1. Large-scale context for the UK floods in Summer 2007 Submitted to Weather, 14 May 2008 Mike Blackburn 1 John Methven 2 and Nigel Roberts 3 (1) National Centre for Atmospheric Science, University of Reading (2) Department of Meteorology, University of Reading (3) Met Office, Joint Centre for Mesoscale Meteorology

2. Summer 2007 and UK Flooding Outline: UK and European regional rainfall Global context: evolution and averages Synoptic development for 3 rainfall events: Upper-air precursors Synoptic structure and rainfall Warm air-mass trajectories

3. England-Wales Rainfall (Mar-Aug 2007) May-July record rainfall : 216% of 1961-1990 average

4. European Precipitation (% of normal) JuneAugustJuly May-July

5. Large-scale evolution: z250 anomaly 45N-60N 15 June 25 June 20 July

6. Jet streams (isotachs, 250hPa) 12 June – 25 July average Anomaly 2007Climatology (ms -1 )

7. Jet streams (isotachs, 250hPa) 12 June – 25 July average (ms -1 )

8. Streamfunction anomaly 12 June – 25 July average Upper troposphere : = 0.200 Lower troposphere : = 0.850 (m 2 s -1 )

9. Sea Surface Temperature 12 June – 25 July average OLR 12 June – 25 July average Anomaly - NCEP reanalysis data Anomaly - NOAA interpolated data (Wm -2 ) (K)

10. SST indices Niño 3.4 weakly negative in June-July

11. Circumglobal teleconnections Ding & Wang (2005, J.Climate) Hemispheric teleconnection pattern Associated with Indian Summer Monsoon variability correlates with SST (La Nina), due to effect on ISM Note Atlantic/European pattern changes through summer season

12. ENSO composites Ding & Wang (2005, J.Climate)

13. Monsoon – all-India rainfall

14. 15 June rainfall θ(pv2) Fri 15 th 00utc Wed 13 rd 00utc Tue 12 nd 00utc Thur 14 th 00utc

15. 15 June rainfall event Fri 15 th 00utc Wed 13 rd 00utcTue 12 nd 00utc Thur 14 th 00utc

16. 15 June rainfall event PV on θ=315K θ w on 850hPa msl pressure Heavy showers Heavy continuous rain

17. 15 June rainfall event

18. 25 June rainfall θ(pv2) Mon 25 th 00utc Sat 23 rd 00utc Fri 22 nd 00utc Sun 24 th 00utc

19. 25 June rainfall event Mon 25 th 00utc Sat 23 rd 00utcFri 22 nd 00utc Sun 24 th 00utc

20. 25 June rainfall event PV on θ=315K θ w on 850hPa msl pressure Heavy showers Heavy continuous rain

21. 25 June rainfall event

22. 20 July rainfall θ(pv2) Fri 20 th 00utc Weds 18 th 00utc Tues 17 th 00utc Thurs 19 th 00utc

23. 20 July rainfall event Fri 20 th 00Z Weds 18 th 00ZTues 17 th 00utc Thurs 19 th 00Z

24. 20 July rainfall event PV on θ=315K θ w on 850hPa msl pressure Heavy showers Heavy continuous rain

25. 20 July rainfall event

26. Herstmonceux sounding 00utc 20 July Column water vapour

27. Herstmonceux sounding 12utc 20 July

28. Weather system schematic for extreme rainfall (2004)

29. Summary: Soil moisture pre-conditioned (May rain) Persistent large-scale pattern, June-July Jet displacement associated with hemispheric wave pattern Quasi-stationary UK upper trough forcing from upper levels slow-moving weather systems 3 major UK rainfall events Warm air-mass origin over subtropical Atlantic Cool SST anomalies south & west of UK Air was warm & moist due to location of origin