Why the hail, and why so big?

Posted at 5:59 PM, Aug 08, 2018
and last updated 2019-04-26 16:28:41-04

FOUNTAIN – So, I and the entire weather staff have been getting numerous questions on hail of late…so perhaps a brief explainer will help. You’ll still have to deal with living through it, but perhaps an explanation, can help us understand it better.

Hail is, in fact, a frequent thing, here in Colorado. It is frequent…but generally small (pea-size) over the mountains, and frequent but usually larger…the further you are…into the Plains.

Before even bothering to explain size, it helps to explain first…how storms form, because understanding storm formation reduces the need to explain hail. Storms form for several reasons. A cold front, digging the surface air up and lifting it as a fluid, can set them off. Wind, pushing air up a mountain slope, mechanically forms storms (if conditions are right…heat & moisture…in attainable distance below the “condensation” and the “freezing levels”.)

In any event, let us assume that the storm forms, regardless of which way, above. Cells develop their own vertical circulation. There is the updraft in the middle and front, and the downdraft on all sides. It is a giant “vacuum”, sucking in warm, moist air, elevating it quickly, and then spewing it out the back and sides.

This mechanism, also carries much of the raindrops within the storm, up the center, or “core.” They rise rapidly, hitting the freezing layer (which can change in elevation, daily, adding difficulty to forecasting these.) Once they freeze, they descend downward, usually out the back of the storm. But, they often get caught up, repeatedly, in this “core”, and while at the bottom, raindrops hit the new hailstone, adding a layer of water, which then forms a new layer of ice, once driven to the top of the core. Only to fall again, and again…only and until the weight of the stone (gravity), overcomes the strength of the updraft (core).

A reason why places like Fountain get large-r hail sometimes, is because if the storms form over Pikes Peak, and drift southeast along the peaks, they have a little further to travel over peaks, by going over Cheyenne Mountain. And then, the storm cell hits a sudden major drop in elevation, or better put, a sudden major increase in available volume (air), and they experience sudden, one-time, growth, as they hit Fountain!

Now, this is only a problem, in Fountain’s case, if they form near Pikes Peak and winds take them south, rather than any other direction. But when that happens, that sudden increase in air volume has a dramatic impact on people’s car windshields!