Summertime Is Peak Flash Flood Season Across Nation, Including Here In Vermont

Flash flooding during a torrential downpour in 
Jericho, Vermont, July 4, 2013. Summer time 
brings the highest risk of flash floods. Seems 
there's a flash flood daily in the summer somewhere
in the United States. Almost every summer brings
at least one instance of flash flooding
somewhere in Vermont. 

 Flash floods can occur any time of year, pretty much anywhere. But summertime is when we can expect them most often, and often, they're the most deadly.  

From now on into September at least, we'll see flash flood trouble spots almost daily somewhere in the United States.

As of this morning, parts of central Oklahoma are drenched and in some cases flooded. Pockets of heavy rain in the Mid-Atlantic States and parts of Washington State could see some flash flooding today.

A tropical system which might become Tropical Storm Alex, is expected to bring torrential rain tomorrow and over the weekend to South Florida, so flash flooding is a good bet there. On and on it goes. 

Here in Vermont, though rain is in the forecast for Friday, we will NOT see enough rain then to cause flooding. However, some of our worst flash flood events have occurred in June. Think June, 1973, and June, 1998 as examples. Of course, the risk continues on through the summer. 

Several reasons conspire to increase the risk of flash flooding in the summer. It can get hot and humid in the summer, duh!! 

That kind of air can hold a TON of water.  Thunderstorms forming in this humid air can dump tremendous amounts of water in a short time. 

Also, summer time air flow is often sluggish. We sometimes don't have enough wind to push a thunderstorm along very fast. So it sits in one area and pours its water on one spot. Or, thunderstorms line up like boxcars on a railroad track and go over the same spot over and over again, so a narrow band of real estate ends up suffering from a damaging flash floods.

Flash floods are often localized like that. I've seen instances in which one town is badly flooded while the pavement is still dry in a town less than 10 miles away. 

Tropical storms and hurricanes are obviously another way to see a flash flood.  They'll often hold onto a lot of moisture and cause damaging floods way inland. 

Aftermath of flash flooding, Barre, Vermont, May, 2011.

Or, the remnants of an old tropical storm can interact with another weather system to unleash a catastrophic flash flood a thousand or more miles away from where the storm came ashore. We saw that last year when Hurricane Ida hit Louisiana, and a few days later, its remains unleashed a terrible flood on the New York City area.

An even more extreme example of this came in 1997. Moisture from offshore Tropical Storm Claudette interacted with a stalled cold front over the northern Green Mountains to produce the devastating flash flood of July 15, 1997 in and around Montgomery, Vermont. 

Similarly, in 1995, a forgettable tropical storm named Dean hit the Texas coast on July 30.  Its remnants interacted with another stalled weather front in Vermont to produce destructive flash flooding in northern parts of the state on August 4-6 that year, especially in the Lamoille River Valley.

Climate change ups the ante with flash floods.  It's causing the air to become generally warmer and, especially in the eastern United States, wetter. This creates more potential for torrential downpours ad floods.

Though drought periods are increasing somewhat, overall rainfall has increased here in Vermont in recent decades.  That helps to explain why flash floods seem to have become more common in the Green Mountain State.

We've seen at least localized flash flooding in Vermont almost every summer for over two decades now.  Already, we've seen a bit of flash flooding around Proctor, Florence and West Rutland in mid-May. I fully expect to see addition flooding of this type in Vermont as we go through the summer. 

As the name implies, you don't know you're going to be hit by a flash flood until just before it happens. During periods of stormy summer weather, definitely check in with the National Weather Service for flash flood watches, warnings and statements. 

If you find yourself under a flash flood warning, move quickly to higher ground and whatever you do, don't drive over a flooded road. You don't know how deep the water is, or whether the road is even still there. Most flood deaths are in vehicles. 

We love summer rain storms. We need them.  Like every good thing in life, too much turns into a bad thing.