Hail: Understanding The Threat

Hail: Understanding The Threat
Weather Talk

POSTED: Thursday, February 24, 2011 - 2:37pm

UPDATED: Friday, February 25, 2011 - 11:14am

(STORMTRACKER33) -- Hail is frozen precipitation. Basically hail is frozen water that leaves a cloud as ice, and lands on the ground still in an ice state. Hail stones can be very small (gravel sized) to larger than a softball. The largest hailstone ever recorded was larger than 5.5" across and weighed 1.67 pounds. 

How Hail Forms

Cross section of a thunderstorm:

Courtesy of NWS Columbia, SC

1. Inside a thunderstorm are strong updrafts of warm air and down drafts of cold air. 

2. If a condensed rain droplet is falling through the cloud and it gets caught in the updraft it can be carried back up into the cloud above the freezing level. Temperatures are below 32 degrees above the freezing level. When the droplet is carried this high in the cloud it freezes.

3. The now frozen droplet will begin to fall again within the cold down draft. At this point it will do one of two things, thaw as it moves into the warmer air toward the bottom of the cloud and fall out as rain. Or it may get caught in another updraft carrying it back up into the very cold air and re-freeze it. 

4. As our frozen friend goes around and around inside the cloud, it re-freezes and thaws adding layers of ice  to itself until finally it is so heavy it falls out of the cloud to the ground as hail. 

This act of freezing and refreezing within a cloud causes the hail to have a ring-like structure similar to the rings of a tree.


Estimating Hail Size

Pea = 1/4 inch diameter

Marble/mothball = 1/2 inch diameter

Dime/Penny = 3/4 inch diameter - hail penny size or larger is considered severe

Nickel = 7/8 inch

Quarter = 1 inch

Ping-Pong Ball = 1 1/2 inch

Golf Ball = 1 3/4 inches

Tennis Ball = 2 1/2 inches

Baseball = 2 3/4 inches

Tea cup = 3 inches

Grapefruit = 4 inches

Softball = 4 1/2 inches 


Hail Facts/Myths:

1. If a storm produces hail it will also produce a tornado.

FALSE: Hail means a thunderstorm has very strong updrafts and down drafts. Tornado's are also associated with storms that have very strong updrafts and down drafts, and large hail is often observed immediately North of tornado tracks. However the presence of hail does not mean there will always be a tornado as well. There have been many occurrences of hail without tornado's. 

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