Wednesday, March 11, 2015

The Bright Side To Nation's Winter From Hell: Few Tornadoes, Severe Thunderstorms

A deadly tornado flings debris far and wide
in Moore, Oklahoma in May, 2013. So far in
2015 there have been very few tornadoes in the
U.S., but that could change later this spring.  
Snow deeper than an NBA player is tall in New England. Weeks of brutal subzero cold in the Northeast and Midwest. Destructive snow and ice storms in the Tennessee and Ohio Valleys. Crushing drought in California.  

Yes, it's been a winter to remember in much of the nation, and I'm sure these extremes have caused billions of dollars in damage and economic loss.

But the weather pattern that brought you this nightmare winter had one big upside: It has so far prevented tornadoes and severe thunderstorms from forming.

As the tornado chase organization TVN Weather notes, this is the slowest start to a severe weather season in over a decade. It would have been the slowest on record if not or a few tornadoes in the South in the opening days of January.

Through Monday, there had been 28 preliminary reports of tornadoes in the nation so far this year, all of them pretty damn weak. By now, there is, on average, about 95 such reports, say Bob Henson and Dr. Jeff Masters, blogging about the situation at Weather Underground. 

The number of severe thunderstorm and hail reports is even more sparse in 2015. Henson and Masters say there had been 119 preliminary reports of severe winds nationwide as of Monday, compared to an average of 708 up to that date.

By Monday, there were only two reports all year of hail bigger than one inch in diameter. Usually by now there would have been more than 360 such reports.

So what's going on?

The persistent pattern has featured a flow of air from the northwest flow of air over the northern Plains and down into the eastern part of the nation.

That has prevented any big batches of warm, wet, unstable air from moving north out of the Gulf of Mexico and into the United States. Such influxes of humid air are a key ingredient for severe thunderstorms and and tornadoes.

Since the weather pattern has stopped the hot, wet air from the Gulf of Mexico from invading, we haven't had much in the way of severe thunderstorms and tornadoes.

About now, the tornado and severe thunderstorm season in the United States begins to ramp up toward a peak in late April, May and June. On average, the nation is hit with about 80 tornadoes in March, more than 150 in April, about 275 in May and just under 250 in June.

The immediate outlook over the next couple weeks doesn't call for much in the way of severe weather. There is a minimal chance of some briefly severe storms or a very weak tornado or two in Louisiana tomorrow, but it won't be a big deal.

The weather pattern that gave the Northeast such a tough winter is set to return next week and stay put, probably at least into early April. (Sorry New England, that means more cold air and snow for you.)

With this set up, I don't expect much in the way of tornadoes and severe weather for the next couple of weeks at least.

Nobody really knows if the rest of the tornado season will be busy or quiet. There have been some years with very few tornadoes in March and early April, and then lots of strong, destructive twisters in late April, May and June. So you never know.

The last three years have brought some luck in the tornado department to the United States. The period 2012 through 2014 had the lowest consecutive three year total number of tornadoes of any period since at least 1950, says the Weather Channel. 

However, 2011 brought a spate of many large destructive tornadoes that killed hundreds of Americans, especially in Alabama and Missouri.

We can hope the number of tornadoes and severe storms stays low throughout 2015, but unfortunately, we can't count on that.

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