1. The Lone Grove, OK, Tornado 10/02/2009 Robert Warren

2. Case Study: The Lone Grove Tornado Dallas Oklahoma City February 10, 2009 – EF4 tornado passed through Lone Grove, OK 8 people killed; $3million worth of damage

3. SPC Day 4–8 Convective outlook on Saturday, February 7 th : “…INCREASING CONVECTIVE POTENTIAL…INCLUDING A CONSIDERABLE RISK FOR SEVERE STORMS. THIS MAY COMMENCE LATE TUESDAY AFTERNOON ACROSS PARTS OF THE SOUTHERN PLAINS…” SPC Day 3 Convective outlook on Sunday, February 8 th : “…LONG HODOGRAPHS WITH LARGE LOW-LEVEL CLOCKWISE CURVATURE WILL BE QUITE FAVORABLE FOR SUPERCELLS CAPABLE OF PRODUCING TORNADOES…” SPC forecasts

4. SPC Day 1 Convective outlook on Tuesday, February 10th: “…GREATER SEVERE WEATHER THREAT IS EXPECTED TO DEVELOP ALONG THE DRY LINE IN CENTRAL OK TO CENTRAL TX BY LATE AFTERNOON… STRENGTHENING OF THE SLY LLJ /50+ KT/ FROM E TX/LA TO ERN KS/MO WILL RESULT IN LARGE CURVED HODOGRAPHS AND THE LIKELIHOOD FOR STRONG/SIGNIFICANT TORNADOES…” SPC forecasts

5. SPC Day 1 Convective outlook on Tuesday, February 10th: “…THE STRONG LOW-LEVEL SHEAR AND MOIST LOW LEVELS WILL SUPPORT THE POSSIBILITY OF A FEW LONG-TRACK SUPERCELLS WITH STRONG TORNADOES LATE THIS AFTERNOON INTO EARLY TONIGHT ACROSS THE MDT RISK AREA…” Forecast update

6. Skew-T for Dallas – 6am

7. Visible Satellite – 12:45pm

8. Surface Analysis – 1pm

9. CAPE and CIN – 1:00pm

10. Driving West near Lone Grove – 1:37pm

11. Lone Grove Our location Tornadoes in central Oklahoma – 3:05pm

12. Visible Satellite – 4:33pm

13. Skew-T for Dallas – 6pm

14. 500mb geopotential height & wind – 6pm

15. Storm Motion and SRH – 6:00pm

16. Significant Tornado Parameter & CIN – 6:00pm

17. Surface analysis – 6:00pm

18. Wall Cloud near Bellevue, TX – 6:05pm

19. Doppler Velocities – 6:05pm

20. “THIS SIGNIFICANT WEATHER ADVISORY IS FOR JEFFERSON AND LOVE COUNTIES. A SEVERE THUNDERSTORM WAS LOCATED 16 MILES SOUTHWEST OF OSCAR AT 620 PM CST...MOVING NORTHEAST AT 40 MPH. THIS STORM HAS BECOME BETTER DEVELOPED OVER THE PAST 15 MINUTES. A TORNADO WARNING IS IN EFFECT FOR MONTAGUE COUNTY IN NORTH TEXAS. A SEVERE THUNDERSTORM WARNING WILL LIKELY BE REQUIRED AND POSSIBLE A TORNADO WARNING OVER THE NEXT 30 MINUTES.” Significant Weather Advisory – 6:20pm

21. Updraught lightning – 6:20pm

22. Doppler Velocities – 6:22pm

23. Rope tornado – 6:31pm

24. Indicative of large hail 3-body scatter process –Portion of radar beam is scattered towards surface –Portion of this is scattered back into the cloud –Portion of this is scattered back to the radar Delay in return signal → radar ‘sees’ target at a greater distance Doppler velocity can be used to infer fall speeds of hail Hail Spike – 6:31pm

25. Threat Net – 6:39pm

26. “AT 650 PM CST...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A SEVERE THUNDERSTORM CAPABLE OF PRODUCING A TORNADO 7 MILES SOUTHEAST OF GRADY...MOVING NORTHEAST AT 40 MPH.” Tornado Warning – 6:50pm

27. “AT 731 PM CST… DOPPLER RADAR AND STORM SPOTTERS OBSERVED A TORNADO NEAR LONE GROVE… MOVING NORTHEAST AT 35 MPH…” Tornado Confirmed – 7:31pm

28. Velocity Aliasing (folding) on the Doppler radar. Doppler Dilemma – trade-off between maximum Doppler velocity and maximum range “AT 738 PM CST…A LARGE…VIOLENT TORNADO WAS LOCATED IN THE NORTHWEST PARTS OF ARDMORE…MOVING NORTHEAST AT 40 MPH…” “Violent Tornado” – 7:38pm

30. Lasted over an hour & travelled 35 miles Reached peak intensity of EF4 just before it hit Lone Grove Tornado track

31. Mesonet – network of automated weather stations across OK Newport site < 2 miles north of tornado track As storm passed: Sharp temperature and dewpoint drop Northwesterly wind gust of 58 mph Marked pressure drop Heavy rain associated with storm core Mesonet Meteorgram

32. SPC Storm Reports

33. 8 people killed (7 in Lone Grove, and one truck driver on I-35) 14 seriously injured 114 residences destroyed (including 2 trailer parks) Cars and RVs overturned Metal forced through trees Double storey houses reduced to single storey Loss of household possessions $3million worth of damage Damage

34. National Guard sent to provide security American Red Cross and Salvation Army shelters set up Local charities, churches schools offer money, shelter, food and support to the victims Help with the clean up from groups across the state President Obama approved federal assistance on the 15 th FEMA set up a disaster recovery centre on the 20 th Response

35. Why was the death toll so high? Event was well forecast – risk identified several days early Numerous watches, warnings, and advisories issued on the day So why was the death toll so high? Tornado sirens: Many people said they went off only a few seconds before it struck Complacency: “I wasn’t worried. It was February. We don’t get tornadoes like this in February.” – Sherry Franks, Lone Grove survivor After dark