If you live in the Great Plains area, you already know it’s hail season. You probably also know that hail coincides with thunderstorms. But how do you know how likely hail will be, and if it does occur, what size hailstones to expect?
Here are some factors to consider:
The higher the elevation, the closer an area is to the cold layers located in the upper atmosphere. What this means is that there is less distance for a hailstone to travel from the cold atmosphere to where it makes contact with the ground – and essentially less time to melt. For this reason, areas like Denver, and Dallas – and those regions located in “hail alley” have the highest number of hail days per year, partly because hail stones don’t need to be as large as they do when falling on lower elevations where there is a greater expanse of warm air, and more time to melt.
WET BULB ZERO LEVEL
While the freezing level of an area determines the depth of the atmosphere that is above freezing, the wet bulb zero level is defined as the freezing level that will result due to evaporative cooling. Evaporative cooling of environmental air happens when air becomes entrained in a thunderstorm, which then lowers the freezing level. This is common effect in the Great Plains area, which further increases the amount of hail days.
CONVECTIVE AVAILABLE POTENTIAL ENERGY (CAPE)
CAPE refers the way in which wind velocities can suspend hailstones within a thunderstorm, where additional ice can be added to them, increasing their size. A high CAPE is associated with high upward vertical velocities within a thunderstorm, and is considered the most important factor in determining hail size.
Precipitable water acts directly against CAPE where higher levels of moisture effectively result in lower CAPE levels. Since the force of gravity pushes down on the liquid water drops, higher precipitable water values lead to smaller hailstones and lower precipitable water levels have the potential to produce large hailstones – especially when significant CAPE is present. One reason hailstones tend to be the largest in the Great Plains is due to low precipitable water levels.
As hail can do considerable damage to your home, it is always best to have a licensed professional roofer check your roof after a severe hail storm.
This article is brought to you by ASAP Roofing, a national roofing company that specializes in hail damage, roofing restoration, and weatherization. ASAP has offices in Denver, Colorado, and Dallas, Texas.