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

The Lone Grove, OK, Tornado 10/02/2009

Robert Warren

Case Study: The Lone Grove Tornado

DallasOklahoma City

• February 10, 2009 – EF4 tornado passed through Lone Grove, OK• 8 people killed; $3million worth of damage

• SPC Day 4–8 Convective outlook on Saturday, February 7th:“…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 8th:“…LONG HODOGRAPHS WITH LARGE LOW-LEVEL CLOCKWISE CURVATURE WILL BE QUITE FAVORABLE FOR SUPERCELLS CAPABLE OF PRODUCING TORNADOES…”

SPC forecasts

• 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

• 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

Skew-T for Dallas – 6am

Visible Satellite – 12:45pm

Surface Analysis – 1pm

CAPE and CIN – 1:00pm

Driving West near Lone Grove – 1:37pm

Lone GroveOur location

Tornadoes in central Oklahoma – 3:05pm

Visible Satellite – 4:33pm

Skew-T for Dallas – 6pm

500mb geopotential height & wind – 6pm

Storm Motion and SRH – 6:00pm

Significant Tornado Parameter & CIN – 6:00pm

Surface analysis – 6:00pm

Wall Cloud near Bellevue, TX – 6:05pm

Doppler Velocities – 6:05pm

“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

Updraught lightning – 6:20pm

Doppler Velocities – 6:22pm

Rope tornado – 6:31pm

• 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

Threat Net – 6:39pm

“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

“AT 731 PM CST… DOPPLER RADAR AND STORM SPOTTERS OBSERVED A TORNADO NEAR LONE GROVE… MOVING NORTHEAST AT 35 MPH…”

Tornado Confirmed – 7:31pm

• 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

• Lasted over an hour & travelled 35 miles• Reached peak intensity of EF4 just before it hit Lone Grove

Tornado track

• 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

SPC Storm Reports

• 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

• 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 15th

• FEMA set up a disaster recovery centre on the 20th

Response

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