Nowcasting Challenges and Lessons from Beijing 2008 Forecast Demonstration Project

1. Beijing 2008 Forecast Demonstration Project Hong Kong CN Can AUS CN CN Can Can US Can US CN CN

4. Nowcasting challenges during B08FDP; Implications for nowcasting systems Jim Wilson Talk subjects • Review 2006 and 2007 forecast challenges • Nowcasting challenges during the FDP • Implications for nowcasting systems in the future

5. Lessons from 2006 and 2007 for nowcasting convective storms in Beijing • The mountains to the west and north are major influences on convective • storm evolution • - often dissipation in moving from mountains to plains • - initiation along the foothills • - initiation over Beijing • - initiation along local convergence lines

6. Initiation by high terrain Foothills dissipation/growth City Initiation Foothill initiation Nowcasting lessons from 2006-7

7. Primary Forecast Challengees Boundary Initiation

8. Lessons from 2006 and 2007 for nowcasting convective storms in Beijing • The mountains to the west and north are major influences on convective • storm evolution • - often dissipation in moving from mountains to plains • - initiation along the foothills • - initiation over Beijing • - initiation along local convergence lines • Extrapolation often fails even at 1 hour • Numerical models often do a poor job of capturing the small scale • influences on storm evolution • Effective nowcasting requires monitoring of localized boundary layer • convergence lines, upslope wind component, stability, cumulus cloud • growth and storm evolution.

9. CHALLENGECASES During B08FDP 2 Aug – Thunderstorms threaten rehearsal for opening ceremony 8 Aug – Thunderstorms threaten opening ceremony 10 Aug – Large scale rain, challenge to forecast end 14 Aug – Rapid thunderstorm development impact games 21 Aug – bands of convective storms threaten games 24 Aug – Thunderstorms threaten closing ceremony

10. Aug 8, 2008 Opening Ceremony Thunderstorms moving toward the stadium Olympic Stadium

11. 10 Aug. Heavy rain over venues, When will it end?

12. 14 Aug. Initiation of heavy rain over Beijing and venues 1100 AM 1400 PM 1100 AM local Heavy rains Will begin in city Within 75 min. 1100 AM local 1230 APM

13. 21 Aug. Rain band moving from northwest

14. 24 Aug. Thunderstorm Triple Threat for Closing Ceremony Time 1500 local 2. Mountain thunderstorms moving east 1.Model forecasting Precipitation over Beijing from 1700-2000 local 3. Boundary layer Convergence line

15. B08FDP Nowcast challenge on 2 Aug. Opening ceremony rehearsal Area of mountain thunderstorms moving from NW toward Beijing

16. B08FDP Nowcast challenge on 2 Aug. Opening ceremony rehearsal Aug 2 ~ 15 local Rehearsal for Opening Ceremony starts In 2 hours (1700 local) Forecast No Storms Will effect the Bird Nest 2+hr lead time

17. WRF/RUC forecast for 16, 17 and 18 local Forecasting very little precipitation and does not resemble actual situation. However it does not forecast any precipitation on plains

18. Grapes-Swift 2-hr Extrapolation for 1800 local Extrapolation: rain moving very slow toward stadium Stadium

19. Grapes-Swift 2-hr Blend for 1800 local Rapidly moved Rain past the stadium Stadium

20. Extrapolation Nowcasts for 16, 17 and 18 local Forecasts rain over stadium between 17 and 18 local

21. Human modification of extrapolation forecast for 1800 local Dissipates storms over plains. No rain over stadium.

22. Aug 2 Rehearsal for Opening Ceremony Forecast No Storms Will effect the Bird Nest 3+hr lead time

37. Extrapolation Nowcasts for 18 local Forecasts rain over stadium between 17 and 18 local

38. Human modification of extrapolation forecast for 1800 local Skill Score is ZERO Dissipates storms over plains. No rain over stadium.

39. Why did the human forecast no rain ? 1) Storms only moderately organized, frequently will dissipate in moving to plains

40. Why did the human forecast no rain ? 1) Storms only moderately organized, frequently will dissipate in moving to plains 2) Sounding stable CIN -87, CAPE 91

41. Beijing sounding released at 1300 local CIN -87j/kg CAPE 91 j/kg Sounding Corrected for Dry bias

42. Why did the human forecast no rain ? 1) Storms only moderately organized, frequently will dissipate in moving to plains 2) Sounding stable CIN -87, CAPE 91 3) Surface stations show moisture same as 1300 local sounding 4) Satellite shows no cumulus over plains clouds even along sea breeze

44. Why did the human forecast no rain ? 1) Storms only moderately organized, frequently will dissipate in moving to plains 2) Sounding stable CIN -87, CAPE 91 3) Surface stations show moisture same as 1300 local sounding 4) Satellite shows no cumulus over plains clouds even along sea breeze 5) Radar shows no cumulus over plains

45. 02 Aug 2008 02-14 UTC Radar tracks of >35 dBZ cells

46. Summary • Great Data Set: 3 years high resolution data provide nice examples of meaningful • nowcasting challenges in a large city under high impact situations • Extrapolation Inadequate: nowcasts even at 1 hour were often not useful and significant • differences could occur between systems. • Models Inadequate: Three rapid update, high resolution, 3DVAR models available. • None assimilated high resolution radar data. Significant problems handling • convection. • Blending on Hold : Personally feel not useful until have radar data assimilation • Nowcasting Success: Regardless of difficulties with automated systems nowcasts • were good because of human forecaster • Demonstrates importance of : high resolution observations, good forecast • tools, knowledge of local environment and ROLE OF FORECASTER • More then anything else B08FDP demonstrated the value of having real-time • nowcasting experiments with international participation

48. Xie Xie

49. THANK YOU

50. Beijing 2008 Forecast Demonstration Project Hong Kong CN Can AUS CN CN Can Can US Can US CN CN