Thursday, May 15, 2014

Stuck Weather Pattern Causes Trouble, AGAIN!

One interesting facet in the study of how global warming is affecting day to day weather patterns is the idea that it might encourage "stuck'" weather systems.  
From@MarkBiddinger via Twitter,
 a tornado in Ohio Wednesday,
caused in part by a stalled weather
front in the eastern United States.  

That's what might be behind this past winter, when a stuck ridge of high pressure kept rain away from California, intensifying a terrible drought that has brought on big early season wild fires. 

The stuck pattern contributed to the consistent winter and early spring cold in the Midwest and Northeast, and the destructive parade of storms that trashed Britain over the winter.

The theory is, the jet stream which propels weather systems generally from west to east across the northern hemisphere, thrives on the difference between the very cold Arctic and the hot tropics.

Since the Arctic is warming faster than the tropics, there's not as much of a north to south temperature contrast. This would slow the jet stream, causing it to meander and get stuck in a pattern where the same kind of weather hits the same location for a long period of time.

The jet stream has always gotten "stuck" from time to time. It just appears to be happening much more frequently nowadays. And it seems to be stuck again today, and that could spell more trouble.

A caveat: While human caused global warming is a proven fact, the evidence that it causes stuck weather patterns is strong, but not proven.

And the stalled weather front and renewed flooding in the eastern United States that I'm about to talk about might or might not have to do with climate change.  One storm does little to prove or disprove  climate change.

In any event, a cold front, the type of system that usually moves from the Midwest to off the East Coast within two or three days, has been inching its way across the Midwest and Ohio Valley for days now.

It has caused three consecutive days of tornadoes in Ohio.

Now the front is finally getting close to the East Coast, and it is getting even slower. That has given the front, which is oriented north to south, to draw lots of tropical moisture from around Cuba up its eastern flank.

That's not too unusual. Cold fronts sometimes collect plenty of moisture, which leads to downpours. No big deal, really. Since cold fronts move right along, the downpours only last a few hours in one particular spot, so nothing too bad comes of it.

This time, the front is so slow the heavy rain will last a long time in any given spot. There's flood watches in a long stripe from the Florida panhandle all the way north to western New York because of this fact.

Many of these areas saw heavy rain earlier this month from, yes, yet another stalled weather front. That stuck storm caused damaging floods from Florida to the New York City metro area.

Even as it is stuck, the nature of this front is changing, so the threat of tornadoes and severe thunderstorms is diminishing, especially in the Northeast. But the flood threat is growing.

For my Vermont area readers, since the greatest concentration of them are up here, where I also live, I'm not yet too concerned the slow front will cause much flooding here.

That other stalled front earlier this month didn't drop that much rain on the Green Mountain State, so it's not that wet to begin with. Some heavy rain can soak into the ground.

This next super slow front will probably drop one to three inches of rain in Vermont when it gets here Friday afternoon and Saturday, less than in other parts of the East. So there might be minor flooding, but no cataclysm.

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