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PEC Departmental Safety Meeting March 2, 2010. Severe Weather Safety.

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Presentation on theme: "PEC Departmental Safety Meeting March 2, 2010. Severe Weather Safety."— Presentation transcript:

1 PEC Departmental Safety Meeting March 2, 2010

2 Severe Weather Safety

3 Severe Thunderstorms Considered severe if: Winds over 56 mph Hail 1 inch in diameter or larger Funnel cloud or tornado reported

4 Severe Thunderstorms May also include: Frequent lightning Flooding and/or flash flooding Downbursts

5 Severe Weather Season in Alabama Two severe weather seasons in Alabama: Primary: March through May Secondary: November & early December

6 Lightning Cloud-to-cloud lightning in Australia

7 Lightning Statistics

8 Lightning Safety Get indoors at first sounds of thunder If indoors, avoid: –Windows –Water sources –Telephone –Electrical appliances

9 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

10 Lightning Safety Unsafe areas include: –Canopies –Small picnic pavilions and rain shelters –Swimming pools –Open areas

11 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

12 Flooding Events

13 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

14 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

15 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

16 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

17 Tornadoes

18 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

19 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

20 Tornado Rating: F4 Damage – Lots of Debris

21 Tornado Rating: F5 Damage – Swept Clean

22 Super Cell Thunderstorms

23 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

24 Super Cell Thunderstorms




28 Tornado Vortex Signature (TVS) Base Reflectivity “Hook Echo”

29 TVS: Storm Relative Velocity Green – winds moving away from radar site Red – winds moving toward radar site

30 TVS Birmingham, April 8, 1998

31 TVS Enterprise, March 1, 2007

32 Tornado Activity in the U.S

33 Tornado Activity in the U.S.


35 Tornado Classification Tornadoes and funnel clouds form from wall clouds

36 Tornado Classification A funnel cloud has not yet reached the ground

37 Tornado Classification A wedge tornado is wider than tall Binger, OK

38 Tornado Classification A rope tornado near Tecumseh, OK

39 Tornado Classification A classic “funnel” tornado in Kansas

40 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

41 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

42 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)

43 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)

44 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)

45 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

46 Tornado Safety

47 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

48 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

49 Tornado Safety

50 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

51 Tornado Safety The polygon defines the actual warning area 5 counties are under a tornado warning

52 Tornado Safety Be aware of severe weather outlook risk category Use a NOAA storm radio for indoor warning Listen for sirens if outdoors

53 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

54 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)

55 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.

56 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

57 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

58 References

59 Questions? Left: F4 rated Palm Sunday Tornado in Calhoun Co. Right: Goshen UMC

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