Saturday, August 13, 2016

Terrible Floods In Louisiana Now, And New Ones Coming, Hint At Climate Change

Flood chaos in Louisiana Friday, from television
station WBRZ  
Boy, this is a month of flooding in the Grand Ole USA, with Louisiana the latest big victim. 

Recently, we've seen some nasty monsoon flooding in the Desert Southwest, and other bad floods yesterday in parts of Wisconsin and Minnesota.

It got much worse Friday, with an epic flood ongoing in  Louisiana as thunderstorms and torrential rains have pretty much stalled over the area since Thursday night.

The Louisiana floods are epic, and joining a lengthening list of off the charts floods we've had in different parts of the nation over the past year. (Think South Carolina last October, Texas in the winter, West Virginia in June, Maryland a couple weeks back.)

The extreme misery in Louisiana is continuing today, and spreading into the western part of that state, and into east Texas, and eventually Arkansas.

A moisture plume eminating from this mess  -- an atmospheric river - is extending northeastward, prompting flash flood watches in a long stripe from Missouri to Vermont.

(Further down in this post, I'll have a specific Vermont-area update for my fellow Green Mountain Boys and Girls)

The Louisiana floods have killed at least two, but I'm sure the death toll will rise, unfortunately. Many homes that never before came close to flooding are inundated. There have been hundreds of water rescues.

In Livingston Parish, Louisiana, 911 dispatchers managed zillions of flood-related calls even as flood waters surged into the 911 dispatch center.' No fewer than 3,000 homes were flooded in Livingston Parish alone.

Some people were evacuated to two churches, but had to be evacuated again when the churches flooded.

A few areas received two FEET of rain, and some of those areas can expect up to a foot more today.

Even when the rain stops, rivers will keep rising. Many of them in Louisiana are going to have record high crests.

Precipitable water in the air,  a measure of how efficiently showers and storms can drop rainfall, was near record highs even for normally wet Louisiana. The stalled, semi tropical system overhead used this excess water in the air to deadly effciency.

The higher the precipitable water is in a given spot, the heavier the rain will fall if a shower or storm moves over that area.
One of many water rescues in Louisiana Friday.  

That the nearby Gulf of Mexico has record high water temperatures doesn't help, since the higher the water temperature, the more efficient the evaporation is into the air, and that means more water feeding into the sluggish storm.

As I've noted in the past, the number of extreme precipitation events is increasing in much of the world, including the majority of the United States.

With every new flood event I offer this disclaimer and it's appropriate here: While I can't conclusively blame  Louisiana floods - and the potential floods to follow soon elsewhere - on global warming, these events are consistent with what scientists say is happening.

As the world warms, these events will probably only get worse.

On top of all that, more and more of the landscape is getting paved over in many areas, so water can't soak in. That means less water can soak into the ground during storms, so it runs off into creeks, rivers, roads, houses and businesses instead.

Right now, most of the eastern United States has high levels of precipitable water in the atmosphere. As heat waves go, this one in the U.S. isn't that extreme as far as actual temperatures. But the extraordinarly high humidity covering such a wide area poses the potential for trouble.

Even in drought-stricken areas of the Northeast, this high humidity now in place can cause thunderstorms to unleash incredible amounts of rain. There's the risk that lines of these storms can repeatedly go over the same area, causing flash floods even in formerly dry areas.

One such storm unloaded four inches of rain on a few towns near the Connecticut, Rhode Island and Massachusetts border on Friday.

Another similar storm inundated dozens of cars and RV's at the Illinois State Fair Friday.

A slow moving weather front interacting with Gulf of Mexico wet air and all that super humid air in place will continue the risk of flooding in various places over the next week in the mid-Mississippi Valley, Ohio and maybe Tennessee Valley and parts of the Northeast.

For many, this isn't going away anytime soon.


The nearly stalled weather front that I mentioned above sagged southward into Vermont Friday, creating some relief from the heat in the northern parts of the state, and triggered some much needed rain.

Bonus: Nobody got excessively heavy rain, so it was all good.

However, the front is still around, and has become more active today, so the risk of flash flooding in parts of the region is real today into Sunday. There is a flash flood watch in effect for the northern two thirds of Vermont and much of northern New York into Sunday evening.

That semi-stalled front is drifting back north, and we will be in the thick of the humid air again today and tonight. Most of Vermont already was in the soup early Saturday morning.

Given the previous dry conditions, not everybody will get flooded in Vermont today - this is no Hurricane Irene - but local areas might get some dangerous flash flooding..

Here's why: Remember that high level of precipitable water I mentioned in the above national summary?  It's here now in Vermont, too. So any showers and storms that get going will be efficient rain makers.

So the usual heavy rain in thunderstorms today will be doubly torrential. Worse, there's the potential for training: That's when a narrow band of thunderstorms follows one another over one spot, like boxcars on a moving freight train.

Anyone stuck under that narrow band can get many inches of rain, and a flash flood can develop in no time.

That's true even if the ground is dry and dusty right before it rains. If it rains super hard, the water will run off into creeks and small streams, and you get sudden blasts of fast moving water coming off the hills. Very dangerous.

Also, in urban areas, like the middle of Burlington, Rutland, St. Albans, Montpelier, Barre and other towns, streets can very quickly flood in the type of downpour that's possible today and tonight, so be careful there.

The time period with the strongest risk of very heavy rain and flash floods is this afternoon and tonight.

Major rivers in Vermont and eastern New York are running low. The areas that get the flash flood rains will be relatively small, even if the potential for three to six inches of rain is there in those local areas.

The majority of Vermont and eastern New York will only get about one to two inches of rain. The bottom line is the big rivers might rise, but they probably won't flood.

The risk of flooding will decline Sunday afternoon as drier air moves in from the northwest.

Though there may be periods of unsettled weather midweek, at this point, I think we're safe from flooding in Vermont after Sunday. But I still want to watch that midweek stuff: If things stall again, there could conceivably be more trouble.   

Here's a video from Louisiana showing a truck being swept off a road by floodwaters. The driver was later rescued.

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