Revisiting a Terrible Tornado

Tornado track across Joplin, MO (May 22, 2011)

Today marks the fifth anniversary of one of the deadliest and most destructive tornadoes in U.S. history.  An EF-5 tornado occurred in the town of Joplin, Missouri on May 22, 2011 which caused an estimated $2.8 billion in damage.  Emergency officials determined it resulted in 158 fatalities, making it the deadliest single tornado to occur anywhere in the United States since modern tornado records began in 1950. 

This unusually intense tornado occurred in a highly populated area.  The EF-5 Joplin tornado was on the ground for approximately six miles, was three-quarters of a mile wide and had sustained winds greater than 200 mph.  The Joplin tornado was part of a larger severe weather outbreak that saw 75 tornadoes from Oklahoma to Wisconsin.  What made 2011 an unusual year was the number of intense tornadoes nationwide.  Scientists determined a total of six EF-5 tornadoes occurred, with another three borderline EF-4/EF-5 tornadoes.  NOAA also reported that the United States had its second highest number of tornadoes (1,691) in 2011, behind only 2004 (1,817). 

Tornadoes were originally measured on the Fujita Scale developed by the late-Dr. Ted Fujita of the University of Chicago.  It was updated or “enhanced” in 2007 and became the “Enhanced Fujita Scale.”  Wind speeds go from 65 – 85 mph in an EF-0 tornado to more than 200 mph in an EF-5 tornado.   The deadliest tornado on record in the U.S. was the “Tri-State Tornado” that occurred on March 18, 1925.  It tracked across three states including Missouri, Illinois and Indiana with a death toll of 695.  Unlike tropical storms and hurricanes, tornadoes are not given names but sometimes get nicknames if they are particularly intense or destructive. 

There have been dramatic changes in the science of meteorology since 1925.  Prior to the advent of weather radar during World War II, there was no way to track thunderstorms over any distance.  Weather satellites didn’t exist until the 1960s.  Since then, meteorologists have used both satellite and radar imagery in conjunction with improved computer forecasting models to issue more accurate weather watches and warnings.  That’s what makes the high fatality rate of the Joplin tornado so tragic.

Although there were a few minutes of advance warning in Joplin, it’s difficult to get large groups of people to safety in such a relatively short period of time.  Some have heard the myth that major cities don’t have tornadoes.  However, there have been many examples to the contrary over the last 20 years with tornadoes in Salt Lake City, Philadelphia, Minneapolis and Los Angeles.  The boroughs of Queens, Brooklyn and the Bronx in New York City even experienced weak tornadoes in 2010!

Fortunately, meteorologists and emergency planners have more and better tools to effectively communicate the latest weather watches and warnings.  Social media has made it so much easier to get the word out to the general public – including people who aren’t near a TV or radio.  Many weather apps also exists for smart phones and tablets that also enable people to stay informed when dangerous weather threatens. 

Weather Quiz

True or False.

A tropical storm has formed before hurricane season begins in the Atlantic Ocean (June 1) in three of the last five years – including 2016.

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Answer to Weather Quiz question from April 29.

B.  A half inch of snow fell in the Nation’s Capital on April 28, 1898 for the latest in the season measurable snow has fallen.  However, snow occurred as late as May 16 (in 1988) in the Nation’s Capital.  Although not enough to measure downtown, a trace of snow was officially observed at National Airport.

Cool, Wet and un-May like

NOAA hints at a potential warm up by late-May

Many Washingtonians will recall that May 2015 was the warmest on record in the Nation’s Capital.  It was also the fifth time in the previous six years that May had been drier than average.  However, temperatures so far this month have been more than four degrees cooler than average.  Also, there has already been more rain at National Airport (4.01”) than is average for all of May (3.99”).

Four days this month have had high temperatures only in the 50s for the first time since May 2005.  That’s more than halfway to the record of seven for most May days below 60 degrees in Washington, D.C.  There hasn’t been any 80-degree warmth so far this month and none is expected until at least next week.  Daily average high temperatures are in the 70s for most of May, so 80-degree warmth is quite common in May.  In fact, 90-degree heat has occurred in Washington, D.C. during 15 of the last 23 May’s according to the National Weather Service.

Since this cooler and wetter than average weather began late last month, people have compared our weather to that of Seattle, Washington.  While Seattle’s reputation for sustained periods of rainy and cool weather is well known, it has actually been significantly warmer and drier than average there this spring.  Ironically, while Seattle averages more days with measureable rain in a given year than Washington, D.C. (152 to 115 days), Washington, D.C. averages more annual rainfall (39.74” to 36.15”), according to NOAA. 

This month’s cool weather and record streak of 15 consecutive days with measureable rain (that continued through May 11) has been inhospitable for outdoor activities.  Although there have been only three dry days so far this month, it’s too early to call this one of the coolest and wettest Mays on record.

As this May’s rainy pattern continues, you will hear more comparisons to the record-setting May of 2003 when rain fell on 24 days.  Overall, Washington, D.C.’s wettest May on record occurred in both 1953 and 1889 when 10.69” of rain fell.  Our coolest May on record occurred twice – most recently in 1907 – when the average temperature (combining daily high and low temperatures) was 59.2 degrees.

A New Hurricane Season

A quiet first day of the hurricane season  (Source: NOAA)

Today is the first day of the hurricane season in the eastern Pacific Ocean.  Hurricane season runs in the tropical east Pacific (north of the equator, west of Mexico and east of Hawaii) from May 15 – November 30.  The last two seasons have had several damaging hurricanes, as well as the strongest observed hurricane in the western Hemisphere – Patricia – that occurred last October. 

Mexico’s national weather organization, the Servicio Meteorológico Nacional, is calling for a near average hurricane season with 17 tropical storms, of which 9 become hurricanes and 4 of those become major hurricanes.  By comparison, an “average” season in the tropical east Pacific includes 15 tropical storms, 8 hurricanes and 4 major hurricanes.  That’s based on the running 30-year average from 1980 to 2010.  A tropical storm features sustained winds of at least 39 mph around the center of circulation.  It becomes a hurricane when sustained winds reach 74 mph.  A hurricane becomes “major” when sustained winds reach at least 111 mph – making it a Category 3 storm on the Saffir-Simpson Scale.

One of the hallmarks of a powerful El Nino event is warmer than average water in the tropical eastern Pacific Ocean.  That helps create more favorable conditions for tropical storm development.  However, there have been active seasons in the eastern Pacific Ocean during non-El Nino seasons too.  Such was the case during the 2014 season that saw 20 tropical storms, 15 hurricanes and 8 major hurricanes.  Although no tropical storms have developed yet in the eastern Pacific in 2016, there has been at least one named storm during the month of May every year since 2011.

Having a moderate to strong El Nino or La Nina doesn’t always correlate to an above or below average hurricane season in the eastern Pacific or Atlantic Ocean.  For example, the 2013 and 2014 hurricane seasons were both quieter than average in the Atlantic Ocean, while the tropical east Pacific had more named storms than average each year.  Although the presence of El Nino or La Nina can influence the tropics, a number of factors play a role in how active the tropics become (e.g. amount of wind shear, sea surface temperatures).  Hurricanes require a lack of wind shear as well as warm sea surface temperatures of at least 80 degrees Fahrenheit to develop.

While the tropical east Pacific has been busier than average since 2013, the tropical Atlantic hasn’t had an active hurricane season since 2012.  However, having fewer storms doesn’t mean you should be any less prepared.  Many significant storms have occurred in quieter than average seasons, such as Andrew in 1992.  Now that hurricane season is underway in the tropical east Pacific, NOAA will watch for any tropical development and will issue its forecast for the 2016 Atlantic hurricane season before it begins on June 1.

A Wild Weather Ride in May 2016

The weather during the first two weeks of May 2016 couldn’t be more different than what Washingtonians experienced during the same period last year.  May 2015 was the warmest May on record and the 5^th drier than average May since 2010.  Meanwhile, this May has featured a continuation of the cooler and wetter than average weather in the Mid-Atlantic Region that began late last month.

Washington, D.C. has broken its all-time record for consecutive days with measurable precipitation.  There has been at least 0.01” of rain every day in the Nation’s Capital for the last 15 days since April 27.  The previous record was 10 consecutive days of measurable rainfall that occurred twice – most recently in July 1938.  Rainfall chances are less today so the streak could end at 15 days.  However, rainfall chances increase again tomorrow and Saturday.

Unlike some past streaks of consecutive days with rainfall, the current streak hasn’t featured an unusual amount of rain.  Although a total of 4.03” of rain has accumulated at National Airport since April 27, there is a still a rainfall deficit of 0.24” in 2016 as of May 11.  That helps illustrate how dry 2016 had been prior to this record stretch of measureable rainfall.  The cloudy and rainy weather has also helped keep temperatures cooler than average on 12 of the last 15 days.

While the Mid-Atlantic Region has been cooler and wetter than average, there has been warmer than average weather across much of the central United States and cooler than average weather across a lot of the western United States.  Initially, this stagnant weather pattern was due to an “omega block” that causes the jet stream to flow in a pattern similar to the Greek letter “omega.”  It’s characterized by an area of high pressure that’s blocked by two areas of low pressure.  Areas of high pressure feature sinking air that suppresses cloud formation and promotes dry weather.  That’s acerbated the wildfires that have been getting headlines recently in the Canadian province of Alberta.

Conditions have also been conducive for a fair amount of severe weather in the central United States during the past few days.  From May 7 through May 10 there has been a preliminary total of more than 650 cases of severe weather – including roughly 50 tornadoes nationally.  That’s not unusual, though, since the United States averages more severe weather in May than any other month.  The DC Metro Region also experienced severe weather earlier this month.  On May 2, Rockville, Maryland saw hail 2.5” to 2.75” in diameter – roughly the size of a tennis ball.  That set a new record for largest hail in Montgomery County according to NOAA.

Despite being roughly four degrees cooler than average during the first half of May, temperatures can still rebound during the second half of the month.  It’s interesting to note that 90-degree heat has been felt at least once in the Nation’s Capital every May since 2010 so summer-like heat can arrive quickly this time of year.  By the time the hazy, hot and humid weather characteristic of July and August arrives many area residents will remember this cooler and wetter than average weather quite fondly.