Radar also tries to determine the maximum diameter of hail falling within a storm cell. The output from this is formatted into inches and placed in the "Max Size" column of the storm attribute table. The size that is estimated by radar is usually overdone and the majority of hail that falls is generally smaller. This is especially true during the summer months. Therefore, National Weather Service radar operators tend to only use the maximum hail size to issue warnings when the probability of severe hail (POSH) is over 50%. Radar hailstone estimates range from <.50 inch to >4.00 inches in diameter by quarter (.25) increments. Warnings and reports may report hail size through comparisons with real-world objects that correspond to certain diameters:
Description Diameter (inches) Pea 0.25 Marble or Mothball 0.50 Penny or Dime 0.75 Nickel 0.88 Quarter 1.00 Half Dollar 1.25 Walnut or Ping Pong Ball 1.50 Golfball 1.75 Hen's Egg 2.00 Tennis Ball 2.50 Baseball 2.75 Tea Cup 3.00 Grapefruit 4.00 Softball 4.50Cells a great distance from the radar site, as well as those which have just developed, may have an unknown, or undetectable, hail size. Check the next scan as to if the unknown size has been resolved, as it may have. If not, try using a different radar site that the storm cell may be closer to. If a maximum hailstone size is not detectable, or unknown, the probabilities of hail and severe hail will not be undetectable as well. A radar cannot detect the maximum size of hail well, or possibly at all, if a thunderstorm is close to the radar site. Beams are unable to extend into the updraft at such a degree from the radar's transmitter. With that said, it is also possible for storms to weaken. Therefore, it is a good practice to check the atmospheric conditions before judging that the "cone of silence" is responsible for the weakening maximum hailstone sizes. Never question the decision of an expert meteorologist to issue or withhold a warning.