Tornadoes 2011 – Superoutbreak 2

Dr. Greg ForbesSevere Weather ExpertThe Weather Channel

2011 NWA Teacher’s Weather WorkshopBirmingham, AL

October 17, 2011

Radar echo of the SUPERCELL

(rotating) thunderstorm,spawning the EF4 tornado

at Tuscaloosa AL

Lavender-colored ball is due to debristossed aloft in the tornado

Strong radar return used tosimulate the tornado in 3D

Personal Damage Observations from April 27

• I flew in a helicopter over part of the Tuscaloosa tornado path and crossed part of another tornado path farther east

• I thought some of the structural damage in Tuscaloosa would have been F5 in the past(original Fujita Scale)

• The trees northeast of Tuscaloosa often fell inward TOWARD the tornado from the northeast; inflow winds before the strongest southwest winds arrived!

Tuscaloosa, AL

Before April 27

After April 27

EF-4

EF-0 EF-1

EF-1 to 2

EF-3

Tornadoes are ratedbased upon worst damage

Now using theEnhanced Fujita (EF) Scale

^^^Original

F-ScaleF

EnhancedFujitaScale

EFEngineers said F3 and higher windestimates were usually too high. Homes not built that strongly.

Enhanced Fujita Scale for Houses

Houses have “Achilles heels” that cause them to fail in winds weaker than 200 mph

EF4

EF3

EF3

EF2

EF2

EF0

EF1

Wind speeds are ESTIMATED afterwards based upon surveying damage using

Enhanced Fujita Scale

• 87% of tornadoes are Weak (EF0 and EF1)

• Strong (EF2 and EF3) and Violent (EF4 and EF5) tornadoes are less common but

cause 92% of deaths

Death rate is 50 to 100% greaterat night

Better initial home construction couldkeep EF1 from meaning “totally destroyed”

Need more in-home shelters to safe lives

Tuscaloosa AL Apartment Complex – southeast corner two-story apartments leveled (EF4, could have been F5)

apartment debristoward northeast

home debrisdown embankmenttoward northwest(inflow) EF3

trees converge

trees down from northeast(left-side inflow)

EF4+

EF0

EF2 -3

EF0- 1

Railroad bridge destroyed outside Tuscaloosa – no EF-Scale guidance on bridges

NWS-BMX

Hackleburg AL EF5 – brick home disintegrated

I never thought I’d see so many deaths from tornadoes as in 2011

Deadliest Known Tornado Years in USA1. 1925 – 7942. 1936 – 5523. 1917 – 551

4. 2011 – 546 (+ ?)5. 1927 – 5406. 1896 – 537

2011 had the deadliest tornadoes since 1957: Joplin MO (159)Hackleburg AL (72)Tuscaloosa AL (63)

April 2011 Tornado Outbreaks:

April 2011 Tornado Tally:

- 748 tornadoes - shattered old April record (267 in 1974)-broke record for any month (542 in May 2003)

2011 Tornado Tally:-about 1371 tornadoes through June 30 (record 1304 in 2008)- 546 killed from 57 killer tornadoes (most since 1936)- deadliest tornado (Joplin, MO on May 22 killed 159)

since 1947 (Woodard, OK, 181 killed)- Largest tornado outbreak on record (about 293 tornadoes, 4/26-28)

Factors in Tornado Formation

• Instability – needed to get intense thunder-storms to form; with low cloud bases

• Favorable winds and wind shear – winds turn clockwise and increase speed in lowest 3000 feet source of damaging winds, rotation

• A meteorological “trigger”: upper-air trough or jet streak, low-level convergence or front, etc. to help storms break through initial inhibition

PRIME TORNADO AREA – Large-scale factors

Supercell Thunderstorms:Strong Instability and Shear

(component)

(Component)

Tail Cloud, Independence, KS, 7/8/2008 – Dale Reynolds

Tail Wall cloud

Wall cloud

Classicsupercellthunderstorm

The worst tornadoes come from “supercells”

Thunderstorms that have large, long-lived rotating updrafts

Overshooting top – where the updraft reaches storm top

anvil

Very anomalous, persistentweather pattern in April 2011

Very warm from Ohio Valley to South

Strong and persistentjet stream and trough

2011 Superoutbreak (AL portion)

Joplin MO tornado – May 22, EF5, 159+ killed- Deadliest tornado in USA since 1947

April 26-28, 2011 Tornado Outbreak

Records (any outbreak)

293 tornadoes 316 deaths (second to

1925) 2900+ miles of path 67 tornadoes 400+ yds

wide 21 states hit

(numbers preliminary)

Ringgold, GA EF-4

Philadelphia EF-5

Rainsville EF-5

RainsvilleAL EF5

SmithvilleMS EF5 Hackleburg-

Phil CampbellAL EF5

MSEF5

Preliminary Comparison of Superoutbreaks – 1974 vs 2011(24 hours each)

*

*

**

Forbes’ Impact Index (100 max) 68.86 68.53 (next in line, 37.46)

Until 2011, the benchmarktornado outbreak was the

“Superoutbreak” of April 3-4, 1974

I studied the 1974 Tornado Superoutbreak with Dr. Fujita

148tornadoes24 hours

Multiple“suction”vortices

Yellow – Thunderstorms expectedRed – Severe thunderstorms possible

day of Yazoo City, MS EF4 TornadoApr 24, 2010

I developed TORCON in 2009to help inform people of tornado risk

TORCON – TORNADO CONDITIONS INDEX

• Scale of 0 to 10 (First 10 – north AL, 4/27/2011)• Multiply by 10 to get approximate probability of

a tornado within 50 miles (e.g., 5 50%)• Based upon forecasts of weather conditions

needed for tornado formation and how well they may come together

• Combines numerical model guidance, human expertise

Supercell Structure

Rear-flank downdraft

Tornado families

A supercellthunderstorm

often spawns asequence oftornadoes

called a“tornado family”

The gaps between tornadoes are usually downdraft-induced

So the storm-scale downdraft can create (and destroy) a tornado

“Classic” Mesocyclone Cycling tornado familyRelates to Rear-Flank Downdraft

Fujita and Forbes – tornado turns and hook echo evolution during

Superoutbreak

There Are Lots of Unknowns, Issues

• As few as 10% of supercells produce tornadoes• NWS Tornado Warning False Alarm Rate (FAR) is about

75% (2008)• NWS Tornado Warning Probability of Detection (POD)

about 72% (2008)• NWS Tornado Warning Lead Time 13+ min (2008)• Radar beam wider than tornado, overshoots sub-

cloud-base tornado at distances from radar Improvements if more radars?

Need more efficient warning system for peopleto receive warnings

Poor NEXRAD coverage below 1 km AGL

degraded tornado detection

Good meso detection

Denser network of low-powerlow-cost radars on cell

towers?

McLaughlin et al 2009: BAMS 90(12), 1797-1817

3 kmcoverage

1 km coverage

Recent Extreme Events – Global Warming?

• Feb 10, 2009 – Strongest and deadliest Feb OK tornado on record• Jan 7, 2008 – 2 WI tornadoes (Jan - only one previously)• Jan 7, 2008 – northern IL tornado (Jan – only one other

since 1950)• Jan 10, 2008 – EF1 tornado near Vancouver, WA (Jan –

only 2 previously since 1950)• Feb 5-6, 2008 Largest Feb outbreak on record; mid-South• Oct 18, 2007 – unprecedented killer tornado, northern MI• Dec 1, 2006 – 1st PA December tornadoes• Nov 1, 2000 – tornadoes near Bismarck, ND; farthest north

so late in year• Mar 11-13, 2006 – largest March outbreak• Sept 22, 2006 – largest non-tropical outbreak• Dec 29, 2006 – unprecedented TX Dec outbreak

Rare/Unprecedented Northern and Cold Season Events

Severe Weather and Global WarmingTrapp et al, 2007: Proc. Nat’l. Acad. Sci. 104(50), 19719-19723

MAM JJA

Difference in climate model parameters, 2072-2099 vs 1962-1989, RegCM3

NDSEV = # Severe T-storm days, whenCAPEx(0-6 km shear) at least 10,000

CAPE increases – warmer, moister, more unstable

Surface specific humidity increases

0-6 km shear mostly decreases

2 to 3 more days with severe thunderstormsNSDEV increases, up to 100% in South and East

Different results for different climate models

Strong upper trough and upper-level jet streak

Approaching frontal system;Warm moist air off Gulf of Mexico

Weather Maps, morning April 27, 2011

Tornado Winds are Estimated from Damage

Replaced by Enhanced Fujita EF Scale, 2/1/2007

(Original)

Fujita Scale (F0 to F5)F0 Damage, EF0 damage

Milestone Tap, Utica IL April 20, 2004

F3 to F4

EF3

EF3, Wheatland, WI, 1/7/2008 – Elizabeth Moore

Saved by a safe room, Wheatland, WI EF3, 1/7/2008 – Elizabeth Moore

Fujita Scale

F5 Damage in past, now often EF4