[Geography Notes] on Hail Meteorology Pdf for Exam

Hail is a kind of solid precipitation, different from ice pellets. It includes balls or irregular lumps of ice, each of which is known as a hailstone. Ice pellets generally fall in cold weather whereas the growth of hail is immensely constrained at cold surface temperature. In contrast to ice pellets, hailstone usually measures between 5 mm (0.2 in) and 15 cm (6 in) in diameter. Hailstone is most commonly found in mid-latitudes and usually lasts around 15 minutes. They generally occur in mid – to -late afternoon. 

Hail is extremely destructive to crops and buildings if large enough, or it may be even dangerous to animals exposed to it.

Hailstorm Definition  

Any thunderstorm through which hail is produced and reaches the ground is known as a hailstorm. Hail has a diameter of 5 mm (0.20 in) or more and can grow to 15 cm (6 in) and weighs more than 0.5 kilograms.

In contrast to ice pellets, a hailstone is stratified and can be irregular and clustered together. Hail consists of transparent ice and alternating layers of transparent and translucent ice at least 1 mm ( 0.039 in) thick, which are laid down upon the hailstone as it travels through the clouds, held off above by air with strong upward motion until its weight exceeds the updraft and falls to the ground. 

The diameter of hail is generally varied, in the United States, the damaged hail, on average, is observed between 2.5 cm (1 in) and golf ball-sized  ( 1.75 in). Stones larger than (0.80 in) are considered to be large enough to cause damage.

Hailstone Formation

Hailstone formation or hail formation occurs when the rain droplets are carried upward through thunderstorm updraft into immensely cold areas and freezes. Hailstones then further grow by hitting liquid water droplets that freeze into the surface of the hailstone. If the water freezes speedily when hitting the hailstone, cloudy ice will form as the air bubbles will be confined in the newly formed ice. However, if the water evaporates slowly, the air droplets will escape and the newly formed ice will be clear. The hails fall when thunderstorm updraft can no longer support thunderstorms weight, which can come about if the stone becomes large enough or the updraft weakens.

Hailstone Meteorology Size

The hailstone size can be best described by measuring the diameter using a ruler. In the absence of a ruler, the hailstone size can be best estimated by comparing its size to that of known objects, known as coins. Comparing the hailstone size using the objects such as eggs, peas, marbles is imprecise due to the varied dimensions. The UK organization, TORRO also measures for both hailstone and hailstorms.

When observing the hail at an airport, METAR code is used within the surface observation which is related to the size of the hailstone. The GR within the metric code is used to represent the larger hail, of a diameter of the latest 0.25 inches (6.4 mm).

The terminal velocity of hail or the speed at which hailstone is falling when striking the ground changes. It is estimated that a hailstone of 1 cm (0.39 inches) in diameter falls at a rate of 9 meters per second (20 mph) while the stone size of 8 cm (3.1 inches) in diameter falls at a rate of 48 meters per e camph. The speed of hailstone cannot be determined accurately as they are not in spheres. 

Did You Know?

• Hailstone can fall at a speed between 9 mph (14 km/hr) and 110 mph (17 km/hr).

• The larger hailstones are faster to fall.

• The hailstorm most commonly occurs in one of the areas of the United States known as the hail alley.

• Hailstorms are formed when thunderstorms carry rain droplets up into the extremely cold areas of the Earth’s atmosphere.

• Approximately 200 to 600 nomads seem to have died of injuries. The haistone of thel size of a cricket ball occurred around the 9th century in Roopkund, Uttarakhand, and India.