What happened?

What happened?

Credit: WFAA

Hail on the ground in Dallas, shared from WFAA.com YouNews user "tkk4life."



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Posted on June 14, 2012 at 1:53 PM

Updated Thursday, Jun 14 at 4:47 PM

Here’s the big question people are asking, 'Why all the hail yesterday, and how did it grow so large?'

Well, here’s the answer. Wednesday, we had an outflow boundary (mini-front) draped across the Dallas-Fort Worth area, temperatures in the 90s and high humidity levels. All the ingredients were in place for thunderstorm development.

Once we reached the peak heating of the day, about 5 p.m., one thunderstorm fired up in southeastern Denton and southwestern Collin counties. The storm quickly turned severe and started moving south. In the process, it sparked additional boundaries and additional thunderstorm development.

As the storms grew, they intensified into supercell thunderstorms, which are notorious for producing large hail.

Now, it’s time for a little meteorology class on hail formation:

  • Inside of a thunderstorm are strong updrafts of warm air and downdrafts of cold air
  • The updrafts within thunderstorms push rain high into the cloud where very cold air freezes it
  • Once frozen, it starts to fall, but gets caught in another strong updraft where it gathers more moisture on its way back up making it larger.
  • If the updrafts are strong enough they will continue this process for long periods of time, allowing the hail to accumulate more and more ice.
  • When updrafts are this strong, winds of 100 mph to 120 mph, it becomes possible to suspend the hail stone for long periods of time, sometimes allowing it to build it to incredible sizes
  • Hail develops “spikes” on it when the stone is suspended in the air and starts to collide or bump into other hailstones. This is when they merge into one and fall to the ground with an irregular shape.

So, Wednesday, everything came together for supercell formation, and consequently, large damaging hail. This afternoon, just like Wednesday, we have outflow boundaries (mini-fronts) draped across North Texas. And just like Wednesday, we will not be able to see exactly where they are until about one hour before storms start to develop on them.

Unfortunately, there is no way to predict with certainty these types of events. We do know the atmosphere is primed for isolated (20%) thunderstorm development, but right now, it’s a wait-and-see game as to where they’ll fire up. The best time will be during the peak heating of the day, 4 p.m. to 8 p.m. Stay tuned!