One Year Later: Reflections on the Loss of Tim, Paul, and Carl

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It’s been a year.  In one way, that’s very easy to believe, because so much has happened.  Some of it has been negative, but most of it has been positive.  I’ve made new friendships and deepened others.  The numbing fog of loss has given way to hopeful – but sober – clarity.  Yet, in many ways, there is still a certain unreality about what happened.

Did we really lose Tim, Paul, and Carl?  It all feels a bit illusory still.  I replay the events over and over in my mind.  But, for some reason, it becomes less real – not more.  I know the story through and through, but full acceptance remains elusive.  I suppose that’s true for almost any traumatic loss.

And, I’m certain there are other impacts that I can’t quite see, because I’m in the thick of them.  I don’t chase storms the same way anymore.  I don’t think about tornado victims the same way anymore.  I don’t think of friendship the same way anymore.  So much has changed.  And yet, I feel that the changing isn’t near done.

But I think that this is good.  The smelling salts of tragedy are not pleasant, but they can be beneficial.  Feeling the impact of extreme loss can afford the sobriety that causes one to treasure the gifts that remain.  I know, for my part, that I cherish my relationships with my family and friends more than ever.  It’s a direct result of experiencing the loss of Tim, Paul, and Carl.  And while I would – as my friend Marc Austin puts it – trade all the tornadoes I’ve seen if it would bring them back, I know that my life is all the better because of what happened.

And yet, I still miss them.  I can still hear Carl trying to talk me into chasing the next setup, his cheery voice almost convincing me to join him.  I can still hear Paul talking hopefully about his ambition to become a movie maker, and me not doubting for a minute that he would succeed.  And I can still hear Tim talking about tornadoes of antiquity, and feeling that I had found a kindred spirit.  I wish I’d had more time with them.  But I thank God for the time I was able to spend with them.

“There is nothing that can replace the absence of someone dear to us, and one should not even attempt to do so. One must simply hold out and endure it. At first that sounds very hard, but at the same time it is also a great comfort. For to the extent the emptiness truly remains unfilled one remains connected to the other person through it. It is wrong to say that God fills the emptiness. God in no way fills it but much more leaves it precisely unfilled and thus helps us preserve — even in pain — the authentic relationship. Furthermore, the more beautiful and full the remembrances, the more difficult the separation. But gratitude transforms the torment of memory into silent joy. One bears what was lovely in the past not as a thorn but as a precious gift deep within, a hidden treasure of which one can always be certain.” –Dietrich Bonhoeffer

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Clarification of El Reno Tornado Width Claim

It has come to my attention that the tornado width ascribed to the El Reno tornado in my previous post is not quite accurate.  On the topic, Josh Wurman writes,

“That is a ridiculous interpretation, out of context, of the observation that the width of 30 m/s winds at >100 m AGL sometimes extended for about 7 km and that the equivalent 50 m/s width was as wide as 5 km.  How those correlate to expected surface damage is unknown.  The paper has a long footnote saying that using these definitions as ‘width’ is very subjective.  The diameter of the large circulation was about 2 km, very large, but similar to other Multiple Vortex Mesocyclones (MVMC) that we’ve documented before.”

I believe the confusion lies in the definitions contained within the conference paper.  In the paper, Wurman seems to equate the multiple-vortex mesocyclone (MVMC) with the tornado itself, noting that an interior sub-vortex was “nearly concentric with the larger tornado / MVMC”  (Wurman et al. 2013, AMS Radar Conference).  The slash would seem to indicate the interchangeability of the terms “tornado” and “MVMC”.  However, this is not the case.  In an early online release of the BAMS article of this work, it is clear that the 7 km (4.3 mi) width is ascribed to the parent circulation, not the tornado.  My previous post has been edited to reflect this understanding.

Regardless, the 2.6 mile width will remain in the record books, according to the National Weather Service.

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10 Amazing Facts about the El Reno Tornado!

The El Reno tornado, shortly after development. Photo credit: Gabe Garfield

Video capture of the El Reno tornado
 (Gabe Garfield)

The weather radar conference is ongoing in Colorado this week, and one of the conference papers features some eye-popping statistics regarding the 31 May El Reno tornado.  This paper, authored by Josh Wurman and others, is titled “Preliminary Results from the ROTATE-2013 Season”.  Now,  for the facts …

  • Near Highway 81, the El Reno tornado achieved a peak forward motion of 55 mph!  This is comparable to the highest translational velocities of tornadoes ever observed by the Doppler on Wheels (DOWs).
  • After the tornado crossed Highway 81, the sub-vortices (smaller tornadoes) within the larger circulation grew to mammoth proportions.  The largest were bigger than the size of 3 football fields combined!  (Most parent tornadoes do not reach this size!)
  • As the tornado approached Highway 81, small vortices developed on the northwest side of the circulation and “fed” the circulation.  Similar vortex behavior was noted with the gigantic Seward, Kansas tornado (23 May 08).
  • The tornado displayed vortices on multiple scales, similar to matryoshka dolls.  This “tornado within a tornado” behavior was noted shortly before the tornado crossed 81.   At that time, the tornado had two prominent vortices: an inner vortex, about 150 yards in width; and an outer vortex, about 1.25 miles in diameter.  Wurman notes this behavior in other large tornadoes, including the Kellerville, Texas (8 June 95) and Harper, Kansas (12 May 04) tornadoes.
  • One of the most intense sub-vortices during the El Reno tornado translated at an incredible 180 mph!  Curiously, this sub-vortex was also stationary at times during its 2 minute life-span.
  • At 6:26 p.m., the DOWs measured a 255 mph gust in a sub-vortex just south of Interstate 40.  This exceeds the EF5 threshold by over 50 mph.
  • Given the fast translation of this sub-vortex, a stationary observer would have only experienced these maximum winds for 0.5 seconds.  Talk about acceleration!
  • Applying a theoretical model (Rankine vortex) to the tornado yields velocities between 290 and 330 mph!  Of course, this assumes the theory is a good model of the real atmosphere (among other caveats) – but still, it’s very impressive.
  • Officially listed at 2.6 miles in diameter, the El Reno tornado is the largest tornado on record.  But it might also be the largest tornado ever documented.  Using the 30 m/s wind threshold (and excluding the rear-flank downdraft winds), the tornado was an unbelievable 4.3 miles wide!!  (Even using a 50 m/s threshold yields a 3.1 mile wide tornado … unbelievable!)  For comparison, this is larger than the Mulhall tornado (3 May 99), which was the previous standard-bearer for behemoth tornadoes (2.8 miles in diameter using the 30 m/s threshold).

    EDIT: The 4.3 mile width in the paper refers to the parent circulation of the tornado, not necessarily the tornado itself.  It should also be noted that the 4.3 mile width was > 300 feet above ground level, not necessarily corresponding to the size of the tornado.

  • In addition to the gigantic cyclonic tornado, the El Reno storm simultaneously produced a strong anti-cyclonic tornado.  This tornado featured powerful sub-vortices (potentially, the first ever documented) with winds peaking around 145 mph!

(Here is my video of the El Reno tornado.)

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May 3, 1999: My Story

May 3, 1999.  To those outside of Oklahoma, this date means very little.  But to those Okies who survived the largest tornado outbreak in state history, “May 3rd” is forever branded into our collective conscious.  That day over 60 tornadoes swept across the Southern Plains, with the vast majority in central Oklahoma.  Many of the tornadoes were strong, and at least 4 were violent (F4/F5).  Most people remember the Bridge Creek / Moore tornado, which still holds the world record for highest wind speed on Earth (~300 mph).   That tornado lasted well over an hour, and claimed the lives of over 30 people.  Interestingly, that tornado was really only the beginning of the outbreak, as many more tornadoes occurred well after dark.  The most impressive of these was the Mulhall tornado, which was well over a mile in diameter; based on mobile radar data, it was probably more intense than the Moore tornado.  The following is my story from that day.

F5 tornado near Bridge Creek, Oklahoma on May 3, 1999.  Photo Credit: Julianna Keeping, Newsok.com.

F5 tornado near Bridge Creek, Oklahoma on May 3, 1999. Photo Credit: Julianna Keeping, Newsok.com.

It was early May in 1999, and I was finally sniffing the scent of summer freedom.  Finals would occur in a little under two weeks, and I couldn’t have been happier.   It was Monday and, as was my custom, I ate lunch with my best friend Robert at the Norman High stadium.  We referred to it as “The Top of the World”, as we were able to enjoy the early spring breeze – and a sense of separation from the other students.  It was our hideout – the meeting place of our not-so-secret society.

But that day, we began to feel a little restless.  The weather was warm and muggy, and we had a case of the Summer Itch.  “We haven’t skipped class in a while,” I mused.  “No, we haven’t,” Robert agreed.  “Why not skip today?  We won’t be able to next week…” I suggested.  Robert quickly agreed and we set off on foot (neither of us had cars), as the lunch hour was coming to an end.  “Which direction should we go?” Robert asked.  I indicated that “north” seemed a good direction to me.  And so we went.

After a half an hour of (somewhat) aimless walking, we arrived at the intersection of Berry and Robinson streets.  From there, we could see the North Base, where the Norman Weather Forecast Office (Norman WFO) was located at the time.  My dad worked for the Operational Support Facility (OSF), and he often spent time at the WFO.  I don’t know why I thought it was a good idea, but I suggested that we go say “Hello” to my dad.  Somehow, I figured he wouldn’t be bothered by my ditching class.

When we arrived at the WFO, we were greeted by an OSF engineer, who looked a bit surprised that a couple of young neo-hippies had entered.   I inquired about my father, but he indicated that he was not at the North Base that day.  “You guys college students?” he asked.  “Nah, we’re in high school,” Robert replied, guitar case in hand.  “… On a field trip,” I added.   This wasn’t entirely a lie, as we had, in fact, crossed a field to get there.  “Well, would you like to take a tour of the Weather Service?” he asked.  Of course we would!  After all, what else did we have to do?

The engineer left the room momentarily to ask about a tour.  We waited patiently.  A few minutes later he came back with a look of regret on his face:  “Sorry, guys.  I guess the Weather Service folks are going to be a bit busy today with severe weather.”  “Are they expecting tornadoes?” Robert asked.  “I don’t know.  I actually don’t think we’ll see many tornadoes today.  Tomorrow should be the bigger day…” he replied.  With that, he gave us the card of the meteorologist-in-charge, and said that we should give him a call sometime to get a tour.  As we left, I distinctly remember the last thing I saw at the WFO that day: an image of the Red Rock tornado, a violent tornado that struck northern Oklahoma in 1991.

After leaving the WFO, we decided to head west from there.  And west, as Normanites know, is the direction of the Max Westheimer airfield.   It was quite hot and humid that day, so we decided to take a rest from our walking and play a little guitar.  We found a runway overgrown with weeds, and assumed that no planes would be taking off from there that day.  After a few minutes of playing Peter, Paul, and Mary’s “The Very Last Day,” we noticed a yellow security vehicle approaching us from the airport terminal.  Its lights were flashing.  Uh oh.  We briefly pondered making a run for it, but reasoned that that would make us look decidedly guilty.   So we stayed.

The security vehicle arrived and a middle-aged gentleman stepped out.  “You boys realize that you’re trespassing on airport property?”  We indicated that we knew.  “Did you realize that trespassing on airport property is a federal offense?”  We shook our heads, “No, sir, we did not know that…” as the gravity of the situation came to bear on us.  “I’m going to have to ask you to come back with me to the terminal.” Terminal – how fitting: the place where our lives would terminate!  Not only were we skipping class, we had just committed a federal offense!  He motioned for us to climb into the back of the pickup truck.

Upon arriving at the terminal, he asked us to wait while he went inside.  We once again contemplated making a break for it.  Again, we decided against it.  Two minutes later, he came back with two 20 ounce Cokes.  He handed them to us and said, “Guys, don’t do that again.”   We hurriedly assented to his request, took the frosty beverages, and set off, marveling at our good fortune.

After a bit more walking, we came to Andrews Park.  We relaxed there for a while longer, as we had grown weary from our travels.  It was about 3 p.m. then, and little did I know that the first storm of the day was attempting to initiate 100 miles to our southwest.  The sky was overcast – a thick canopy of cirrus had overspread the area.  Even so, it remained preternaturally balmy.  I mentioned to Robert that it felt like tornado weather; he agreed.

We arrived back at school just in time for the last bell, and found our rides home.  Along the way, I did my best to avoid revealing to my mom that I had not been in school.  As soon as I got home, I turned on the television.  Sure enough, a tornado watch had been issued.  As the evening progressed, I watched the outbreak unfold on television.  I went with my mom to pick my dad up from work, hoping to convince him to take me storm chasing.  But he was worried that Storm A (as it was later named) would come into Norman, and he felt an obligation to stay with our family (and, especially, an elderly neighbor).  I was incredibly disappointed, and I continued to plead with him, but to no avail.

We ended up taking shelter at the OU Student Union, and I remember watching the television coverage from the CBS affiliate.  Many college students stood there, their eyes glued to the TV sets.  Reports of a large tornado southwest of Norman came in, up to a mile wide.  I couldn’t even fathom it.  I wanted to see the tornado, so I left the TV room to go to the parking garage.  At the top of the parking garage, I still couldn’t see anything, since the trees were too high.  Additionally, the cloud bases were too low.  Disappointed, I returned to the TV room.

By that time, it was clear that Norman would be spared, as the large tornado was beginning to tear through southwest Oklahoma City.  Realizing our relative safety, we left the Union.  We turned on the radio, and heard ominous reports of incredible damage in Moore.  I could barely comprehend the magnitude of what was transpiring.  To the south, I noticed a new storm had violently erupted skyward – almost as if a nuclear weapon had detonated.  This would become the Stroud storm.  To this day, I cannot recall seeing more explosive storms.

Back at home, I was still sore about not getting to see the tornado.  My dad, sensing my disappointment, decided that we should take a family trip to see the next storm, Storm B.  We headed west on Highway 9, and went up to the intersection of Highway 9 and Interstate 44, just north of Newcastle.  Little did we know that F5 tornado damage lay less than a half mile to our west.  From that location, we could see a highly-sheared supercell thunderstorm to our northwest.  Unfortunately, it was just too hazy to see the multiple-vortex tornado that was being reported near Minco.

We went back home, and I watched television coverage for the rest of the night.  The outbreak was in full force, but most of the TV coverage focused on the disaster that had just struck Oklahoma City.  Finally, around 11 p.m., I went to bed, marveling at what I had experienced that day.

What was your May 3rd experience?

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Day 3 Moderate Risk: Reasons Why It Could Be Huge … Or, Hugely Disappointing

Day 3 Outlook from the Storm Prediction Center.  Valid: Wednesday, April 17th.

Day 3 Outlook from the Storm Prediction Center. Valid: Wednesday, April 17th.

As most chaser types already know, the Storm Prediction Center has issued a moderate risk for severe weather for Wednesday.  A significant severe weather event is expected, but the kind of event is still uncertain.   Will it be a wind and hail day with a few tornadoes?  Or, will it be a full-scale tornado outbreak?  Or, more likely, will it be somewhere in-between? It’s still too early to say, of course.  And, as usual, many will dogmatically assert their favored position, but the truth is that we just don’t know yet.  Here are a few reasons why Wednesday could be huge, and a few reasons why it could be a dud.

Reasons Why Wednesday Could Be Huge

  • Strong upper-tropospheric trough entering the Plains – this will set the stage for robust moisture advection, strong low-level shear, and the transport of the elevated mixed layer off the High Plains (and associated steep lapse-rates).

    500 mb forecast for 00Z 18 April from 12Z 15 April NAM.  Twisterdata.com

    NAM 500 mb forecast.  Valid: 00Z 18 April.  Initialized: 12Z 15 April. Twisterdata.com

  • Strong instability – the elevated mixed-layer looks primed – as it has all season – to generate strong instability.  Finally, rich moisture – almost 200 mb deep – will exist with it!  You can see this when toggling between the forecast CAPE and the forecast mixed-layer CAPE: they’re virtually the same.  Of course, this assumes that morning storms will not interfere with daytime heating.

    CAPE forecast for 21Z 17 April from 12Z 15 April NAM.  Twisterdata.com

    NAM CAPE forecast.  Valid: 21Z 17 April.  Initialized: 12Z 15 April NAM. Twisterdata.com

  • Incredible hodographs– in spite of the screwy nature of the upper system (from a pattern-recognition standpoint), the hodographs look bodacious.   Very strong low-level shear should develop as early as noon, owing to the development of a 40 – 55 kt low-level jet.  As a result, the classic “sickle-shaped” hodographs – associated with most major tornado outbreaks – are forecast to develop.

    NAM forecast hodograph for Gotebo, Oklahoma.  Valid: 00Z 18 April.  Initialized: 12Z 15 April.  Twisterdata.com

    NAM forecast hodograph for Gotebo, Oklahoma. Valid: 00Z 18 April. Initialized: 12Z 15 April. Twisterdata.com

  • Chaser-friendly storm motion – normally, storms move quite fast in 50 kt flow at 500 mb.  However, the low-level flow will be quite backed, which will slow the storm motion some (read: quite chaseable!).

Reasons Why Wednesday Could Be Disappointing

  • Weak cap / instability – the potential is there for some big CAPE, but will it materialize?  The cap is forecast to be weak, which could lead to the development of too many storms and a significant reduction in instability.
  • Poor phasing of parameters – generally, you look for negatively-tilted troughs for big tornado outbreaks, since the low-level shear is usually stronger in those cases (because of backed low-level flow) and the storm mode tends to be more favorable (because of the favorable orientation of the shear vector to the axis of the convecting boundary).  This system will be positively-tilted, which is generally associated with lesser events.  Will it matter?
  • Unfavorable storm mode – will a weak cap allow storms to develop early, leading to the early development of a mesoscale convective system?  Or will storms tend to “seed” each other, prompting the development of chaser-unfriendly high-precipitation storms?  Or will storms find optimal spacing, allowing for the development of multiple classic tornadic supercells?  These questions probably won’t be answered until the day the event occurs.

What do you think is the most likely outcome?

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Tornado Season is Here (and 5 Essential Steps to Stay Safe)

Spring is arriving.Image credit: stock.xchng

Spring is arriving.
Image credit: stock.xchng

It’s April, and if you live in the south, the gray pallete of winter is slowly – but perceptibly – changing into a cornucopia of springtime color. It’s warmer now (at last!), and most of us are happily trading the drudgery of overcast, barren trees, and overcoats for the long-awaited promise of blue skies, blooming flowers, and, of course, short sleeves. Even still, this bourgeoning beauty is accompanied by the barely-subconscious understanding that such seasonal delight comes at a price: severe weather.

Every spring, thousands of powerful thunderstorms sweep across the plains of the United States, leaving considerable mayhem and excitement in their wakes. Severe wind storms toss trash cans and trampolines into the streets, while leaving an inconvenient mess of tree branches in front yards. Hail storms cause quite a flurry, too, as folks rush about, trying to avoid the untimely christening of new vehicles. And, of course, the “flash” and “boom” of lightning and thunder never fail to frighten their fair share of small children and yippie dogs. But more often than not, these storms – like the scary-looking-but-relatively-benign beasts of Monster’s Inc. – cause more good than harm, leaving behind copious quantities of beneficial rain.

A violent tornado striking Joplin, MO.  Photo Credit: Twisterchasers.com

A violent tornado striking Joplin, MO.
Image credit: Twisterchasers.com

Residents of Joplin, Mo, after a violent tornado hit the southwest Missouri city, May 22, 2011.  Photo Credit: AP Photo.

Residents of Joplin, Mo, after a tornado hit the southwest Missouri city, May 22, 2011.
Image credit: AP Photo

Even so, there remains the collective understanding that these powerful forces cannot always remain so benevolent. The forces of nature are simply too raw, too unbridled. And, in rare fury, they unleash straight winds that can lift the roof off your house, hail that can punch holes through your car’s windshield – and tornadoes that are capable of sweeping your house off its foundation. These are the storms that people talk about for years – even decades – after they occur. These are the Joplins (right), the Tuscaloosas, the Moores - front-page-grabbing events that evoke shock, awe, and horror. Observers near and far may experience a profound empathy, a numbing feeling of fatalism, or a discombobulating sense that, perhaps, these storms have no larger meaning. These are the scenes of war-zone-like macabre, with no one to prosecute.

And these are the storms that create jobs for weather people, like me. The horror of these storms spurs action, and savvy politicians use the moment to mutual advantage. But most meteorologists are not opportunists. In fact, many of us entered the profession because of just such a mega-storm. For me, it was 1990, when a strong tornado hit my hometown of Stillwater, Oklahoma. Then, tornadoes were simply terrifying. But I soon discovered the key to quelling fear: knowledge. As I grew older, I read as much I could find on tornadoes. And the knowledge was freeing: fear led to fascination, and fascination, to understanding. And it is this understanding that I wish to share with you.

Tornado Alley: Average number of tornadoes per year.

Tornado Alley: Average number of tornadoes per year.
Image credit: Oklahoma Climatological Survey

First, a warm blanket: as scary as violent tornadoes are, they are very rare. These worst of tornadoes (EF4/5) account for only 2% of all tornadoes in the United States1. Even in the heart of Tornado Alley (right), a single location may experience such a tornado only once in a 10,000 year period2. That means you could live over a hundred lives in Oklahoma and never experience a violent tornado. Nevertheless, these storms are responsible for a disproportionate fraction of tornado deaths1 (67%). To be sure, it isn’t a lottery you want to win. The good news is that you can vastly increase your probability of survival, even in the worst tornadoes. Read the following to do just that.

Steps to Severe Weather Safety

  1. Review tornado safety tips. It’s obvious, but if you don’t know what to do during a tornado, it will be difficult to survive. Review tornado safety procedures at the beginning of every storm season.
  2. Make a plan. If a violent tornado is headed right for you, it’ll be tough to think straight. Making a plan ensures that most of your thinking is done before that happens. Ask yourself these questions, and envision potential worst-case scenarios.

a. How will I stay informed before and after a tornado?
b. For whom am I responsible?
c. Where will I go if a warning is issued?
d. What will I need during and after a tornado hits?

  1. Build an emergency kit. Related to Question D, knowing what you will need during and after a tornado hits is crucial for survival. Food, water, first-aid kit, and boots are just some of the items you’ll need after a tornado hits.
  2. Know the forecast.  To be prepared for tornadoes, you need to know when they are possible.  First, check the Hazardous Weather Outlook from your local National Weather Service office to monitor for upcoming severe weather.  When severe weather is expected, you should also check out the severe weather outlook from the Storm Prediction Center (SPC); this team of severe weather experts produces daily forecasts for the entire country, and it’s a tremendous resource.  Finally, on the day of the potential event, you will want to check the forecast from your local weather office for severe weather updates.
  3.  Receive the warnings.  All of the previous tips are great, but if you don’t know when you’ll need to take cover from a tornado, they won’t be of any use to you.  There are many ways to receive the warnings, and most of them are good: local television, social media, weather radio, radio, and word-of-mouth are just some of the ways you can get the warning.  In particular, I would recommend that you purchase a NOAA Weather Radio.  When a tornado warning is issued, a very loud tone will alert you (if you’re asleep, it will wake you) that a tornado is threatening, followed by a direct warning message from the National Weather Service.  They are readily available at local stores.  Also, if you have a smart phone, I would recommend the iMap Weather Radio app.  It has many of the features of a weather radio, and a few additional ones too.  However, I would still recommend that you purchase a weather radio, since it will certainly wake you if a tornado warning is issued at night.

If you have any questions about tornado safety, don’t hesitate to ask!  I’d be more than happy to answer!

Sources:

1. Concannon, P., H.E. Brooks, and C. Doswell: “Climatological risk of strong and violent tornadoes in the United States.” 2001. http://www.nssl.noaa.gov/users/brooks/public_html/concannon/

2. Meyer, C., H.E. Brooks, M.P. Kay: “A hazard model for tornado occurrence in the United States.” 2000. http://www.nssl.noaa.gov/users/brooks/public_html/papers/meyeretal.pdf

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Tornado Outbreak Next Week?

This storm season has been underwhelming, to say the least.  Only 153 tornadoes have been reported this year, which is a little more than half of the normal value (Image 1).

Image 1: Monthly trend in tornado reports.  Source: The Storm Prediction Center.

Image 1: Monthly trend in tornado reports. Source: The Storm Prediction Center.

What gives?  Well, during the month of March, multiple cold frontal passages removed the rich, “high octane” moisture of the tropics (necessary for explosive supercell thunderstorm development) far from the Plains.  Accordingly, storm chasers lamented, with some openly wondering whether or not to stick a fork into 2013.   Thus, when a big upper trough appeared in the West in the long-range models (Image 2), chasers were thrown into a frenzy of spring-time excitement.

Image 2: Mid-tropospheric trough on Monday, 8 April, as forecast by the 12Z 3 April GFS.  Source: twisterdata.com

Image 2: Mid-tropospheric trough on Monday, 8 April, as forecast by the 12Z 3 April GFS. Source: twisterdata.com

While the details about this system remain muddy – the big picture looks quite tantalizing.  In particular, the global models suggest the development of a broad, strong upper-level low over the western United States that will induce strong, southerly low-level flow and associated moisture advection over the central U.S.  Unlike previous events this year, the moisture quality looks quite decent – courtesy of a nice Caribbean fetch (dewpoints at or above 60 F, perhaps over 65 F at some locations, depending on the model; Image 3).

Image 3: 12Z 3 April GFS forecast of dewpoint temperature for 00Z 9 April.  Source: twisterdata.com

Image 3: 12Z 3 April GFS forecast of dewpoint temperature for 00Z 9 April. Source: twisterdata.com

Given the mean westerly flow this spring – and drought conditions – the elevated mixed-layer also looks primed to create strong instability; indeed, the 12Z 3 April GFS forecast shows over 3500 j/kg in western Oklahoma/western north Texas by Monday evening (April 8th; Image 4).

Image 3: 12Z 3 April GFS forecast of CAPE  for 00Z 9 April.  Source: twisterdata.com

Image 4: 12Z 3 April GFS forecast of CAPE for 00Z 9 April. Source: twisterdata.com

Nevertheless, the severity of the event remains uncertain.  In particular, the timing of upper-tropospheric waves could be the difference between a decent chase day – and a major tornado outbreak.  As usual, exiting waves would lead to less-than-ideal hodographs, while an entering wave would create the familiar “sickle-shaped” hodographs present during major outbreaks.  In all likelihood, though, the timing of the waves won’t be resolved until the event is within 24 hours.

Also of some concern is the quality of the moisture return.  While the GFS continues to insist on high-grade moisture (65 F isodrosotherm near the dryline by game time), the Euro is significantly less bullish (only lower 60s F Tds).  Even if the Euro is correct, tornadoes would still be in the cards, though the event might be less significant (unless the wind fields are stronger than forecast).  It will certainly be interesting to see which model is closer to reality – although we may not get a feel for this until the day before the potential event.  We’ll see!

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