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Hail
Showery precipitation in the form of irregular pellets or balls of ice more than 5 mm in diameter, falling from a cumulonimbus cloud.
Hail Contamination
A limitation in NEXRAD rainfall estimates whereby abnormally high reflectivities associated with hail are converted to rainfall rates and rainfall accumulations. These high reflectivity values are mistaken by the radar for extremely heavy rain, thus "contaminating" (inflating) its estimation of how much rain has fallen over the affected area.
Hail Index
An indication of whether the thunderstorm structure of each storm identified is conducive to the production of hail.
Hail Size
Typically refers to the diameter of the hailstones. Warnings and reports may report hail size through comparisons with real-world objects that correspond to certain diameters:

DescriptionDiameter (inches)
Pea0.25
Marble or Mothball0.50
Penny or Dime0.75
Nickel0.88
Quarter1.00
Half Dollar1.25
Walnut or Ping Pong Ball1.50
Golfball1.75
Hen's Egg2.00
Tennis Ball2.50
Baseball2.75
Tea Cup3.00
Grapefruit4.00
Softball4.50
Hail Spike
An area of reflectivity extending away from the radar immediately behind a thunderstorm with extremely large hail. In an area of large hail, radiation from the radar can bounce from hailstone to hailstone before being reflected back to the radar. The time delay between the backscattered radiation from the storm and the bounced and scattered radiation from the large hail causes the reflectivity from the hail to appear to come from a farther range than the actual storm.
Probability of Hail
(Abbrev. POH) - a product from the NEXRAD hail detection algorithm that estimates the likelihood that hail is present in a storm.
Small Hail
Technically used to refer to snow pellets or graupel.

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     Page last Modified: 25 June, 2009 1:01 PM