‘Out of Nowhere:’ strong winds drop out of summer storms in an instant

Several small storms this week have produced, what we often say, is the ‘worst weather a person might see all year long’ in North Alabama.  So what gives?  We end up with things like this from New Hope on Tuesday night:

And also from Tuesday night, this happened near Albertville.

Whitney asks a great question: what happened?!

So how do they work?

Summer storms are more simple than the severe storms of the other seasons: updrafts and downdrafts.  Hot, humid air rises (quickly) creating the storm, but eventually that air cools, condenses out water vapor, and gets too heavy for the updraft to hold.  That’s when it crashes to the ground in what we call a ‘downburst.’  Those downbursts can fall to the ground at up to 100 miles per hour, and when they hit the ground all of that energy spreads out on the ground as damaging winds.

Image: National Weather Service

Here’s an example of what it looks like on radar looking at the storm’s vertical characteristics.  Why can’t see see this in ‘real time?’  It’s simple.  Radar gives us a series of snapshots that we have to piece together.  Once this ‘collapse’ occurs, the wind has already happened and it’s too late to warn you about it.

Worst all year you say?  Yep!  Some of the nastiest storms of the year happen in the summer season, but they are not always ‘severe’ like the powerful, destructive storms of Spring and Fall (the ones that bring the extreme winds and tornadoes).  Most of us never have to deal with a tornado; only 1% of Alabama’s land area was impacted by a tornado on April 27, 2011 (the largest, deadliest tornado outbreak in a generation).

The Storm Prediction Center’s severe weather climatology shows how the risk of severe storms (mainly from wind) actually increases from May through June and July over a big part of the Southeast:

Summertime storms work differently than those driven by dynamic jet-stream-driven storm systems, and it can be very, very difficult to ‘see‘ what they’re doing on radar because they aren’t spinning or causing long-term strong winds that are more easily tracked in the Spring/Fall storms.

A storm does not have to be ‘severe’ to bring strong winds that can break branches on trees, heavy rain that can cause flash flooding, and dangerous (deadly) cloud-to-ground lightning.

Sometimes these storms congeal into a large MCS: a mesoscale convective system.  Those big masses of thunderstorms can do a lot of damage while producing only downbursts.  One particular MCS from last summer stands out as a prime example of how nasty these things can be: the derecho of June 28, 2018.

Here’s the deal.  It does not matter if the wind is swirling in a funnel with a Tornado Warning or if it’s blowing along the ground in a straight line; wind gusts that high are dangerous.

Anytime there’s a storm in the area, take it seriously: especially if there is a Severe Thunderstorm Warning!

You can get free lightning alerts, warnings, and notifications about storms in the general area with Live Alert 19!

Looking for the rest of the forecast? It’s always online at WHNT.com/Weather and in the “Daily Forecast” section on Live Alert 19!

-Jason
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