What is a 100 Year Storm

With the recent flooding in Atlanta, Georgia you may have heard reporting calling this an equivalent to 100 year storm. A 100 year storm does not occur every 100 years, instead it is referred to as this because the likelihood of a storm of this magnitude has a 1 in 100 chance of striking each year and your chances any given year are very small.

A 100 year storm refers to rainfall totals that have a one percent chance of occurring in any location in any year. Once encountered this ‘100 year storm’ one day does not decrease chances of a second 100 year storm occurring in the same year or coming years. There is a 1 in 100 chance or 1% chance in each year for a 100 year storm to occur in your location.

The same principals exist for a 100 year flood, or similar principals exist for a 50 year storm with a 2% chance each year of such an event occurring. Other “storm” classifications do exist such as 10 year, 20 year, 30 year, 50 year and 100 year storms.

Localities vary in normal precipitation levels within a 24 hour period of time to classify a significant rain event. Precipitation for a locality such as Atlanta, Georgia for example in May differs from that of what is expected in September. In Atlanta, Georgia for example May rainfall totals are 3.95 inches throughout the month and September rainfall totals are a bit higher at 4.04 rainfall expected for the month. Atlanta’s record rainfall is 5.32 inches in a 24 hour period of time.

One should not fear a 100 year storm, instead one should prepare themselves and their family for what “might” come. A 1% chance is not much to worry about until it happens. Take the recent tragedies of Atlanta, Georgia into account and make a plan for your family if the 100 year storm does strike your location in the coming years. Have a plan of action in place and include all family members including the four-legged kind in your plan. Remain safe and aware.