Summertime Storms and Their Surprises

Shelf Cloud

Shelf Cloud

Summer storms are an enigma – a mystery when it comes to knowing exactly when and where one will develop and how long it will maintain its intensity. That is why we occasionally get storms like the ones on Thursday evening that literally give you the worst weather you see all year. No watches, no warnings, just hard rain, hail, and high winds – that’s what these things do. Folks in Lawrence County remember this very well from last year’s macroburst that produced 115 MPH winds without so much as a severe thunderstorm warning in place.

The rain and hail are much easier to track and forecast using radar. That’s what radar primarily does: looks at precipitation intensity. Doppler radar allows us to see the direction and speed that those rain drops and hail stones are moving relative to the radar. It’s hard (if not almost impossible) to see the full scope of vertical motion inside a thunderstorm, and that’s why these microbursts like the one that caused damage in the East Limestone area Thursday happen with little or no advance warning.

This time lapse from WHNT News 19’s Jack’s Camera Network should help describe how those vertical motions come into play:

See how those towering cumulonimbus clouds explode upward then seem to collapse? It’s simple elementary or junior high physics – “what goes up must come down.”

In the Spring, severe storms are usually a result of instability and wind shear. In the summertime, a severe storm is usually the result of high instability and little or no shear at all! How can that be?

Think of it this way – a storm that isn’t being pushed along into areas where there is untapped heat and humidity (fuel/instability) cannot survive. It’s got to have a constant fuel source to keep the updraft going. If it runs out of fuel, that updraft can no longer hold up all of the cold, dense, rain-cooled air that it caused in the cloud…so it drops to the ground and spreads out in all directions. The picture below shows how this cold, moist air falls from the storm and impacts the ground:

Microburst - NOAA

Microburst – NOAA

This is the reason I’ve been saying all week that a low percentage chance of rain does NOT mean light rain – it’s a low-end chance of HEAVY thunderstorms…and this is always a possibility.

The Bottom Line:

So what can you do to guard against these sneaky storms? Always assume that when a heavy storm is coming at you in the summer months that the wind could get very strong very quickly. Secure patio furniture, grills, garbage cans, and other loose outdoor objects. If you’re at the swimming pool, head for a building or a car (you shouldn’t be there anyway if there’s lightning in the area).

This kind of wind usually knocks down trees and power lines, and it can be rough on sheds, barns, and other structures like that. Avoid taking shelter in a place that isn’t well-built or that could be hit by a falling tree.

These strong summertime storms are nothing new for those of us who have lived here our entire lives, but I understand that not everyone has that kind of experience! We’ll always be here for you in these situations, so be sure you’re following on social media and checking the blog for updates.

One more time, TWITTER is the preferred method of communicating weather information. Facebook has tinkered with algorithms so much that only 30-50% of the people who are a part of my page actually get to see the information I post. Use the hashtag #valleywx when reporting damage, pictures, or asking questions, and I’ll be sure to see it. Google Plus is becoming my second favorite network, but I default to Twitter since there are so many more users. If you’re on G+, let’s chat there too!

Not sure about this Twitter thing? E-mail me at and I’d be more than happy to help you set it up and get an understanding about how to use it.

Connect with me!
Google+: Jason Simpson
Facebook: Jason Simpson’s Fan Page
Twitter: @simpsonwhnt