Hailstorms
Hail causes more than $1 billion in crop losses annually in the U.S.
Hail also causes significant property damage, primarily to automobiles, aircraft and the roofs, siding and windows of structures.
Hail is most common in the high plains east of the Rockies.
Hail is most common in late Spring and Summer.
Most hailstones are solid and hard, but some are soft and spongy.
Hailstones can be spherical, conical, or irregular in shape.
When a developing thunderstorm rises to levels where the ambient air temp is below -15 C, ice particles begin to form in the storm; some are carried into the anvil in the strong updraft, but others remain near the periphery of the updraft and begin to fall due to gravity.
The falling ice crystals grow by collecting supercooled cloud droplets and are called "graupel" once they grow to sizes of 1-5 mm in diameter.
The largest concentration of graupel surrounds the BWER (Bounded Weak Echo Region, also called the Echo-Free Vault); this "hail embryo" curtain of graupel becomes the initial source of particles to grow into hailstones.
The "hail embryos" that are in the periphery of the updraft, such that there fall velocity is marginally less than the updraft velocity, have the greatest chance of collecting supercooled cloud droplets.
As the growing hailstone moves into the core of the updraft, it will "float" and "spiral" in the updraft, while continuing to grow more rapidly to a large size ... sometimes to exceptional size: grapefruit & softball sizes!
The larger hail is eventually carried aloft and ejected to the northeast side of the storm; a "hail cascade" can occur, flanking the east and northeast sides of the updraft; smaller continuous regions of hail are called "hailstreaks", and a larger hailstreak is called a "hailswath."
Hail dry growth regime: when the surface temp of the hailstone remains colder than 0 C, causing supercooled cloud droplets to freeze on impact, thereby trapping small air bubbles, creating a milky or opaque appearance.
Hail wet growth regime: when so much supercooled water freezes on the stone's surface that the released latent heat raises the surface temp to 0 C; this allows the water to spread out and freeze more slowly, giving a clear appearance. (Hail can contain many alternating rings ... clear & opaque.)