Are You Tornado Prone?

After last week’s first tornado outbreak of the season produced yet another tornado in the city of Moore, Oklahoma, there has been much speculation as to why Moore seems to have become be a tornado target in recent years.  Some have speculated it could be a subtle feature of geography; a combination of the slope of the land and proximity to urban areas causing natural enhancements to thunderstorm inflow.  However, actual results seem to defy such explanations.  Tornadoes are so isolated and uncommon in any one place that it is very hard to find empirical evidence for such conclusions.  Likely as not, when a particular location seems to be tornado prone, it is just random luck.  The forces within a supercell thunderstorm are strong enough to dwarf any local geographical effects.   Meteorologist John Wheeler

Tornado Absence

 

March is typically one of the peak months for tornadoes in the United States.  Though rare so early in our region, it is common for there to be big outbreaks in March across the Southern Plains or the Southeast.  This year, for just the second time since 1950, there were no tornadoes reported across the country from March 1-15.  The other year was 1969. The cause for this year’s absence of twisters is, of course, the jet stream pattern, which has kept the Great Plains extremely dry this month so far.  And although the Southeast has been rainy, the rains have been general soakers.  The pattern just has not favored the development of tornado-producing supercell thunderstorms.  This should not be taken as a sign that our warm season will be free of tornadoes.  Meteorologist John Wheeler

A good Year for Few Tornadoes

The average annual number of tornadoes reported in the United States is about 1,260.  Fairly good records go back to 1953.  The average has been on the rise in recent years, mostly due to a much more active storm spotting network.  The most number of tornadoes in a year was 1,870 in 2004.  Other very active tornado years were 2008 and 2011 with more than 1,600 each of those years.  But for the last three years, there has been a dearth of tornadoes with fewer than 900 observed tornadoes in 2012, 2013, and so far this year.  In fact, barring an unusual Christmas tornado outbreak, 2014 will go down as having the fewest number of tornadoes on record in the modern era (since 1953).  So far, there have been just 814 tornadoes this year.   Meteorologist John Wheeler

Tornadoes #14 and #15

Friday evening, September 19, a supercell thunderstorm produced a sequence of two tornadoes in northwestern Minnesota.  The first tornado touched down near Northcote and on U.S. 75 and travelled east, crossing U.S. 59 south of Lancaster before lifting and travelling a bit further as a funnel cloud.  There was quite a bit of damage to a number of farm buildings in central Kittson County.  The tornado earned an EF2 rating, indicating peak winds between 111 and 135 mph.  the storm then produced a second tornado which traveled several miles across western Roseau County west of Greenbush.  This storm was earned an EF1 rating, suggesting winds between 86 mph and 110 mph.  Though neither tornado would have been considered a “monster” storm, it was an impressive feat for so late in the storm season.  Despite the late-season tornadoes, 2014 continues to be a relatively benign year for tornadoes in our region.  Those two tornadoes Friday were only the fourteenth and fifteenth tornadoes this year over eastern North Dakota and northwestern Minnesota, and the first since July.    Meteorologist John Wheeler

Light Summer, Tornado-Wise

It has not been a very stormy summer.  Across the whole of the United States, there were just 27 tornadoes during August.  This is the lowest tally since 1963.  This statistic becomes even more impressive when you consider that in the 1960s there was no radar and almost no storm spotting or storm chasing networks to observe tornadoes in rural areas.  Several areas of the United States did experience storms with heavy rainfall during August, but the atmospheric mechanics were just not there for tornadoes.  Year to date, this calendar year has produced the fewest tornadoes nation-wide since 2002.  Over the area of eastern North Dakota and northwestern Minnesota covered by the Grand Forks National Weather Service, there were no tornadoes in August and just 13 so far this year.     Meteorologist John Wheeler

Tornado Capital of the World

Caddo County, just west of Oklahoma City, has been hit by at least 111 tornadoes from 1950 through 2012.  The rest of central Oklahoma is about as unlucky.  Geography is to blame, particularly from mid April through mid June when conditions ideal for tornadoes occur with regular frequency.  The Gulf of Mexico and its warm, humid air is close by to the south.  Just to the west and northwest is Colorado and, in particular, the Colorado Front Range with its peaks to 13,000 feet.  The Front Range acts to strengthen low pressure areas which draw dry air from the west and humidity from the south.  The southerly winds near the ground undercut the dry air blowing in rapidly from the west/northwest which creates rapidly rising air and spin.  The result, more often than any other place in the world, is tornadoes.   Meteorologist John Wheeler

Tornadoes Before TV

Lee Sandlin’s book, “Storm Kings: The Untold Story of America’s First Tornado Chasers,” continues to fill my head with ideas even after I finished reading it a couple of weeks ago.  People caught in the path of a significant tornado today are changed forever.  But at least we have television news and, of course, the Internet for observing these storms and their aftermath.  Imagine a European settler in the 1600s or 1700s (even 1800s) experiencing a tornado without having any idea what it was.  Tornadoes are more common in America than anywhere else in the world and the European immigrants to the New World had nothing to reference.  To these people, a tornado must have seemed to have been a metaphysical event, perhaps evoking deeply a deeply spiritual reaction.      Meteorologist John Wheeler

More or Fewer Tornadoes?

The round of violent tornadoes early this week across the South raises the following question. Is our changing climate affecting tornadoes? The two major forces which create favorable environments for tornadoes are atmospheric instability and wind shear. Global climate change models have always indicated that a warming atmosphere will have more instability but less wind shear, suggesting the two would balance each other out. But global climate models are generalized models and have only suggested how these two elements would change in general. New research suggests that wind shear will decrease overall but conditions of high wind shear may increase particularly on the days of high instability. In other words, we might have fewer tornado days but an increase in the number of occasions with a high concentration of tornadoes. This is actually borne out in recent years as records have been set for the most and also the fewest number of tornadoes in a year. Meteorologist John Wheeler

Orange Tornadoes

Last week on Halloween, 42 tornadoes were reported across the country.  Most of those were confirmed with storm survives over the following days.  That was the most tornadoes reported on October 31 since at least 1950.  That was also the highest daily tornado count in the United States since early July.  

Yet, even with a high number of tornadoes recorded last week, the 2013 season overall has been one of the quietest since good severe weather records started in 1950.  Not only has the tornado season been quiet, but so has the Atlantic hurricane season.  Through October the Accumulated Cyclone Energy (ACE) index was the 4th lowest since 1950 for the Atlantic basin.  

Plus, it will probably be another year without a major hurricane strike on the lower 48 states, continuing the longest such streak since at least the Civil War.

Slow but Deadly

The two EF-5 tornadoes in Moore and El Reno, Oklahoma in recent weeks have definitely put severe weather in the headlines.  Yet, even with those two tragic events, the overall tornado count for the year is actually below average.  Through June 9, the preliminary tornado count in the country stood at 518, far below the average count of 930 tornadoes through that date.  The average is based on the years 2005 through 2012.

The preliminary count of 518 is the fewest tornadoes observed since 2005, even lower then last year when a drought impacted most of the plains and with limited thunderstorm activity, there were in turn fewer tornadoes reported.  These past two years with fewer than average tornadoes comes after some very active tornado seasons.  Both 2008 and 2011 recorded around 1500 tornadoes through early June, with 2008 ending up with over 2000 tornadoes reported for that entire year.