Tuesday, May 12, 2015

May 9, 2015 cold core tornado setting over eastern Colorado

I haven't done a weather analysis blog post in nearly 3 years (wow, long break!).  But Saturday's picturesque cold core tornado event (5/9/15) in eastern Colorado prompts me to do a short write up.

I've heard from several people who didn't realize this was a cold core setup, so I'll present a few maps to show that it was.  Just click on each image below to see it larger.

First, the surface pattern (3 surface maps below at noon, 3 pm, and 6 pm MDT) was a fairly classic cold core surface low pattern with several boundaries converging into the low... the dryline/pacific front (dashed brown), the warm front (red solid), and the cold front/occluded front (blue and purple solid):

Second, what made it a true cold core setting was the close proximity of the strong 500mb closed low (NAM 9 hr forecast for 21 UTC/3 pm MDT) over Colorado:

Notice the 500mb cold air aloft (dark blue) coming out over the warm sector in eastern Colorado and western Kansas.  The graphic above also shows the enhanced storm-relative helicity (SRH, a source of low-level storm rotation) forecast over eastern Colorado north of the surface warm front (circled).

Given the cold air aloft over the relatively warm surface air with dew points in the low 50's F and easterly surface winds, the stage was set for rapid upward stretching and tilting of horizonal vorticity ("spin") associated with the 0-1 km SRH, for possible tornadoes.

The graphic below shows the location (arrow) on satellite of the storm of interest north of Lamar (see also the circled "S" on 2107 UTC surface map earlier) that encountered the increased SRH as it moved north with the 500 mb winds across the warm front seen in our earlier surface maps:

With subsidence (descending stabilized air) over western Kansas in the wake of the midday storm cluster there, this cell was the easternmost and primary cell to take advantage of the warm frontal zone in a favored location just east of the surface low. 

The accompanying radar image above is a couple hours later as the supercell produced a large tornado (see photos below), before being undercut by the cold front/occluded front (radar "fine line", see arrows above) around 6 pm CDT as it moved north into the cold air.  

Another clue that this was a cold core setting is the smallness/compactness of the supercell, allowing for getting the whole storm and tornado into the first photo image above (by my wife, Shawna).  Many (if not most) tornadoes associated with cold-core 500 mb lows are small and weak, but this day saw at least one large long-lived tornado due in part to the strong dynamics from the big upper low nearby within a full longwave trough in the jet stream.

I should mention that the midday storm cluster and outflow over Kansas on Saturday would have killed most settings regarding tornado potential.  But with cold core patterns like this, the atmosphere can recover quickly with the very cold air aloft if there is sun's heating and dew points in the low 50's F, particularly over elevated terrain like eastern Colorado. Cold core settings are also just about the only pattern where you can get tornadoes with a supercell only 60-80 miles from accumulating snow, as was happening near Limon/Denver northwest of the surface low.

A truly fascinating day, with the best part being that the tornadoes occurred over wide open country without damage or injury.

Jon Davies - 5/12/15

Monday, June 24, 2013

An essay by Shawna Davies on media & public response problems in Oklahoma City on May 31, 2013

What we saw in Oklahoma City the evening of May 31st really bothered my wife Shawna and me.  At her request, I'm publishing her essay about that night, to help process the experience, as well as make positive suggestions from it.  Thanks, Shawna.. you have my full support.  Here's the essay:

“It was a dark and stormy night…”  This famous quote at the start of British author Lord Lytton’s 1830 novel Paul Clifford was used often by Charles Schultz in his “Peanuts” comic strip, as well as by novelists struggling with “writers block.”  But it has never rung so true to me, as I struggle to begin this essay.  Nearly a month after the deadly May 31st, 2013 tornadoes and flooding in central Oklahoma, I still feel a strong need to write about the near-catastrophe of media communication and public anxiety that day in Oklahoma City.  
I was there that evening.  My husband Jon is a severe weather researcher, and I do severe weather awareness outreach; we are also both storm chasers.  Between us, we have over 40 years combined experience with severe weather events, and have seen a great variety of situations.  However, even with all our knowledge, experience, and awareness as chasers, what we encountered on the roads that night in Oklahoma City was in a league all its own. 
Observations from the “Highway of Hell”
At around 7 pm, after the massive El Reno tornado that killed 8 people, we were in southwest Oklahoma City attempting to retreat southward from the same storm complex.  As winds from a new rain-wrapped storm circulation blew across on Hwy. 4 (the only route south from our location), we encountered bumper to bumper traffic stretching for miles, with hardly anyone moving!  My first thought was that these were storm chaser “hoards”, but there were too many cars.  My second thought was that perhaps a concert or some other venue had let out due to the weather.  However, we soon noticed cars dangerously passing us on the right shoulder, then on the left by crossing the median, some even driving south in the NORTHBOUND lanes.  I looked closely at the faces in the cars around us; it was soon quite obvious they were locals, and they were panicked.  My third (and correct) thought was, “These people are fleeing town!”  Click on the image or link below to watch video as we were stuck in this exposed-to-the-weather traffic:
Another rain-wrapped circulation (not tornadic, thankfully) passed near us as hundreds of cars crawled slowly southward on Hwy. 4.  The next hour was quite hair-raising and very frustrating, with what seemed like thousands of people sitting on the open highway as tornado warnings were issued both left and right of us.  Fortunately, no strong tornadoes came down upon the city at that time, or simply put, it would have been a massacre.
During the next morning’s drive back to Kansas City, I kept thinking about that frightening night.  Texting and talking to friends, I heard that at least one local TV meteorologist had told people to flee if they did not have underground shelter.  I was so angry - the death reports were starting to file in by then – that I posted this on my Facebook page:

Someone forwarded me a link of a portion of Mike Morgan’s KFOR broadcast from that evening, where I indeed heard him tell people to flee south ahead of the El Reno storm as it approached Oklahoma City.  It’s true that a new but weaker tornado did damage near the airport and over southwest parts of the city just north of where we had been stalled in traffic.  But after our experience in the traffic jam, I was truly stunned that he had told people to flee their homes in a large metropolitan area!  However, my feelings quickly shifted in another direction when we soon learned of the deaths of 3 tornado researcher friends, which took precedence over other issues during the next two weeks.
Since then I’ve reviewed that clip several times and have read many articles and viewer comments regarding Mr. Morgan’s broadcast warnings.  (To read some qoutes from Morgan's KFOR coverage, see this article here.)  Much has been said about the actions that some citizens took, and there has been debate about responsibility for the deaths of one family that took cover with other residents of a nearby apartment complex in a large storm drainage culvert. (Read this NewsOK.com article here.)

Who is responsible? 
The question of responsibility regarding these flooding deaths during the May 31st, 2013 event has puzzled me.  On one hand, Mr. Morgan did a great job during the May 20th Moore tornado, and, apart from telling people to "flee", I feel he did a reasonable overall job on Friday evening May 31st.  It is true that Morgan has covered many tornadoes over the years, and he is human like us all; he may have been somewhat tired and overwhelmed, particularly given the elevated local anxiety from the recent Moore event.  And now another large tornadic storm was approaching Oklahoma City from the west. 
On the other hand, I do feel strongly that he should not have told people how to take shelter at the last minute, particularly his suggestion that people without underground shelter get in their cars and "go south".  Viewers know that on-air meteorologists are there to supply warning information during weather.  But it is up to citizens themselves to be aware and know what specific actions to take in advance of potentially dangerous conditions  - especially in high risk tornado and / or flooding areas.  It is their responsibility to decide on the best shelter BEFORE severe weather strikes.  The above article from NewsOK highlights this issue.  There was debate in the family about whether they should seek shelter inside the apartment complex, or leave and head to the storm culvert at the last minute.  As a severe weather preparedness and awareness advocate, I find this incredibly sad and frustrating. 
Regarding weather, I have observed over the years that most citizens only want to know, “Will it rain at my wedding or picnic?” Or, “How hot or cold will it be so I know how to dress today?”  When people do pay attention to severe weather events, they do so because:  A) They have had ‘close calls’ in the past that frightened them enough to pay attention, or B) they are weather enthusiasts who have a natural interest.  Most others have what sociologists call “optimism bias” or an “it-can’t-happen-to- me” attitude, so they do not pay attention until it is staring them in the face.  Therefore, it is no surprise to me that people took Mr. Morgan’s word and did as he said… flee!
Do I think Mr. Morgan or KFOR is liable?  I have no idea; I am not an attorney.  However, (and with all due respect to the deceased), he never did say “go into a storm drain or culvert”.  But, again, he should take responsibility for telling citizens to “flee”, and perhaps apologize, explaining the situation for the sake of public trust and future lessons that can be learned.  Clearly, suggesting that people near or in a large city flee a tornado in their cars can result in massive traffic jams and a deadly recipe for disaster.
What can we learn from this deadly event?
·      FOR THE PUBLIC:  As many friends and colleagues in the weather community know, when it comes to educating the public about taking responsibility and learning basic tips to increase chances of surviving severe weather, especially tornadoes, we still have a long way to go.  A  famous quote says, “You can lead a horse to water, but you can’t make him drink”.  Very true, but we must still continue to lead, for at least some people will drink.  We also need to continue to push for the public to invest in safe rooms or underground shelters in tornado prone areas – such as the Oklahoma City and Moore – as well as investing in phone apps and weather radios to stay well informed.  The same goes for state and local governments regarding public places such as schools, outdoor facilities and so on.  Lastly, we also must also continue to preach about staying informed ahead of time, so that citizens are not caught on the road; DO NOT take cover under overpasses or in flood-prone areas.  On May 31st, I saw cars packed in on both west and east lanes under an overpass, even parked all the way up close to the girders (I’m amazed some didn’t roll down embankments!). 

·      FOR THE MEDIA:  On-air people must be very careful about their wording of warnings.  It’s their responsibility to properly warn as fast and direct as possible to give people time in the path of tornadoes to find adequate shelter.  But citizens must use their own common sense to decide what is “appropriate shelter” for each living circumstance – you can’t make that decision for them!

From available information, as of this date, 20 people perished (with one child still missing) on that evening from tornadoes or flooding, and two additional people died from flooding the next day.  My hope in writing this essay is to emphasize that one casualty is too many, and we all must learn and spread the word from this event to prevent other tragedies.  I hope that we continue to improve our already excellent severe weather watches and warnings, and that all involved with storm chasing and meteorology will seriously continue to teach and educate citizens concerning responsibility during severe weather events.

- Shawna Davies 6/25/13

Tuesday, June 4, 2013

The El Reno tornado - unusual & very deadly

NWS released new information on Friday's tornado near El Reno OK, rating it EF5, and showing it to be a record width (2.6 miles).  The map above shows the updated path, and the damage track from satellite (inset).

With the death toll now reaching 19 people, it was truly a dark and tragic day.  I've been trying to make sense of what happened, and today's information along with a careful analysis of radar data offers some clues.  The mesocyclone and tornado appeared to be "arcing" around a pivot point within the larger storm cell, and as it curved northeastward, it accelerated significantly.  As some chasers have pointed out online, a simple analysis from conventional radar data of the movement of the storm-relative velocity couplet shows that the tornado, along with getting wider and more intense, increased it's forward speed from 20-25 mph to over 40 mph for a time (see speed annotations on the map above).  This unanticipated movement may help explain why so many storm chasers were caught suddenly in the path, including the tragedy of Tim Samaras and his crew (see my prior post).

The map above also shows the location of 3 images that Shawna and I took while approaching the tornado and then moving south out of its way. The first image below shows the tornado in its early stages illuminated by lightning to our west-southwest:

This next image shows how hard it was to see the tornado at times, wrapped in rain curtains and poor contrast when it was about a mile to our west.  This was truly frightening, and we high-tailed it to the south well out of its way.

This last image is from 2 miles south-southwest of the tornado when it was around 2 miles wide, looking like a large ghostly wall cloud on the ground:

I hope this tornado case forcibly reminds us that many tornadoes aren't always visible, and that they don't always move and behave the way we expect them to, even for the experts.  Friday was a sad, scary day.

When I get time down the line, I'll try to post some more analysis about this case.

- Jon Davies  6/4/13

Sunday, June 2, 2013

Tim Samaras, Carl Young, and Paul Samaras

                                       photos of Tim Samaras above by Jon Davies (c) 2005

My wife Shawna woke me this morning to tell me my researcher friends Tim Samaras and Carl Young, and Tim's son Paul were killed in Friday's tornado near El Reno OK.  I am in shock and deep sadness. My heart truly goes out to Tim's wife Kathy and his family.  My condolences go out to Carl's family as well.  I can not imagine...

My blog has been on hiatus due to family stuff and selling a house over the past year.  The last post I made was about Tim's lightning research article in Nat Geo magazine this past August.  Now sorrowfully, this.

I don't know the exact circumstances, but the roads were very crowded on Friday.  As Shawna and I watched the rain-wrapped tornado to our north, changing direction from southeast to northeast near El Reno and highways 81 and I-40, we were quiet.  At one point earlier, Shawna had even said, "I'm afraid some chasers are going to die today."  I would never have believed it would be Tim and Carl and Paul.  

I can only imagine that they got caught in the chaser and local congestion as the hard-to-see tornado suddenly moved leftward.  Tim and Carl were gentlemen, very considerate/ compassionate people, always balancing chasing safety and setting a good example with their up-close research work.  They would have let others get out of the way on a crowded road before themselves, unlike some other "me first" people I saw driving on Friday.

There's something of a tendency to over-eulogize people when they pass on, but Tim and Carl were truly first and foremost a class act, willing to talk to anyone, not caught up in any storm chaser "celebrity". I always looked forward to seeing Tim and Carl.  And Paul was just coming into his own with humor and a passion for learning about storms, like his dad.  It goes without saying that Tim was a pioneering scientist and engineer, a ground-breaker, incredibly creative and cutting-edge.  I will always have the greatest respect for him.

One of the great experiences of my life was a 10-day period in June 2005 accompanying Tim and Carl on one of their expeditions funded by Nat Geo. We drove from Kansas to the Dakotas and back to Kansas and down to Texas, and then to Iowa, seeing so many tornadoes I lost count.  We came close on a couple probe hits, but what stays with me is Tim's boundless energy and focus and enthusiasm.  He and Carl were on another level than me, and they greatly inspired me in my empirical forecasting work.  I was extremely honored that they asked me to go with them.

My hope is that Tim's and Carl's and Paul's deaths with serve as a permanent reminder that storm chasing is serious serious business, and not the "fun/exciting" competitive game for notoriety that so many want to make it.  If smart, knowledgeable, dynamic scientists of Tim and Carl and Paul's character met their final encounter, it should make us pause.  Mother Nature is dangerous and unpredictable, and that should jolt us back to a huge respect for the forces of the atmosphere. It should also motivate us to continue emphasizing severe weather safety and great research, Tim's true distinction and legacy.

Tim and Carl and Paul have left an enduring mark on severe weather science forever, both professionally and personally.  I will miss them more than words can say.  

- Jon Davies 6/2/13

Friday, July 27, 2012

Lightning article featuring Tim Samaras in August National Geographic

As I wrote in this blog a month ago, I'm taking a break this summer from case study posts.  However, I do want to mention that National Geographic is running an excellent article on my severe weather researcher friend Tim Samaras and his lightning photography quest. 

The article and accompanying images are in the August 2012 issue of National Geographic magazine.  Here's the cover:

credit: National Geographic

And here are some images from the article, shown with National Geographic permission:

© Carsten Peter

© Carsten Peter

© Carsten Peter

Here's an online link to other photos:

A portion of Nat Geo's press release:

Using the world's fastest high-resolution camera housed in a mobile trailer, Tim Samaras hopes to be the first to photograph the micro-second event (not visible to the naked eye) that triggers a lightning strike. Through this, Samaras hopes to discover clues to some of lightning's biggest mysteries: Why will a lightning bolt sometimes strike a low tree when right beside it is a tall metal tower? And why, for that matter, does lightning strike at all?

He is used to having people tell him that what he’s trying can’t be done. But before he became obsessed with lightning, Samaras spent several years chasing after tornadoes to deploy electronic probes, mounted with video cameras and other instruments, to record what it looks and feels like from inside.  People were dubious about that too, but he managed to gather some of the most accurate readings ever of wind speed, barometric pressure, temperature, humidity inside a tornado vortex.

Congratulations, Tim...  As always, great work!

Jon Davies - 7/27/12

Saturday, June 30, 2012

Taking a break...

Wow... June has gone by and no blog posts.  I've had a lot going on personally the last month, and there's a bunch of stuff for me to work through the rest of the summer.

I'm going to continue to take a break to sort some things out.  Sorry about that.  I know I have a small loyal following of weather enthusiasts who like to read and learn about severe weather and forecasting.  I'll see if I can get back to posting some occasional case studies this fall.
For those who read my stuff, thanks so much for your patience.

Jon  6-30-12

Sunday, May 20, 2012

Prolific non-supercell tornado outbreak in Kansas 5/19/12 !!!

Yesterday (May 19) in south-central Kansas was a great reminder that potentially strong tornadoes (see images above near Rago KS in the 6:30-6:45 pm CDT / 2330-2345 UTC time frame) can occur once in awhile without the typical supercell processes that involve large low-level wind shear or storm-relative helicity.  I've written peer-reviewed papers on this subject for NWA Electronic Journal (2005, see here) and Weather and Forecasting (2006, see here).  In particular, the setting shown in the 2005 NWA paper with Jim Caruso matched what happened yesterday (which was largely unexpected) quite well.

Non-supercell tornadoes that we tend to call "landspouts" (because of their seeming similarity to waterspouts, but over land) generally occur on sharp boundaries and get their "spin" from stretching of vorticity associated with the sharp wind shift, often seen as a fine line on radar or even satellite (see the frontal boundary in south-central KS on the satellite image above).  While the boundary is the most important ingredient, the environment usually includes steep low-level lapse rates (a rapid drop in temperature above ground) in the lowest 1 or 2 km due to strong surface heating and no temperature inversion (little or no CIN or convective inhibition), along with well-mixed low-level moisture.  Such tornadoes can occur even if the spread between temperature and dewpoint is large and cloud bases (LCLs or lifting condensation levels) are quite high, unlike supercell tornadoes. Notice that the Rapid Refresh sounding above, 30-40 minutes before yesterday's first tornadoes, had all these characteristics.  Such a profile would promote rapid low-level upward stretching under storm updrafts, and if the stretching with thunderstorm updrafts were to occur directly over a wind shift boundary with vertical vorticity or "spin" along it, that would increase the chance of tornadoes.

The morning NAM and HRRR forecast panels above for mid to late afternoon on Saturday suggested that these ingredients (boundary, steep lapse rates, low-level moisture with little CIN, and convection on the boundary) might be in place for a "mesoscale accident".  Short-term forecasting of such set ups is never easy and depends on everything coming together just right.  But certainly, with so many tornado reports in the Kingman/Harper County area of south-central Kansas during the 90 minute period 5:30-7:00 pm CDT (2230-0000 UTC), including one tornado that significantly damaged wind farm turbines, everything came together in spades.

The surface map and SPC mesoanalysis panels above show these same ingredients coming together in real-time on the 2200 UTC panels before the tornadoes.

In contrast, the next SPC panels above include 0-1 km storm-relative helicity (SRH) at 2200 UTC, showing how poor the low-level shear environment was yesterday in regard to supercell processes.  However, the surface vorticity panel by it shows how much vertical vorticity was focused and available with the boundary for non-supercell processes.

The 3 radar panels above also show some interesting mesoscale features. Along with the storms "back-building" to the south-southwest like a "zipper" on and directly over the boundary (common in prolific "landspout" events), notice the southwestward-moving outflow boundary (another radar fine line) visible behind the frontal boundary. As this intersected the frontal boundary progressively southward, it appeared to help in the generation of successive tornadoes, including the tornadoes near Rago KS tornado that occured in northern Harper County KS about 15 minutes after the last image above.  I've seen this before in prolific landspout events when the radar is close enough to see it, and it could be an important issue in the production of stronger "landspout-type" tornadoes.

One other issue I will mention is the Non-Supercell Tornado parameter (NST, not shown) found on SPC's mesoanalysis site.  It performed _horribly_ yesterday, showing no values at all during the outbreak.  I'll have to look back at the ingredients that go into the NST parameter, but my impression is that it depends too much on the presence of low-level (0-3 km) CAPE, which may or may not be part of the environment in "landspout" settings (see the earlier sounding).  What's probably more important is well-mixed moisture in the lowest 1-2 kilometers along with the steep low-level lapse rates, and a lack of CIN (convective inhibition) and absence of a temperature inversion that might otherwise slow stretching in low-levels.  If I were writing the papers now that I referenced earlier, I would modify my description of these ingredients.

At any rate, as I've heard Chuck Doswell say many times, there are many ways to get a tornado.  Mother Nature doesn't care if the vorticity to be stretched is from SRH (tilted horizontal vorticity) or a sharp wind shift boundary (localized vorticity already oriented vertically).  A prolific non-supercell tornado setting like yesterday doesn't happen very often, but for tornado forecasters it is definitely one to get familiar with and watch for.

- Jon Davies  5/20/12

Update:  Wichita NWS (see here) has rated one of Saturday's tornadoes that struck a farm northwest of Harper as EF3 in intensity. That's pretty impressive for an event driven primarily by non-supercell tornado (NST) processes.  It seems that the more prolific an NST event and the longer it goes on, the more intense and "supercellular" in nature the tornadoes can become, particularly if deep layer wind shear is significant (around 35 knots in this setting).