Monday, May 30, 2016

Counting Tornadoes: Dodge City 24 May 2016 - How Many?

Most storm chasers count the number of tornadoes they see on any given day.  The bigger the number, the more "impressive" a chaser you are, I guess.  But many times, from a useful operational meteorological view, such "counts" are inflated.

Last Tuesday (May 24) near Dodge City is a good example.   I've heard several storm chasers tell me they saw anywhere from 10 to 17 tornadoes on the prolific tornadic supercell that moved from near Minneola across Dodge City, thankfully missing any direct hits on towns.

My wife Shawna and I followed the storm starting from a distance (near Bucklin, Kansas) up to fairly close just south of Dodge City.  I'm conservative regarding tornado counts, and we saw at least 4 "primary" tornadoes, each from its own mesocyclone cycle as new parent circulations developed north or east of each tornado, all fascinating to watch.  

Any other tornadoes seemed to be brief and transitional, including a rope tornado in the inflow to the 2nd primary tornado.  One of the mesocyclones just SW of Dodge City produced several visual "spin ups" with occasional multiple vortices before putting a fully condensed tornado on the ground.  But from a practical viewpoint, I would count that as one intermittent tornado circulation (again, same mesocyclone) instead of several individual tornadoes.

Following is  documentation of what we saw using video captures (some of these contrast enhanced to make it easier to see features).   All views are toward the west-northwest or northwest.

Not counting any brief early touchdowns we couldn't see, here's the first primary tornado touchdown northwest of Minneola, viewed from near Bucklin (25 miles away!) around 6 pm CDT, along with a wide view of the storm (Bill and Anna Stromberg were in the vehicle ahead of us):

This first tornado was on the ground around 25 minutes, and here are several images at various zooms.  Rain wrapping to the west of the tornado soon made it harder to see, and a new lowering (at right) signaled new mesocyclone development northeast of the tornado:

Here's the "rope-out" phase of this first tornado, followed by an image that shows where the 2nd primary tornado soon would form:

When the new tornado formed, a thin rope tornado was visible in its inflow stream (see 2nd photo below). Meanwhile, the primary tornado became large but was in poor contrast when viewed from the southeast:

Here's the "rope-out" phase of this 2nd primary tornado, which was on the ground around 15 minutes.  Notice a new mesocyclone again to its north or northeast, with a new tornado forming.  This new tornado was hard to see (again, poor contrast), did not appear to last that long, and seemed somewhat transitional in nature.  So I don't know whether it would be considered a "primary" tornado:

During this phase after the "transitional" tornado dissipated, it was hard to tell if the associated mesocyclone was splitting or just elongating eastward closer to Highway 283.  Here's a photo Shawna took:

As we drove closer, the lighting improved, and rapid rotation from this mesocyclone was evident, soon resulting in dust whirls and multiple vortices under a low ragged cloud base.  

After a couple rounds of "spinning and relaxing", a fully condensed new primary tornado developed under this mesocyclone, and lasted at least 10 minutes:

After a while. this new tornado began to narrow and elongate, signaling another "roping" phase as yet another new mesocyclone formed over Dodge City:

Fortunately, the elongating tornado moved west of Dodge, while the new mesocyclone dropped a new tornado (the last primary one) north of the town (notice Dodge City and the storm chaser/truck traffic in the foreground):

This last tornado appeared to be on the ground for 5-8 minutes or so, after which we lost sight of it as heavy rain from another storm overtook us from the south around 7:15 pm CDT:

So, based on  what we could see with this supercell, there were 4 primary tornadoes on the ground for more than 5-10 minutes each, which seems to agree generally with the map NWS Dodge City put on their web site:

We also saw one peripheral tornado in an inflow band, and one transitional tornado during a mesocyclone evolution phase that was difficult to assess, making 6 total for my conservative count.  I don't doubt that there were other brief peripheral or transitional tornadoes that one could count differently, but the 4 primary ones we saw appeared most significant.  Sadly, the tornado that passed just west of Dodge City damaged several homes and resulted in 2 injuries.   

This event was also notable for the circus of chasers, storm tours, and local traffic jamming up Highway 283 south of Dodge City.  One tour van nearly ran over my wife when they abruptly pulled off the highway, even though she was standing well off the road.  I'm pretty upset about that, and clearly the traffic issue continues to increase the danger of storm chasing.

If I get time in a few days, I'll post something about the meteorology of this severe event.

Jon Davies - 5/30/16

Sunday, May 1, 2016

Why no tornadoes? April 26, 2016 outflow boundary in northeast Kansas

I haven't done a blog post in a long long time.  But several people asked me why last Tuesday (April 26, 2016) wasn't a big tornado day in north & northeast Kansas as had been forecast.  So... it seemed a useful topic to start up posting again. 

With our many computer models, it's not hard to see potentially significant systems coming several days in advance, but whether they produce tornadoes or not often has much to do with features such as outflow boundaries and their orientation, which models certainly can't forecast very well.

Tuesday morning April 26 saw a strong area of thunderstorms move east-southeast across northeast Kansas and over into Missouri, producing a strong trailing boundary of cool outflow air (see satellite photo and surface map below).  

Strong surface-based instability (large CAPE) was present south of this boundary, but southeast winds producing wind shear supportive of potential tornadic supercells were largely limited to the area north of this boundary, separate from the warm sector instability (see SPC analyses of sfc-based CAPE & storm-relative helicity/SRH below at 20 UTC / 3 pm CDT). 

By 20 UTC, storms were forming along this outflow boundary, but because of the south-southwest to north-northeast mid-level flow aloft (see SPC 500 mb chart below), these storms moved immediately into the cooler surface air north of the outflow boundary.  

I adjusted the 21 UTC (4 pm CDT) Topeka RAP analysis profile (below), which was forecast too warm at the ground, by substituting the 21 UTC observed TOP temperature (69-70 F). The large green area (convective inhibition) on this profile confirmed the cool near-surface air north of the outflow boundary and the stable low-levels, which work against tornadoes, even though rotating storms (supercells) can still form in the overrunning instability and wind shear above the cool surface air.

Indeed, several supercells did develop north of the outflow boundary, although none could produce tornadoes in the cool surface air.  The radar panels below show one of these supercells (white arrow) that developed southwest of Topeka and moved north-northeast, prompting a radar-based tornado warning just northwest of Topeka shortly after 22 UTC (5 pm CDT).

The photos below show the cool air clouds north of the stalled outflow boundary, and the non-tornadic supercell as it passed west and northwest of Topeka within the cool surface air.

A somewhat similar situation (not shown) involving outflow and a stationary front over northeast Texas three days later on April 29 did generate a significant tornado at Lindale Texas, northwest of Tyler.  In that case, mid-level flow aloft was more west to east so that supercell storm motion was mostly parallel to the boundary, instead of perpendicular and up into the cool air, as in the Topeka April 26 case.

Outflow boundaries can help produce tornadoes, or they can hinder tornado production... it all depends on their orientation and strength relative to how storms move near them.

- Jon Davies 5/1/16

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 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