Summer Doldrums Contribute to Local Flash Floods

A flash flood in Jericho, Vermont in July, 2013.  

Flash flood warnings have sprouted in various sections of the country over the past few days.

We're in the peak of the season of slow moving thunderstorms. Those storms can drop major rains in a short time in local areas.

Yesterday in San Bernardino, California, flash floods and debris flows caused by slow storms caused by seasonal monsoons killed one person and stranded many others.

Flash flood warnings popped up occasionally in small areas of Pennsylvania and New York Sunday under some storms. And this morning, far northern New Hampshire and a piece of western Maine is under a flash flood warning as slow moving downpours hang out in that region.

In the height of summer, upper level winds are often slack, much lighter than they are at other times of the year. When thunderstorms form, the lame high level winds mean there's not much to push them along, so they sit over one area, dumping their rain until creeks and streams become torrents.

In the grand scheme of things, thunderstorms usually don't cover a large area. So very often in these situations, one town might have huge trouble with raging waters, while the next town three miles up the road stays totally dry.

I noticed here in Vermont that radar estimates indicate at least an inch and a half of rain fell in parts of the northeastern parts of the state, while less than a tenth of an inch had fallen in places like Burlington in western Vermont.

In the Northeast, upper level winds will pick up a little today and tomorrow ahead of a cold front.  While there will be more thunderstorms, at least they won't stay over one area too long, minimizing the flood threat.

Not so in the deserts of California, Nevada and Arizona, and on up into Utah and southern Idaho. In that region, it doesn't take a huge amount of rain to set off some flooding.

More slow moving, torrential storms are likely in that region today, meaning more flash flooding is a good bet.

On the bright side, some areas of southern California and Arizona have seen enough rain to put a teeny, tiny dent in the ongoing, severe drought out there.