The next SKYWARN meeting is 18-Aug @ 7:00 PM, the third Tuesday of the month.
About 21 members attended the 21-Jul meeting. Topics discussed included:
- Chris NŘCPG reviewed the EF scale and damage assessments.
- Lessons learned from the 17-Jun activation.
From Dave KCŘUVY
There were no activations during July.
Enhanced Fujita Scale
At the June meeting, Chris NŘCPG reviewed the Enhanced Fuji Scale (EF-Scale). Texas Tech University published a
recommendation for the EF Scale in 2004. The basis for the EF-Scale is to correlate Degree of Damage (DOD) with Damage Indicators (DI). The term "Damage Indicator" is a bit misleading in that it actually is a classification of structure types being analyzed. The DOD is a table of damage that can be seen for that specific type of DI. A range of wind speeds is associated with each DI and DOD.
From Minnesota WeatherTalk
It was ten years ago when one of the worst derechos (straight-line wind storms) to every hit the state. It started early in the day with damaging winds in the Fargo-Moorhead area (up to 91 mph), and then raced across the Iron Range and Boundary Waters Canoe Area of Minnesota. Millions of trees were blown down and some campers and canoeists were injured. Heavy rains accompanied this storm and followed in the aftermath of the wind damage. Some observers reported over 4 inches of rainfall. Hibbing Airport received 7.81 inches, while Marcell Forestry Station received 6.30 inches, and an observer in west central St Louis County reported over 8.8 inches. Obviously many roads were washed out and closed for a period of time.
VORTEX2 - Phase 1
From USA Today
The initial phase of Vortex2 started May 10 and ran through June 13. A second phase will run from May 1 through June 15 next year. Vortex2 is a two-spring experiment, because any one spring can be a bad year. About 120 people from 18 universities and government agencies traveled more than 11,000 miles during Vortex2's first phase, but found only a strong EF-3 tornado in far southeastern Wyoming that lasted about 30 minutes. It was the least number (of tornadoes) in that time period since the early 1990s, and only twice since World War II.
The topic of lightning safety was in the national news a lot this month. It was a big news story in the Metro resulting from the Stillwater teenager getting hit while playing under a tree. Here are nine myths of lightning safety from the NAtional Weather Service.
- MYTH: Lightning Never Strikes The Same Place Twice.
TRUTH: Lightning often strikes the same place repeatedly, especially if it’s a tall pointy isolated object. The Empire
State Building used to be used as a lightning laboratory, since it is hit nearly 25 times a year. Places prone
to lightning are places to avoid when thunderstorms are nearby!
- MYTH: If It’s Not Raining, Or If Clouds Aren’t Overhead, I’m Safe From Lightning.
TRUTH: Lightning often strikes more than three miles from the thunderstorm, far outside the rain or even
thunderstorm cloud. ‘Bolts From The Blue’, though infrequent, can strike 10-15 Miles from the thunderstorm.
Anvil lightning can strike the ground over 50 Miles from the thunderstorm, under extreme conditions.
Lightning in clouds has traveled over 100 miles from the thunderstorm.
- MYTH: Rubber Tires Protect You From Lightning In A Car By Insulating You From The Ground.
TRUTH: Lightning laughs at two inches of rubber! Most cars are reasonably safe from lightning. But it’s the metal
roof and metal sides that protect you, not the rubber tires. Thus convertibles, motorcycles, bicycles, open
shelled outdoor recreational vehicles, and cars with plastic or fiberglass shells offer no lightning protection.
Likewise, farm and construction vehicles with open cockpits offer no lightning protection. But closed cockpits
with metal roof and sides are safer than going outside. And don’t even ask about sneakers! ?
- MYTH: A Lightning Victim Is Electrified. If You Touch Them, You’ll Be Electrocuted.
TRUTH: The human body doesn’t store electricity. It is perfectly safe to touch a lightning victim to give them first aid.
This is the most chilling of lightning myths. Imagine someone dying needlessly, for want of simple CPR or
mouth-to-mouth resuscitation, when their chances of survival was ~90%!
- MYTH: If Outside In A Thunderstorm, Go Under A Tree To Stay Dry.
TRUTH: Being underneath trees is the second leading activity for lightning casualties – enough said?!
- MYTH: I’m In A House, I’m Safe From Lightning.
TRUTH: While a house is a good place for lightning safety, just going inside isn’t enough. You must avoid any
conducting path leading outside, such as corded telephones, electrical appliances, wires, TV cables,
plumbing (including plastic pipes with water in them), metal doors or window frames, etc. Don’t stand near a
window to watch the lightning. An inside room is generally best.
- MYTH: When Playing Sports And Thunderstorms Threaten, It’s Okay To Finish The Game Before Seeking Shelter.
TRUTH: Sports is the activity with the fastest rising rate of lightning casualties. No game is worth death or life-long
severe injury. All people associated with sports should have a lightning safety plan and stick to it strictly.
Seek proper shelter immediately when lightning threatens. Adults are responsible for the safety of children!
- MYTH: Structures With Metal, Or Metal On The Body (Jewelry, Watches, Glasses, Backpacks, Etc.), Attract Lightning.
TRUTH: Height, pointy shape, and isolation are the dominant factors controlling where a lightning bolt will strike. The
presence of metal makes virtually no difference on where lightning strikes. Mountains are made of stone, but
receive many strikes each year. When lightning threatens, take proper protective action immediately. Don’t
waste time shedding metal off your body, or seeking shelter under inadequate structures. But while metal
doesn’t attract lightning, touching or being near long metal objects (fences, railings, bleachers, vehicles, etc.)
is still unsafe when thunderstorms are nearby. If lightning does happen to hit it, the metal can conduct the
electricity a long distance (even over 100 yards) and still electrocute you.
- MYTH: If Trapped Outside And Lightning Is About To Strike, Lie Flat On The Ground.
TRUTH: This advice is decades out of date. Better advice is to use the ‘Lightning Crouch’: put your feet together,
squat low, tuck your head, and cover your ears. Lightning induces electric currents along the top of the
ground that can be deadly over 100 Feet away. While lying flat on the ground gets you as low as possible,
which is good, it increases your chance of being hit by a ground current, which is bad. The best combination
of being low and touching the ground as little as possible is the ‘Lightning Crouch’. But the ‘Lightning
Crouch’ should be used only as a last resort. Much better would be to plan outdoor activities around the
weather to avoid thunderstorm exposure and to have proper shelter available.
- MYTH: Go near a tall pointy isolated object when thunderstorms threaten, to be within the 45° “cone of protection”.
TRUTH: The “cone of protection” is a myth! While tall pointy isolated objects are statistically more likely to be struck
by lightning, it’s not nearly reliable enough to rely on for safety. Lightning can still strike you near the tall
object. Besides, the lightning electricity will likely spread out along the surface of the ground and can still kill
you over 100 Ft from the “protecting” object. Also, if you are close to or touching the tall object, you can be
electrocuted via side flash or contact voltage. NO PLACE OUTSIDE IS SAFE NEAR A THUNDERSTORM!
What is Lightning?
From Science Daily
Lightning is a form of static electricity. We experience static electricity every time we drag our feet on a carpet and then touch a conducting surface, like a metal doorknob. The shuffling causes our bodies to pick up extra electrons. Touching something with a positive charge, like metal, causes the electrons to "jump" across the small gap from our fingers to the object, and we experience a tiny electric shock. Similarly, lightning occurs because clouds become negatively charged as the water droplets inside rub up against each other during the natural process of evaporation and condensation, when moisture accumulates in the clouds. This charge seeks out something with a positive charge -- the ground, ideally -- and the lightning is the "spark" closing the gap between the two.
As more and more water droplets collide inside a cloud, the friction between them produces enough extra energy to knock off electrons. The ousted electrons gather at the lower portion of the cloud, giving it a negative charge. Eventually the charge becomes so intense that electrons on the Earth's surface are repelled by the growing negative charge and burrow deeper into the Earth. The Earth's surface becomes positively charged, and hence very attractive to the negative charge accumulating in the bottom of the cloud. All that is needed is a conductive path between cloud and Earth, in the form of ionized air -- another byproduct of the collision process. When the two charges finally meet, current jumps between the earth and the cloud, and the result is lightning.
Term For The Month
From USA Today
Commercial aircraft cruise at altitudes in excess of 30,000 feet. Hot air exhausted from jet engines mix with cold air, forming clouds known as condensation trails, or contrails. When the atmosphere is close to saturation, the particulate matter in the exhaust can provide nucleation sites where ice crystals can form. The same process occurs when you are able to see your breath on a chilly day.