Friday, April 3, 2015

Moore damage survey of March 25, 2015

The Moore tornado of March 2015 provided a challenge to damage surveyors to derive an accurate rating.  Initially the NWS Norman office gave a preliminary rating of EF1 which led to some heartache by some of the media and yet allowed the survey teams to reassess the tornado strength.  Eventually the members of the four survey teams met to discuss whether or not the tornado should be upgraded.  There were several areas that were under consideration for an upgrade and the teams decided that the damage to several structures was enough to assign the tornado an EF2 rating and others that did not make the cut. This post provides some of the thoughts that went into deciding what to rate the tornado based on these structures.  Before going on, you may wish to visit the NWS Moore tornado page for detail on the tornado path and also this post about the meteorological aspects of the tornado.  I also highly recommend this blog entry by Robin Tanamachi for a well written story of what what it was like to be surveying this tornado.  This blog post is a more detailed perspective from someone who is a meteorologist trying to understand the point of view of an engineer and a forest ecologist when faced with damage to structures and trees.  I try my best but both the engineer and the ecologist have a much more in-depth understanding of the terms I attempt to use and the application to their fields.  You may find some edits to this post once they begin to read it.  :^)

The Moore tornado began at 2335 UTC on March 25 near Southwest 119th St. and May Ave. in southwest Oklahoma City and ending near Northeast 36th Ave and Indian Hills Road.   As the tornado matured it moved east and then took a turn to the southeast.  The track was surveyed by four teams:  The first covered the beginning quarter of the track (Chris Spannagle, Steve Mullens, Alyssa Bates and Matt Taraldsen), The second looking over the wide portion of the track just west of I-35 included Doug Speheger, Tiffany Meyer and Robin Tanamachi, The third covered the area from I-35 and east for three miles involved Dan Dawson, Robert Prentice and I, and then a team of one, Greg Stumpf, surveyed the final few miles of the track.
Figure 1.  A map of the Moore tornado of March 2015 including damage tracks and also a faded image of the rotation tracks where red indicates azimuthal vorticity of .01 /s or greater.   The three boxes represent areas of 

The first area of interest included the only areas of damage determined to be EF2.  These were in the vicinity of the Southgate elementary school area and then a half mile to the southeast.  Both team one and team 2 surveyed these areas but Robert Prentice and I did a more detailed survey of the Southgate elementary school (labeled '2' below).  The area of interest to me was the house with the highest degree of damage found in the entire tornado track and that is labeled '1' in figure 2.
Figure 2.  An intermediate zoomed view of the most intense portion of the tornado with EF scale contours and individual damage points where blue is EF0, green is EF1 and yellow, EF2.

The Southgate school area contained the most intense portion of the tornado with the maximum width and intensity.  Much of the tornado was dominated by a northwesterly inflow jet from the RFD with occasional corner flow vortices.  The strongest of these vortices hit just west of Southgate elementary and then to the southeast.  I’ll focus on the first one that included Southgate and a couple houses to the west (labeled 1 and 2 in figure 3).
Figure 3.  The highest zoomed view of the first area of interest including the EF2 house (1) and the Southgate elementary school (2a-c).  
 The house in the images below lost several walls once the roof was lifted away (figure 4).  According to the teams surveying this house, there were anchor bolts driven every 8’ to a depth of about 2” along the bottom sill plates into the foundation.  Otherwise there were shot nails driven into the foundation.  Not much is known about the roof-to-wall connections, however the house appears in Google’s street view product and some assessment can be made about the shape of the structure (figure 6).  While the house was embedded in shrubs a gable roof can be identified both on the west and south ends.   Since the debris in the picture facing NW appears to have blown eastward, the west gable was likely exposed to the strongest winds.  It is possible the weak links in the house were the gabled west side of the roof and the garage door seen in the second picture (figure 5).  The expected wind speed for collapsed exterior walls was 132 mph but team 2 lowered the wind speed down to the lower bound 113 mph.  Both lie within the EF2 rating.  The Cleveland County Assessors site indicates that the house was built in 1963. 

The next house to the north also lost its roof though it preserved all of its exterior walls.  The surveyors lowered the estimated wind speed to 107 mph, which is EF1, based on their similar appraisal of weaker than typical construction quality.
Not many other DIs exist in close proximity of these two houses, except for other upstream and downstream houses.  The trees in the pictures were located outside the core region of the tornado thus leaving only the telephone poles as potentially representative confirming damage indicators.  All of them were replaced after the tornado, however a piece of one lay against one of the collapsed walls in the first picture (figure 4).  Broken wooden poles also yields an EF2 rating with an expected wind of 118 mph.

Figure 4.  A photograph of the EF2 house with roof gone and some walls collapsed.   
Figure 5.  A photograph of the same house from its west side facing east.  The garage door blown inward was below a gabled roof end.  The house on the left also lost its entire roof but all walls remained standing.
Figure 6.  A Google street view picture of the house from the same view as the first image of the house above.  

 The Southgate elementary school, built in 1963, lost part of its roof on the southwest end of the building.  This image in figure 6 shows some of the debris that landed to the west of the school consisting of insulation boards and roof membrane.  

Figure 6.  The Southgate elementary school viewed from the west (labeled 2a in figure 3).
The southwest side of the school featured a peculiar roof uplift forming an arch, upon which the roof soffit was tilted into the vertical and may have subsequently acted as a vertical load support (figure 7).  Whether this support prevented the collapse of the roof deck is possible though unknown at this point.

Figure 7.  The school viewed from the southwest (labeled 2b in figure 3).
 The interior view of the roof uplift revealed in figure 8 shows an unreinforced CMU block wall.  In this hall the weak link was the grouting one course below what appears to be a very thin bond beam.  In the next room to the east the bond beam separated from the steel web joists.  The interior also shows the soffit that tilted vertically and helped to possibly keep the roof supported through its studs and plywood sheathing.  It’s not known here whether the uplift pressure was from  Bernoulli forces above the roof edge or interior pressure from breached windows in adjacent classrooms.  More likely a combination of the two forces pushed the roof upward.  The roof covering was still intact in this picture and shows insulation boards attached to the web joists.  I was surprised to see no metal roof decking.  Thus I considered this roof to be lower than expected quality for a wind speed estimate.

Figure 8.  An interior view of the uplifted roof over the entrance visible in figure 7.
Two rooms to the northwest a classroom lost all the roof decking, most likely contributing to the debris field to the west of the school.  No metal roof decking was visible in the debris field (figure 9).  Though here the bond beam appears to be a metal girder, stronger than the masonry bond beam further southeast, I considered this roof to be lower than expected quality here as well due to the lack of significant roof decking.  I rated this portion of the school as uplift of roof decking and significant loss of roof covering (>20%) with an expected wind speed of 100 mph.  I consequently lowered the wind speed to 95 mph.  This estimate still yields an EF1 rating.

Figure 9.   An interior view of a class room on the west side of the school.
A second area just east of I-35 had a single story house that lost the entire roof (figure 10).  The team in which I was on inspected this house to determine which side of the EF1/EF2 boundary the house should be rated.  Every house in the expected damage track was rated but only those appearing with colored triangular icons exhibited damage.  Thus the vortex was mostly too weak to cause damage except to a few houses where a brief damaging subvortex may have occurred. 

Figure 10.  An overhead map of the area of interest near Broadway Ave. just east of I-35.  The inset left points to the same area as the white outlined box in the main map.  The circle in the inset refers to the house in question.

This image in figure 11 shows the roof debris blown to the south side of the house consisting of composite shingles, 1by4” decking boards (likely tongue and groove) and 2X4” rafters spaced 24” apart.  Note the adjacent house to the east exhibited no apparent damage.   Adjacent houses to the west and north also showed no visible damage.

Figure 11.  A view of house labeled photo 2 in figure 10 facing northwest.   Figures 12 and 13 were taken at the label '1a and 1b' in the photograph. 
 This image on the east side of the house shows the part of the gable wall top plate and 2 nails (6d?) separated every 18” approximately (figure 12). 

Figure 12. A view of the top end of the collapsed gable roof including the gable wall top plate.  

The rest of the gable showed two nails between each rafter and the gable top plate approximately every 18”  (figure 13).  The gable fell nearly intact, however the orientation of this side was nearly parallel to the strongest wind, as determined by the direction of debris. It appeared though that the gable was poorly connected and exhibited no bracing.  While the lack of bracing appears to be common, the lack of a strong connection also appeared to be less than typical quality construction.

Figure 13.  A view of the rest of the gable.

Perhaps more significant than the low construction quality of the deroofed house was the lack of damage outside that caused by the debris.  These surrounding houses to the southwest showed little to no damage and even the fences remained standing outside the debris zone (figure 14).  The backyard shed was tipped over but it appeared to have no connection to the foundation other than gravity.  The light poles also were undisturbed except where the wires intercepted blown debris.  The only damage in the immediate vicinity occurred from impacts from debris.  As the debris from the roof and a car port blew to the southeast, it struck the fences and another house to the southeast resulting in the loss of exterior brick fa├žade and several windows (figure 15).  
Figure 14.  A view to the southeast from the house.  

Figure 15.  Two panoramas where the top one faces the house from the south end of its backyard.  The bottom panorama was taken from the backyard to the southeast of the house labeled '2' in figure 10.

Why did only this house suffer a loss of roof with the surrounding houses showing negligible damage?  One possibility is that this is the only house to have a car port in the vicinity (figure 16).  So there are two possibilities that affect our decision-making:  1)  The car port debris weakened the roof upon impact causing its failure. 2) A subvortex was small enough to only affect this house to the exclusion of all others.   Both possibilities yield a lower than expected wind speed because either collateral damage could’ve lifted off the roof at relatively low wind speeds or the duration of the subvortex over any spot would've led to a less than 3 seconds.   Consider that the vortex signature on the WSR-88D was moving between 40 and 45 mph and its diameter of maximum winds would be only 50 ft, the maximum winds would not have lasted the standard three seconds defined in the EF-scale.   This vortex would’ve needed to have spun up immediately northwest of the house because there was no visible damage to the houses across the street to the northwest.  However one house to the southeast (not the one with collateral damage) suffered loss of roof deck panels, suggesting the subvortex continued on to the east-southeast.

The degree of damage was labeled as large sections of roof removed, walls remain standing but the three second wind speed was lowered to roughly 105 mph or EF1.  The most likely scenario of what happened here is relatively weak connections between the top wall plate and the roof, along with possible impact from the car port allowed the subvortex to remove the roof from the house.
Figure 16.  A pre- and post-tornado view of the deroofed house as viewed from the northeast.  The pre-tornado view courtesy of Google Streetmaps.
 The final damage indicator that straddled the EF1/2 boundary was in east Moore where a 3600 sq ft house was directly hit by the core of the tornado (figure 17). 

Figure 17.  An overhead view of the final area under consideration, ShadyCreek St. just north of 19th in east Moore.  The inset shows the photo locations in subsequent figures including a wide panorama.
The house is a large single story wood framed structure with a hip roof design, brick and stone veneer and a composition shingle roof on OSB decking.  All the walls were constructed with 2X6” pine studs and roof rafters.  The owner built the house in 2014 and applied updated buildings codes that he promoted to the Moore City council following the May 20, 2013 EF5 tornado.  He mentioned that the house was built with anchor bolts and metal clips from the sill plate up to the top plate. 

The house experienced significant loss (>20%) of roofing above the complex roof-to-wall connections including the decking and numerous rafters (figure 18 and 19).  However there was no damage to windows or the garage doors on the north side of the house.  The adjacent garage shop west of the house lost shingles (DOD=1) and underlay on the south side while the neighboring house lost some shingles (DOD=1) on its west side (figure 18).

Figure 18.  A view of the three buildings including the house with the damaged roof.  Two insets indicate a pre- and post tornado view of the house.  

Figure 19.  A zoomed in view of the west side of the house.

 The tornado passed through the shelterbelt west of the house felling two large multiple trunk Elm trees with trunk diameters approaching 2’ (figure 20).  The smaller trees on either side were not affected thus supporting the premise that larger trees suffer disproportionately from severe winds even in an unfoliated state.   The tree damage indicators in the EF-scale were difficult to apply when vastly different tree response occurs within a just a few meters.  I used the standard wind speed of 100 mph based on either an uprooted or snapped tree trunk and assumed the tornado was of similar strength as at the house.  A narrow section of felled trees also could be seen in the woods opposite the field to the northwest.  The narrow width of felled trees strongly supports the idea of a narrow vortex progressing across the field and over the most affected house.  Due to its small diameter the buildings on either side escaped with relatively little damage.

Figure 20.  A panorama (labeled 'pano' in figure 17) including the houses and the shelter belt to the west.
 With the rafters clipped to the top plate and the lack of damage in the lower roof, why was the upper roof as damaged as it was?  A closer inspection of the roof near the ridge board revealed that the OSB decking was stapled to the rafters at irregular intervals (figure 21).  We could not measure the interval between staples but they were almost certainly spaced at greater than 6” intervals.  Since the building envelope was not breached it’s likely external pressure forcing overwhelmed the limited attachments of the roof decking.  The standard composition shingles offered no more than standard resistance to the wind.  This is below the quality of typical construction to give an expected wind speed and thus the wind speed estimate required to do this damage fell short of an EF2 rating.   Had the decking been clipped to the rafters this roof could’ve survived and EF2 intact and thus similar damage would’ve resulted in a much larger wind speed estimate.  Upon talking to the owner at the time, he admitted that he paid a lot for this flaw in his design.  If he used the same materials and techniques used to construct the porch overhang in framing the roof, he may have saved himself a lot of grief (see figure 22). 

Figure 21.  A zoomed view of the roof ridgeline  labeled '3,4' in figure 17 showing staples used to fasten OSB roof decking to the rafters.  

Figure 22.  A view of the east side of the house.

This survey though is about more than a single rating for the tornado.  With the advent of the Damage Assessment Toolkit (or DAT), we were able to create a high resolution survey from which the whole track could be contoured by EF scale rating.  The map that Doug Speheger of the NWS office in OUN, and others, created from this survey easily shows how small an area the EF2 winds occupied compared to the whole area that the tornado covered (figure 23).   By far the majority of the area covered by this tornado was only EF0 in strength and thus the energy that this tornado exacted upon the landscape was not as big as its EF2 rating suggests it may be.  

This is where high resolution surveys provide their biggest benefit.  Now we can see what fraction of the tornado path is occupied by winds of various strengths instead of making assumptions that has been standard practice based on a small sample of  well surveyed tornadoes.  Now the NWS has the opportunity to vastly increase that sample size and possibility to eliminate the need for more assumptions.  This information is more useful to NWS partners than many of us think.   Considering the users that include insurance industry, the Nuclear Regulatory Commission, risk analysts, FEMA, state and local governments and more and you may begin to see the value that comes from this level of detail in this NWS product.  It doesn't take a team of 12 people for every 12 miles to create them either.  It can be streamlined to be done quickly.  I'll reserve another post for that.  In the meantime, keep them coming!
Figure 23.  The map of the tornado path contoured by EF scale  published by NWS Norman.


To clarify, the media didn't force a reassessment of the tornado rating. Rather the initial rating of the EF1 allowed the NWS time to make a better assessment while still giving the public a preliminary assessment. 

Sunday, December 28, 2014

Could the Norman, ok snow of 27 Dec 2014 have been anticipated?

I'm sure the heavy snow that began early in the  morning of December 27, 2014 in Oklahoma was a surprise to many; an event which could've led to more significant impacts than what we saw given that it occurred only 2 days after Christmas .

 Was the snow event really as surprising as implied, and if not was there a way to effectively communicate a seemingly low probability event like this? In this day of exceptional numerical weather prediction, we shouldn't have seen a dry forecast just 12 hours before 3-6" of snow fell along the I44 corridor.  So the question is, was there no indication that a snow storm was on its way during the previous evening?
A scene typical of central Oklahoma roads.   Unknown source. 

Storm total snow amounts courtesy of NWS Norman. 

When the snow began to fall in thin bands as the radar image showed it appeared that an elevated frontal circulation was possibly involved. The 700 mb frontogenesis analysis in the SPC meso analysis plot helps support the idea, with the best values nicely lined up parallel to the snow bands observed by radar. This is important because the model guidance should have a similar signature in the forecasts. 

Frontogenesis at 700 mb in purple contours at 18 z from SPC.  

The NAM forecast model, however, didn't show much of any precipitation from the previous evenings run. What it did show in the Texas panhandle, however, appeared to be aligned in a similar direction as the frontal bands observed the next morning. But the NAM was as dry over central Oklahoma as the forecasts. 

The NAM 15 hr  forecast valid Dec 27 of 3 hour precipitation courtesy College of Dupage

The GFS evening model run, however, showed a slightly wetter pattern as a band of three hour precipitation accumulation appeared in roughly the same orientation and placement as was observed. The amounts were not quite up to the observed values but it's orientation gave a clue that it was on the right track that something may have fallen out of the frontal circulation aloft and that possibly an inch of snow may fall by late morning the next day.  The only problem was that this GFS forecast was available only after the evening news cycle was completed, thereby limiting its usefulness for planning in the evening before the event. Was there information in the guidance that could've been made a bit earlier?
Same as above except for the GFS. 

Well, possibly. In the afternoon before the snow day the short range ensemble forecast system, or SREF, showed that a several of its 15 runs forecast over one inch of snow in a corridor quite similar to the bands observed the next day. The probability of at least one inch of snow was only up to 20% in the college of du page model output but the SPC plume diagram valid for Norman showed that the several runs depicting the snow were very similar in timing and amounts. At least this output should give one pause that something may happen. 

The SREF probability of 12 hour snow exceeding 1" valid 18z Dec 27 courtesy of the College of Dupage.  

An SREF plume diagram of snow fall for Norman, OK from 21z Dec 26 courtesy of SPC. 

By 9:30 pm the evening before, three successive runs of the HRRR (high resolution rapid refresh) model were available that showed an axis of snowfall accumulation approaching or exceeding 1" right over the I44 corridor into the OKC metro area.  The hourly model runs allows its users to assess the consistency of its forecast. When three runs in a row showed a similar forecast then the likelihood of accumulating snow may not have been so improbable. 

The HRRR total snowfall at forecast hour 15 for the 23 z Dec 26 and 01 z Dec 27 runs courtesy of NOAA/GSD. 

So the big question of the evening was whether or not the guidance provided enough confidence to forecasters to go with some kind of winter weather warning.  In the NWS, forecasters are provided with a set of guidelines on when to issue winter storm watches, warnings and winter weather advisories. The NWS could've issued a winter storm watch, however they would need a 50% chance that winter precipitation would actually fall and accumulate to create hazardous travel conditions (see the directives at However we could debate for a long time whether or not there was a 50% chance based on the available guidance. One forecaster may consider that there needs to be a 50% chance that a winter storm warning criterion snowfall occur while another may not. I believe no one would argue that the chances of 4" or more accumulation was nowhere near that 50% value. Yet the directives suggest that a local forecast office has great latitude in determining the criteria for issuing a winter storm watch. Having snow falling enough to cover roads at rush hour would certainly be a good reason to consider sliding the threshold downward.  But this is a judgement call and the uncertainty in the guidance is enough that I can understand a forecaster decision not to issue a winter storm watch.  

No watch was issued for this event, but perhaps because a forecaster considered the chances of winter weather to be at 20 or 30%. With those low, but not negligible odds, What kind of message did a forecaster have available to advise the public?  A hazardous weather outlook could've been issued. However those kinds of products are usually reserved in the day 3-7 lead times. A special weather statement could've been issued since its format provides enough flexibility to provide a variety of information.  Perhaps then the statement could've been backed up by reposting to newer avenues of communication such as online briefings, social media and nwschat.  Typically these avenues are reserved for winter events with a higher confidence forecast. 

Communicating a heads-up about low probability events is commonplace in convectively induced severe weather events but not for winter weather situations. Yet in the plains states, and other places, high impact events are often dominated by mesoscale processes (eg. Frontal bands, cold frontal squall lines), as this event demonstrated.  These events are going to be more difficult to forecast, and therefore, lower confidence of occurring as anticipated for any one spot, much like summer convection. Thus the communication required to warn for the potential impacts have to be different than the synoptically dominated snow storms for which the traditional avenues of communication are intended.  The challenge is when and what to communicate with these lower probability but potentially significant events. 

Saturday, April 19, 2014

Learning moments from the May 2013 Oklahoma tornadoes

I put together a presentation for my Alma Mater, SUNY Oswego back in December of 2013 about what learning moments came to the foreground from the tornadoes earlier in the year during May.  These tornadoes differed from just about all other outbreaks in that the same metropolitan area was struck on multiple different days.  The Moore 2013 tornado, being the third violent tornado to strike that city in the past 15 years, exacerbated the sense of fear from these storms, and also set the stage for an unprecedented public reaction to yet another large tornado threatening the metro just days later.  The closest analog to this kind of severe weather would be the multiple tornado outbreaks of May 2003 from Missouri to Oklahoma.  What I present is somewhat biased in that it focuses on my worldview, however I've been influenced by many discussions about the May tornadoes and thus I've changed my view, consciously and otherwise.  Many of these learning moments have been repeated with earlier major tornadoes in other parts of the country, and even here in Oklahoma from years past.  Perhaps, however, with the tornadoes of 2013, and the heightened focus on the risk management of the residents in this state, this tornado outbreak helped focus these topics like a laser in our discussions.  I'll reflect some of these in this series of pictures with captions taken from my presentation.
Yes, central Oklahoma suffered in 2013. However, so many tornadoes in close proximity to a large meteorological center provides a great opportunity to learn from these disasters. Not everything learned is in this talk, but hopefully some essence of what is learned can be had from these pictures to follow.

This is an animated slide in the presentation highlighting the quality of forecasting has improved remarkably over the past years. When you see this level of risk where you live, take it very seriously.
The model guidance also is improving dramatically. Perhaps this forecast is a little too good to be true. That a 23 hour forecast from a convection allowing model can nail a supercell to within 3 mi of it actually occurring is incredible.
This is the storm that was forecast so well, I could've camped on Lake Thunderbird to wait for the tornado.  If only I could depend on that more than once in a full moon.

More typically convection allowing models yield usable forecasts with several hours to half a day lead time.  Ensemble model systems can be helpful in determining the mode of severe weather.
That kind of guidance is valuable in helping the SPC issue not just tornado vs. severe watches, but what level of confidence to apply to each type.  I put this slide in to show that not all tornado watches are equal.  There is a lot of information about the likelihood of weak and strong tornadoes posted on the SPC web page.  They were maxed out on the El Reno tornado day.
The NWS and the DOT worked together to make sure anyone passing under this, and other signs, knew of the impending severe weather.  This message wouldn't be here without the collaborative forecasting done between the SPC and the local forecast offices in addition to the major NWS stakeholders. Note that the sign focuses on expected time of highest threat.

The tweet has the same expected time of danger as the highway sign.  This kind of messaging consistency is highly desirable.

The NWS provided advice when watches were issued.

Note this advice strongly encouraged people to travel with a destination in mind well before the warnings came out.

And when the warning goes out, the NWS provided this advice.  There is nothing in the advice at this late hour that discusses driving somewhere.

What was the reaction on the El Reno day?  Not what was desired.

Thousands of people took flight.  Here are multiple reasons that resulted in this mass short-fused migration. I note the TV broadcasts were not solely at fault. It was also the heightened anxiety from the Moore tornado and the OKC culture, corrupted over years of fears that residents would not survive in their homes without going underground.
The panic was strong enough to overwhelm many driver's sense of responsible driving leading to this self-organized contraflow.  However, the word 'organized' may not be the best term to apply when the underlying forces are caused by panic.
Almost forgotten amongst the populace was the flash flooding as numerous storms trained over the metro area after the lead El Reno tornado producing storm.  The flooding potential was not a surprise, however.  Numerical model guidance and forecasters highlighted the potential for flood producing rains and a flash flood watch was issued.  In the Oklahoma culture, the tornado threat provokes images of fear leaving the flash flood threat in the dust of the collective conscience.

Significant casualties occurred as a result of people fleeing from the tornado threat and into flood zones.  Some people lost their lives when they hid in a drainage tunnel.  

What was the problem? It was the inconsistency of the messaging amongst members of the integrated warning team. This problem keeps being cited amongst various reports like the Joplin tornado report by the NIST or the NWS Service assessment from the 2011 tornadoes.  Of all the places where consistent messaging should be most desired, it should be in the Oklahoma City area.
The mass evacuation on May 31 was not solely the responsibility of the media's messaging.  The stage was already set by the sense of dread so dramatically acquired after the May 20 tornado hit Moore.  NWS service assessment findings indicated many of those that evacuated felt compelled to leave, and yet then regretted that decision.  Will that regret result in more appropriate reactions to a tornado warning in the future?  Perhaps, or perhaps not.

This is a complicated graphic but it's so revealing. Someone's risk is a function of his/her vulnerability and the intensity of the event that could potentially make him/her vulnerable.  Consider that someone is much more vulnerable at a camp site, or in a small boat vs. an office building or a large ship.  Certainly someone in a large building need not worry too much about a severe thunderstorm warning but someone in a tent should be understandably concerned.  People need to understand their own risk management. Not the NWS, nor anyone else can do it for them because they vary so much. Instead warnings are issued with single threshold that cuts across a wide spectrum of people's vulnerability.  They do the best they can but it won't be enough to account for everyone's vulnerability.  But technology can help.  Perhaps smartphone tools will come about to help interpret someone's risk management for them.  Some tools are already in development, as I understand now.

A big part of risk management is deciding what needs to be done with X amount of lead time, one of the major determinants of vulnerability.  When residents had plenty of time, a larger proportion of them decided to flee.  Others decided they had time to gather important belongings, and get more information.

Fleeing by vehicle during a warning may seem like good risk management but I doubt many people made any adjustments to their sense of allowable time when everyone wanted to flee.  I'm confident that panic resulted in many drivers once they felt like they were taking too much time relative to their perceived sense of acceptable lead time.  And they would be right should the storm have produced another large tornado in the metro.

Had the parent storm of the El Reno tornado decided to put down another one of those tornadoes, multiply this picture by 100s and that's what could've been a plausible scenario of poor risk management on a massive scale. This is an example of super high vulnerability.

This strategy of these postings at OU could help steer people's risk management in the right direction. Perhaps more of them would stay at home. Most would survive, as past experience of violent tornadoes striking urban areas show.  Only 0.6% of those struck by violent tornadic winds in homes didn't survive. But a higher percentage of people would be injured thanks to the quality of our housing.  And nobody tracks the consequences of those injuries.

High vulnerability lies in our collectively poor housing quality, maybe not as high as being in a vehicle but high nonetheless.

There are exceptions, such as new neighborhoods along the Gulf or East Coasts built to modern hurricane codes. These houses near Lady Lakes, FL performed so well that it was tough to rate the tornado. Typically houses with shingle loss and cars blown around would not be seen together for typical construction. These houses are tough.

Certainly shelters have been proven time and time again in OK with the onslaught of violent tornadoes in the past few years.  More and more shelters are being installed in central OK and they have a long proven track record of saving lives.  I heard over 200,000 of them have been installed in OK over the past few years.  This is the ultimate of 'lowering your vulnerability' act.

To help people manage their own risk, we need to give them better guidance. Thus our warning system needs to change.  Recall the single threshold and lead-time paradigm today in the NWS.  This will change.

Part of that change will come about with better input available for the NWS forecaster to make better decisions.

That's what the Hazardous Weather Testbed is all about.

The HWT allows forecasters to try out new technologies, give feedback, and improve the input.

Phased array radar is one of those new technologies that could revolutionize forecaster input.
Super-rapidly updating model guidance is another game changing input paradigm.  But the technology will not be ready for some years if forecasters want new model guidance every several minutes as input into short-term warning updates.

But such wonderful new technological input may seem lost when the warning output from the forecaster is 40 years old. We can do better.

Maybe we already are. On the El Reno day 2013, the NWS OUN office was putting out information by the minute, much more frequently than the 40 year old warning model. This output went out via multiple channels each day of severe weather.

In the future, warning output may allow warnings to follow storms. Thus no one place gets their lead-time shafted by discrete, static, polygon issuance. 
Then there's FACETS, a project at NSSL to take the output to the next step where gridded probabilistic guidance by hazard can help inform people while they manage their risk. It'll take a lot of work to realize what form this output will take. But whatever form it takes, certainly institutions responsible for moving large numbers of people (e.g., large outdoor venues and hospitals) could use this guidance to begin preparations well before any legacy warning gets issued.

Still, we go back to the quality of our housing. Risk management is a lot easier if our houses were built well enough to provide us some level of decent protection.  It's not just health but also we've got to consider mitigation of lost productivity due to loss of property.

It's major events like the Moore tornado 2013 that give us learning moments about how to build better.

We learn by doing surveys.  Aerial, even satellite imagery helps define areas of interest where we want to investigate further.  This Aster instrument showed dramatically lowered vegetation health (healthy is red) along the tornado track.  It even showed a kink in the damage path next to I-35 in Moore that was worth investigating some more.

Aerial and ground surveys help us assess the damage intensity and its spatial extent.

Our surveys were also assisted by radar data at first to help narrow down the damage swath. It was the PX1000 radar data run by the Advanced Radar Research Center that helped spot the small loop the tornado enacted near the Moore Medical Center.

Several teams rated 4000 damage indicators.  This segment was near the Plaza Towers  Elementary School that was destroyed by the tornado and where 7 students were lost.   This imagery is from the Google Crisis Response imagery.

We find housing flaws that should not have happened. All homes in the neighborhood built ~2000 had their foundations swept completely clean while the neighborhood east of the school withstood the tornado long enough to have most walls down but debris remaining.  How could an entire neighborhood, built in this day in age, perform worse than an older neighborhood? Home buyers need to become better customers and demand better from home builders. But it shouldn't stop there. Towns need to adopt better building codes, not after a disaster, but before they happen!

School building construction performed poorly from the tornado. We know why and what should be done to mitigate this kind of performance. It's only through good risk management that the teachers managed to save as many kids as they did. They only need build proper reinforced CMU walls and connections to roof and foundation to save the rest.

Many houses have no continuous load paths. This picture is a screaming example of what the lack of a continuous load path can do. Well, I guess someone sleeping in an upstairs bedroom would be OK in this picture but what a ride it would've been.

One could build a steel reinforced concrete dome house for the ultimate in tornado resistance.  But how many home buyers want to live in a home that looks like a space ship?
Yet the couple that were in the house at the time of the tornado were injured simply because they watched it come from the kitchen bar without taking further shelter in the bathroom.  All interior rooms were completely intact with no sign of penetration of debris or dust without the need of a storm shelter.

Well, we don't have to live in a space ship for added protection. It's simple to create a continuous load path in a house under construction. A $1000 worth of clips, J-bolts and metal straps, anchoring the roof all the way down to the foundation, is a lions share of what's needed.  The rest comes from fortifying garage doors, windows, and adding cross-bracing through proper sheathing.  None of this is rocket science and all of it is worth the price, especially when considering the costs of retrofitting a house after it's built.

The labor might be a bit more, but what home buyer would turn this down if they knew how easy it is to do? This could save on a lot of damage.

Look what strapping did for an apartment complex in Joplin.

This apartment complex was in EF 2 winds yet did not suffer the level of damage commensurate with such winds for apartments of just standard construction.

These houses also had a continuous load path with steel reinforced CMU walls and proper roof attachments. The only Achilles' heel for any of these buildings still are the windows.

This office building in Woodward, OK would've done okay if it weren't for the windows inflating the building and blowing off the roof.  Can more be done with windows?

This hospital had laminated glass on one floor and none of it broke in the Joplin tornado. It's more expensive, just like a storm shelter. But who in Moore would complain?

Part of building better is understanding how buildings perform in real tornadic winds. Guess what, tornadic winds don't follow straight lines.

We've got a lot of assumptions about how buildings perform. Do they all really respond to a 10 m 3 second wind gust? Is that really the wind in a tornado? Do winds in a tornado environment always decrease in strength toward ground level as so many 'experts' assume?

No! And in-situ measurements are showing it.  This profile was taken during the Goshen, WY tornado during VORTEX2.  The Tornado Intercept Vehicle sampled wind speeds at 3.5 m AGL (3 sec gust in red) considerably higher than the DOW radar beam at 30 m AGL (yellow).

A lot of different assumptions have to be made when the peak horizontal wind is at 3 m above ground vs 30 m or even 300 m. It's time to throw the old thinking out.

The forces upon buildings can be much stronger with a constant or stronger for a vertical profile of constant horizontal wind in a tornado environment than what conventional wisdom may have implied earlier with a typical profile where wind increases with height from 3 to 10 m and above.  For winds increasing in strength toward 3 m, the forces would be stronger yet than what this graph shows.  It also means that the winds sampled by mobile radar sampled somewhere above 10 m can be greatly underestimated.  And we have not even discussed strong vertical wind components near ground

Videos such as this one in Leighton, AL show compelling evidence that intense vertical winds begin below car top level.  Wind engineers now realize this is true. Horizontal winds don't just pick up cars with no initial sliding or rolling.

And they are doing something about it. This simulator in Iowa State already is providing wind engineers data about how much stronger tornado wind stresses are than winds from other storms.

Mobile radar is also providing some compelling evidence that tornadoes are stronger than the damage-based climatology suggests in areas where there's not much to damage.

Not all the time do winds increase going from 10 to 3m.  We still need a lot more data to determine what tornado behaviors are associated with a reverse wind profile, and also strong vertical flow near ground level observed when tornadoes exhibit strong corner flow.  This information is critical.  Assets like mobile radar and in-situ probes, whether by the TIV or by smaller probes, will need to sample tornado environments numerous times in order to acquire data from a variety of tornado behaviors in a variety of terrain.  I encourage even those chasers willing to put armored vehicles in harms way to go the extra inch it would take to outfit their vehicles with research quality, and well sited, anemometers.  The latter may sound controversial but if their bent on doing this, they could at least help provide the data to answer these questions.  After the money spent on armoring vehicles, adding a research quality anemometer should be pretty trivial.  Then we can produce more accurate models of building performance in tornado environments.  *

To recap, I put this talk out there to highlight some of the learning moments that struck a chord with me.  I believe that the quality of severe weather forecasts has gone up considerably to the point where societal and communication issues dominate in any disaster.  Getting people to react properly by learning good risk management is key.  We've only scratched the surface in this respect and we can do so much more.  I believe that any K-12 school curriculum should contain a required course on risk management, whether it's managing funds to managing safety.  Now that's not to say that forecast improvements will help.  They will.  They will help as long as the method of communication keeps up with the forecast capabilities so that they continue to be useful.

But in order to help the public, and officials, manage their risk, the research community needs to continue to help the NWS change its warning paradigm.  No longer should the NWS be the sole providers of warnings.  They should also be providers of warning guidance so that all users can create their own warnings based on their own vulnerability.  Fortunately the momentum behind the FACETS program holds promise because it has grabbed the attention of NWS and NOAA management.   Now it must grab the attention of other sectors, especially the private sector.  They are the ones that can provide a broad variety tools to help users manage their risk.

Finally, let's do something about the built environment.  I'm getting tired of seeing one FEMA/NIST/NSF report after another talking about the inferior quality of our housing construction.    Fortunately, after three violent tornadoes visiting the city of Moore, I hear that housing codes may be upgraded.  The same has happened in Joplin, MO after their tornado.  Now I only hope that one day a disaster isn't required for codes to be upgraded.  Can we actually be proactive?  Well, I'm not holding my breath.  Sometimes, most of the time, it takes a consumer to want a better built house, to want better from their home builders.  I don't know the answer to this except more vigorous education.  Grab them when they're young, before they fall into the trap of valuing more frivolous furnishings like granite countertops above those things that could save their lives (e.g., shelters, sprinklers, continuous load paths).  Yes, that's another call for education in the K-12 grades.

* I do not assume any responsibility for the risk chasers put upon themselves should they decide to transect tornadoes with their armored, or otherwise, vehicles.