7 /s) RR > RR int (0.2 mm/h) | CIN | < | CIN int |(200 J/kg) ΔTtrig > ΔTtrig int (-2 K) Predicted if: CAPE < CAPE weak (50 J/kg) MOCON < MOCON weak (0 /s) RR > RR weak (0.0 mm/h) | CIN | > | CIN weak |(200 J/kg) ΔTtrig < ΔTtrig weak (-4 K) RR max = RR max (CAPE, q); RR (t, RR max ) assumed to show Gaussian variation in time

8. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Precipitation analysis t = t 0 [mm/15min] Previous work (4)

9. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Initiation! Precipitation analysis t = t 0 +60min [mm/15min] Previous work (5)

10. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Initiation area CAPE analysis t = t 0 [J/kg] Previous work (6)

11. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Initiation area MOCON analysis [10 -9 /s] Previous work (6)

12. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Initiation area Previous work (7) VIS signal analysis [ ]

13. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Initiation area Previous work (8) convective nowcast of precipitation [mm/h]

14. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Previous work -> future work Verification of convective nowcast: Minor improvement in Alpine catchments Essentially neutral results in non-Alpine catchments No operational implementation yet (due to risk of false alarms) But: encouragement to resume research again =>Conclusion: knowledge of near-surface wind field is limiting factor =>Question: Can we gain any profit by using the new high-resolution AROME model?

15. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Future work – a test case (1) July 09 th, 2009 – INCA analyses 07-19 UTC

16. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Future work – a test case (2) July 09 th, 2009 – AROME forecasts 07-19 UTC –––

17. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Future work – a test case (3) ––– July 09th 2009, 11 UTC: AROME forecast (left); INCA analysis (below) primary convection

18. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Future work – a test case (4) ––– July 09th 2009, 14 UTC: AROME forecast (left); INCA analysis (below) transition from primary to secondary convection

19. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Future work – a test case (5) ––– July 09th 2009, 17 UTC: AROME forecast (left); INCA analysis (below) secondary convection

20. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Conclusions and expectations (Subjective) percipience of AROME: 1.Primary convection: Convective initiation too early and too widespread; Good skill in predicting wind field 2.Secondary convection: Usually over-estimation of convective precipitation; Wind field gets increasingly disturbed by exaggerated „model gust fronts“ =>Pre-convective wind field may prove helpful in automatized detection of convection-prone areas

21. 2009-10-27 CSIP & COPS Meeting 2009, Cambridge Conclusions and expectations (2) Goals: To improve nowcasting by adding ability to simulate initiation and life cycle of convective cells Comparison between advanced nowcasting methods and high- resolution NWP model Validation of strengths and weaknesses of a high-resolution NWP model (both important for forecasters and model developers) Systematic analysis of predictability of Alpine convective initiation on a 10-20 km scale (=>Towards replacing ALADIN by AROME as an input in INCA)