By USACRC Knowledge Magazine StaffMarch 20, 2017
FORT RUCKER, Ala. (March 20, 2017) - The welcome relief from the bitter cold and snow of winter brings with it another significant hazard - the spring and summer severe weather conditions. It is crucial all Soldiers are familiar with the inherent dangers of severe weather.
Often called nature's heat engine, thunderstorms are born from cumulus clouds that grow into towering cumulus and, ultimately, reach adulthood as cumulonimbus. While thunderstorms can occur any time of year, they most often occur in the late afternoon to early evening on hot summer days. They can form by themselves (single cell, super cell or air mass) or in clusters (frontal, squall lines or mesoscale convective complexes). A thunderstorm develops in three stages - the cumulus or developing stage, the mature stage and the dissipating stage - and can harness energy equal to, and often greater than, the energy released by an atomic bomb.
Microbursts are well-documented hazards known for bringing down aircraft. They are small-scale, intense downdrafts that, upon reaching the surface, spread outward in all directions. The greatest threat from these downdrafts often occurs along the front or leading edge of a thunderstorm. Because of their small size (less than one to two and a half miles) and their short lifespan (usually less than 15 minutes), downdrafts most often occur over areas without surface precipitation.
Microbursts are not easily detectable using conventional weather radar or wind shear alert systems. The intensity of the downdraft can reach 100 feet per second. Horizontal winds near the surface can be as strong as 45 knots, resulting in a 90-knot shear (headwind to tailwind change for a traversing aircraft) across the microburst. A major consideration for pilots is that a microburst will intensify for about five minutes after it strikes the ground.
Hail is regarded as one of the most serious aviation hazards associated with thunderstorms. It is usually found between 10,000 and 15,000 feet above ground level, with the greatest frequency of hail occurring during the mature stage of a thunderstorm. Hail can also be found as far as five miles outside and ahead of an advancing thunderstorm and can produce serious structural damage to an aircraft in just a few seconds.
Lightning, in the United States, there are an estimated 25 million lightning flashes each year. During the past 30 years, lightning killed an average of 62 people per year. Lightning can strike not only people on the ground; it can also strike the skin of an aircraft and its electronic components. Lightning generally occurs within 5,000 feet of the freezing level, in light precipitation or light to negligible turbulence. Lightning "crawlers" can travel more than 35 miles along the clouds and have been observed out to 75 miles on radar.
Tornadoes are nature's most violent storms. Although tornadoes happen year round, the two peak seasons in the United States are spring (March through May) and fall (November). Spawned from powerful thunderstorms, tornadoes can cause fatalities and devastate a neighborhood in seconds. A tornado appears as a rotating, funnel-shaped cloud that extends from a thunderstorm to the ground with whirling winds that can reach 300 mph. Damage paths can be in excess of one mile wide and 50 miles long. Most tornadoes travel from southwest to northeast and occur during the late afternoon through early evening. When tornado watches or warnings are issued for the area, take immediate safeguards.
Turbulence is the greatest meteorological danger to aviation. It is caused by the tremendous updraft and downdraft winds within the thunderstorm. The most severe turbulence is located between 8,000 and 15,000 feet AGL within the updraft. Updraft winds can be greater than 65 feet per second. Downdraft winds also can produce turbulence, but they are usually less severe and occur below 10,000 feet AGL. Downdrafts have been known to slam a plane into the ground while landing.
Icing is another significant hazard associated with thunderstorms. Although it can occur during all three stages of a thunderstorm, icing generally occurs in the mature and dissipating stages when temperatures are between zero and minus 15 C. Supercooled water that exists at subfreezing temperatures will freeze on contact with an aircraft. Clear icing can quickly become extremely hazardous.
Flooding and Flash Flooding, according to the National Oceanic and Atmospheric Administration, flooding is the No. 1 weather-related cause of death with about 140 deaths in the United States each year. Nearly half of all flash-flood fatalities are auto-related. Understanding the dangers of flooding and flash flooding and knowing the immediate actions to take can save lives.
• Seek higher ground immediately.
• Avoid small rivers and streams; dry riverbeds and low spots can also fill rapidly.
• Do not walk through flowing water more than ankle deep.
• Do not allow children to play around streams, drainage ditches or viaducts, storm drains or other flooded areas.
• If in a vehicle, do not drive through flooded areas.
o The large majority of deaths due to flash flooding are due to people attempting to drive through flooded areas.
o Two feet of water can easily carry most vehicles away.
o Roadways concealed by flood waters may not be intact.
o Most flash-flood fatalities occur at night, and most victims become trapped in their automobiles.
Hurricanes, among the many significant summertime phenomena are hurricanes. The Atlantic hurricane season runs from June 1 through Nov. 30. The storms develop as a tropical wave and mature into hurricanes over a period of days. Warm surface waters and a lack of shear in the upper levels of the atmosphere aid in the development of hurricanes.
The storm surge is the most dangerous part of a hurricane. Storm surge is a great dome of water often 50 miles wide or greater that sweeps across the coastline ahead and east of the eye of the hurricane. Hurricanes will also spawn tornadoes, most often found in the right-front quadrant (ahead and to the east of the eye) of the storm, roughly 50 to 300 miles from the center.
In the combat zone, much of the same weather found in the United States can also be found in theater. Convection and rainfall tend to fall off during the summer months, thus making it much drier in these regions. Additional features that affect the Middle East are the Shamal, found over Iraq and the Arabian Peninsula, and the Seistan - or "Wind of 120 Days - over Eastern Iran and the "Stans" region. These are areas of significant winds and blowing dust and/or sand. These strong, northwesterly wind events sweep across the region beginning in May and lasting throughout the summer months. They develop when strong cold fronts pass over the mountains of Turkey and Kurdistan and the leading edge of a mass of relatively cooler air kicks up dust and sand, sending it aloft.
The duration of Shamals or Seistans is normally three to five days. Since the resultant dust and sandstorm is several thousand feet deep, travel by air and ground comes to a standstill. Sustained winds during these events are normally 20 to 35 knots with higher gusts likely. Visibilities will be reduced to zero or near zero for much of the event. Temperatures at lower elevations still hover above 105 F (42 C) during these events.
Heat, another feature in the summer that affects aircrews and aircraft is the heat. Of all the natural hazards in the United States, heat is the number one non-severe weather-related killer. Excessive temperatures can lead to many heat injuries such as heat cramps, heat exhaustion and heatstroke, which are listed in order of increasing severity. It is imperative that you recognize the symptoms of heat injury.
Heavy sweating and painful muscle spasms in the legs and stomach are signs of heat cramps. To alleviate these painful spasms, apply firm pressure on cramping muscles and massage to relieve spasms. Also take sips of water.
With heat exhaustion, you might experience heavy sweating; weakness; cold, pale and clammy skin; and a thready pulse, along with fainting and vomiting. To lessen the effects, get out of the sun and into an air-conditioned or fanned room. Lie down and loosen clothing; apply cool, wet cloths; and take sips of water.
Heat or sunstroke is the most critical of all heat injuries. Seek emergency help immediately. Signs of heat stroke include high body temperature (106 F or higher); hot, dry skin; rapid or strong pulse; and, possibly, unconsciousness. Move victims to a cooler environment, remove their clothing and give them a cold bath or use cold sponges or towels. Do not give fluids.
Preventive measures will help Soldier avoid a heat-related incident. Drink plenty of water to stay hydrated. Alcohol and caffeine will only serve to dehydrate the body. Dress in lightweight, light-colored clothing. If at all feasible, avoid sun exposure during the hottest time of the day (10 a.m. to 2 p.m.) and stay indoors as much as possible. Always stay alert to possible heat injuries.
Density altitude is defined as the pressure altitude corrected for temperature deviations from the standard atmosphere. Changes in air density are caused by variations in atmospheric pressure, temperature and humidity. The lift of an aircraft wing or blade is affected by the speed of the air around it and the density of the air through which it moves. Lift will be increased by cold, dense air. An increase in both temperature and humidity causes a reduction in air density. Thus, in hot and humid conditions, the DA at a particular location might be significantly higher than the geometric altitude.
Too often, pilots associate DA only with high-elevation airports. Certainly, the effects of DA on aircraft performance are increasingly dramatic in operations from such airports, especially when the temperature is also hot. However, it is important to remember that DA also has a negative effect on performance at low-elevation airports when the temperature goes above the standard air value of 15 C at sea level. Remember also that the standard air temperature value decreases with altitude.
There are many spring and summer hazards. Taking preventive measures and being fully aware of operational weather is vital to mitigating many of these hazards. The first step in preparedness is establishing a severe weather action plan for home, work, school and outdoors. Always respect the weather.
Editor's note: This article was reviewed and approved by Air Force Weather.
Knowledge magazine is always looking for contributing authors to provide ground, aviation, driving and off-duty safety articles. Don't let the fact that you've never written an article for publication scare you. Our editors promise to make you look good. By sharing your knowledge, you can make a valuable contribution to those who need your information to do their jobs safely. Your article might just save another Soldier's life. To learn more, visit https://safety.army.mil/MEDIA/Knowledge/TellYourStory.aspx.