How large can hail get?
The largest hailstone recovered in the U.S. fell in Aurora, NE on June 22, 2003 with a diameter of 7 inches and a circumference of 18.75 inches. Since its weight could not be determined, the hailstone that fell on Coffeyville KS in 1970 remains the largest on record at 5.7 inches and 1.67 pounds, with a circumference of 17.5 inches.
Why does the sky look green during some hailstorms?
Scientists don't agree on why the sky may rarely appear green during severe weather, although there is plenty of annecdotal evidence that it can, and that hail may be nearby. One theory is that large amounts of water and ice in a severe thunderstorm will scatter green light during the strong updrafts that occur in severe storms. Some people report the sky seems "brighter".
Does a hailstorm mean there could also be a tornado?
Not always, but possibly. Since large hail often appears near the area within a thunderstorm where tornadoes are most likely to form, you should assume a tornado could be nearby and seek appropriate shelter.
Why is 3/4" the criteria for hail?
The 3/4" size limit for hail is based on a 1952 study of the "smallest size of hailstones that cause significant damage at airplane speeds between 200 and 300 mph." Though this was based on DC-3 type aircraft, hail remains a significant hazard to aviation.
Is hail dangerous to aircraft?
Yes. On April 4, 1977, a Southern Airways DC-9 crashed in New Hope, GA. Both engines of the plane ingested hail and lost thrust. The plane crashed onto the road and burst into flames. Two of the four crew members and 60 of the 81 passengers were killed; eight others on the ground were also killed.
What is hail?
Hail is precipitation that is formed when updrafts in thunderstorms carry raindrops upward into extremely cold areas of the atmosphere and freezes into ice. Hailstones grow by colliding with supercooled water drops. Thunderstorms that have a strong updraft keep lifting the hailstones up to the top of the cloud so they continue to grow. The hail falls when the thunderstorm's updraft can no longer support the weight of the ice. The stronger the updraft, the larger the hailstone can grow.
Can we predict hail?
Hail can be predicted using radar. On Doppler radar, hail generally sends a return signal that looks like extremely heavy rainfall. We are also studying the use of polarimetric radar (radar that sends horizontal and vertical pulses) because it can detect actual ice, and determine the location of severe hail.
How does hail fall?
My neighbors on both sides had hail damage to their roofs, and I did not. How is this possible? NSSL works to predict hail, we do not study hail damage from an engineering perspective. However, there are a number of reasons why your roof did not show damage. It is possible that your roof had better shingles, or newer shingles. The direction of your main roofline, the distance between the houses, whether or not the wind was driving the hail – all these can make a difference in the amount of damage you can receive.
Is there a way to find out the peak hail season for my area?
By using NSSL's Severe Thunderstorm Climatology graphs you can see the annual cycle of the probability of any type of severe weather occurring within 25 miles at any point you select.
Where can I find data on hailstorms?
The National Climatic Data Center is the official archive for all U.S. weather events. Click on Weather/Climate Events, Data and Products, then the U.S. Storm Events Database.
What is the difference between hail, sleet, and snow?
The type of precipitation is defined by the process by which it was formed. Hail only comes from thunderstorms because it is the thunderstorm updraft that keeps the pieces of ice from falling. Drops of supercooled water hit the ice and freeze, causing it to grow. Sleet forms from raindrops that freeze on their way down through a cloud. There is no thunderstorm updraft involved in the formation of sleet or snow.
How fast does hail fall?
How hail falls is dependent on what is going on inside the thunderstorm. Hail falls when it becomes heavy enough to overcome the strength of the updraft and is pulled by gravity towards the earth. Hailstones bump into other raindrops and other hailstones inside the thunderstorm. This bumping slows down their fall. Drag and friction are also factors. We really only have estimates about the speed hails falls. The fall speed equation (1.4*D0.8) where D is the diameter in mm, assuming a perfect sphere at sea level and a "typical" hail density of about .92g/cc, says that a 5cm diameter hailstone can fall at a speed of 32 m/s or 71mph! A hailstone is not likely to reach terminal velocity due to friction, collisions with other hailstones or raindrops, wind, the viscosity of the wind, and melting. Also, the formula to calculate terminal velocity is based on the assumption that you are dealing with a perfect sphere. Hail is generally not a perfect sphere.
Do thunderstorms throw hail like a popcorn popper?
There have been reports of hail being thrown from a thunderstorm, but it is rare and it usually melts before it hits the ground. Most hail falls in the main part of the thunderstorm, and either straight down or at a bit of an angle if it gets blown by the wind.
Are "normal" thunderstorms able to produce golf ball size hail or larger?
Yes, many non-supercell storms produce golf ball size hail.
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