PEC Departmental Safety MeetingMarch 2, 2010

Severe Weather Safety

Severe Thunderstorms

Considered severe if:

• Winds over 56 mph

• Hail 1 inch in diameter or larger

• Funnel cloud or tornado reported

Severe Thunderstorms

May also include:• Frequent lightning

• Flooding and/or flash flooding

• Downbursts

Severe Weather Season in Alabama

Two severe weather seasons in Alabama:

• Primary: March through May

• Secondary: November & early December

Lightning

Cloud-to-cloud lightning in Australia

Lightning Statistics

Lightning Safety

• Get indoors at first sounds of thunder

• If indoors, avoid:– Windows– Water sources– Telephone– Electrical appliances

Lightning Safety

• If caught outdoors:

– Get inside a vehicle if possible

– Get to lower ground

– Get away from tall objects (trees, poles, other people, etc.)

– Crouch down with feet together

Lightning Safety

• Unsafe areas include:

– Canopies

– Small picnic pavilions and rain shelters

– Swimming pools

– Open areas

Lightning Safety• If planning outdoor events be prepared.

– Know the local forecast– Have a weather plan ready to activate

• Suspend outdoor activities until 30 minutes after last report of thunder

• Victims of lightning strike do not carry a charge and first aid may be administered as soon as practical

Flooding Events

Flooding Events

• Flooding is an excessive accumulation of water that submerges normally dry land

• May include “regular” floods or flash floods

• More people die annually as a result of floods than lighting, hurricanes, or tornadoes

Flood vs. Flash Flood• Flood – Generally a long-term event that centers

around a river, creek, or other watercourse

• A flood may not peak for days after a heavy rain

• May result from heavy rains upstream from the affected areas

• Classified as a flood if duration is longer than 6 hours

Flood vs. Flash Flood• Flash Flood – Occurs quickly when low areas cannot

quickly drain after a torrential rain

• May occur away from normal water courses

• May occur when a water barrier (dam or levee) fails

• May have little or no warning

• Classified as a flash flood if duration is less than 6 hours

Flood Safety

• Get to high ground

• Stay out of basements

• Do not drive through flowing water. Water 6” deep can sweep you off your feet

• Do not let children play in ditches after a rain storm

Tornadoes

Tornadoes

• Wind speeds ranging from 40 to greater than 300 mph

• Range from several yards in width to more than 2 miles

• May stay on the ground for a few feet or dozens of miles

Tornado Rating System

• Old “F-scale” (Dr. Ted Fujita, 1971) was based solely on visual damage assessment

• New “EF-rating” (Enhanced Fujita, 2007) based on damage assessment, radar measured wind speed, and structural strength of buildings damaged

Tornado Rating:F4 Damage – Lots of Debris

Tornado Rating:F5 Damage – Swept Clean

Super Cell Thunderstorms

Super Cell Thunderstorms

• Usually isolated from other thunderstorms – form out ahead of the “squall line”

• Characterized by a deep, rotating updraft called a mesocyclone

• Responsible for generating most tornadoes

Super Cell Thunderstorms

Super Cell Thunderstorms

Super Cell Thunderstorms

Super Cell Thunderstorms

Tornado Vortex Signature (TVS)Base Reflectivity

“Hook Echo”

TVS: Storm Relative Velocity

• Green – winds moving away from radar site• Red – winds moving toward radar site

TVSBirmingham, April 8, 1998

TVSEnterprise, March 1, 2007

Tornado Activity in the U.S

Tornado Activity in the U.S.

Tornado Activity in the U.S.

Tornado Classification

• Tornadoes and funnel clouds form from wall clouds

Tornado Classification

• A funnel cloud has not yet reached the ground

Tornado Classification

• A wedge tornado is wider than tall• Binger, OK

Tornado Classification

• A rope tornado near Tecumseh, OK

Tornado Classification

• A classic “funnel” tornado in Kansas

Notable National Tornadic Events

• Deadliest in U.S. History – Great Tri-state tornado of 1925 (Missouri, Illinois, Indiana)– 695 confirmed fatalities– 219 mile damage path (longest in world)– Estimated ground speed of 73 mph

Notable National Tornadic Events

• Super Outbreak (April 3-4, 1974)– Largest tornado outbreak in history for a 24

hour period– Extremely rare meteorological conditions– 330 confirmed fatalities

Notable Alabama Tornadic Events

• April 3-4, 1974 – Super Outbreak produces three F5 tornadoes (Guin, Mount Hope, Tanner) (23 killed in Guin)

• April 4, 1977 – F5 tornado hits North Smithfield Subdivision near intersection of Daniel Payne Drive and I-65 (22 killed)

Notable Alabama Tornadic Events

• March 27 1994 – F4 “Palm Sunday Tornado” destroys Goshen United Methodist Church in Cherokee County during morning services (22 killed)

• April 8 1998 – F5 tornado carves a 31 mile path through Oak Grove, Sylvan Springs, Rock Creek, Maytown, Edgewater, and McDonald Chapel (34 killed)

Notable Alabama Tornadic Events

• April 27, 2011– Major tornado outbreak in Southern United States.

• EF4 Tornadoes common across North and Central Alabama including Tuscaloosa to Birmingham, Blountsville, Cullman, Shoal Valley, Elmore County, and Rainsville Tornadoes (all EF4)

• Hackleburg hit by EF5 (first since 1998)

Tornado Safety

• The National Storm Prediction Center (SPC) in Norman, OK issues 1, 2, and 3 day outlooks and assigns a “risk category”– Slight Risk (4 or 5 times a year) – severe

thunderstorm development expected, but relatively low coverage

– Moderate Risk (1 or maybe 2 times a year) – like low risk, but with increased coverage & intensity

– High Risk (rare) – used when a major outbreak is expected

Tornado Safety

Tornado Safety

• A Tornado Watch is issued when conditions are favorable for tornado development

• A Tornado Warning is issued when a tornado has been detected by radar or sighted by storm spotters

• Tornadoes form quickly so you may have less than 10 minutes to execute your plan

Tornado Safety

• Watches are issued by the SPC for a broad area

• Watches are issued on a county by county basis

• Watches are intended to encourage the general public to be alert to the possibility of changing conditions

Tornado Safety

Tornado Safety• Warnings are issued by the local NWS office

• A warning means a tornado has been detected by Doppler Radar or has been sighted by a storm spotter

• Only the NWS can issue watches and warnings – local news media simply report

• BHM NWS office is located at the Shelby County Airport in Calera

Tornado Safety

• The polygon defines the actual warning area• 5 counties are under a tornado warning

Tornado Safety

• Be aware of severe weather outlook risk category

• Use a NOAA storm radio for indoor warning

• Listen for sirens if outdoors

Tornado Safety

• Following are the best places to shelter during a tornado:– Basement– Interior hallway or closet– Bathtub (bring a mattress to cover you if you can)– Get under a workbench or sturdy piece of

furniture– In high rise office buildings, go to an interior

stairwell

Tornado Safety

• Following are the worst places to be during a tornado:– Vehicle– Mobile home or trailer– Out in the open (get to a ditch or the low

place)– Under a highway overpass (winds increase in

the tight spaces)

Tornado Myths:True or False?

• Tornadoes can’t cross a river– False: wind can actually increase

• Tornadoes can’t cross mountains– False: tornadoes are columns of air that come from above.

• Tornadoes can rotate clockwise or counter-clockwise– True: Anti-cyclonic (clockwise) tornadoes occur very rarely.

Tornado Myths:True or False?

• Tornadoes can come from any direction– True: although most travel from southwest to northeast

• Tornadoes occur only during tornado season– False: tornadoes have occurred during every month

• The size or shape of a tornado is not an indication of its strength– True: large tornadoes may be relatively weak, while thin

“rope” tornadoes can be extremely violent

Tornado Myths:True or False?

• The strongest tornadoes in Alabama occur only during night-time hours– False: Violent F4 and F5 twisters have occurred

in Alabama during the middle of the day

• Tornadoes in Alabama are harder to see than those in the Midwest– True: More hills, more tall trees, more rain

around the tornado

References

• www.lightningsafety.com• www.wikipedia.org• www.nws.noaa.gov• www.talkweather.com• www.abc3340.com/weather

Questions?

• Left: F4 rated Palm Sunday Tornado in Calhoun Co.• Right: Goshen UMC