Radar Imagery Associated with the Indiana State Fair Stage Collapse

The purpose of this post is to show you some of the radar images associated with a line of thunderstorms that caused the tragic stage collapse yesterday evening at the Indiana State Fair.  For more specific details on the event itself, as well as my thoughts on how this tragedy could have potentially been avoided, please see my earlier post.





The first image was taken at 8:35 PM EDT by the National Weather Service (NWS) Radar in Indianapolis.  This was about 4 minutes before the official NWS warning was issued:

I have put a red dot on this (and subsequent) images showing the location of the Indiana State Fairgrounds.  On this first image I have also circled it in yellow (look near the center of the image under the word "Rocky".

The white arrows on the above image note the location of a "fineline", the thin blue line that you see (dotted in some areas, more solid in others) out ahead of the line of thunderstorms that were advancing toward the East at 25-30 mph.  A fineline is a radar signature that denotes strong, gusty winds (also known as a "gust front") blowing out ahead of a line of storms.  In this particular case, the gust front was approximately 5-7 miles out ahead of the line of storms on the Northern end (which is the portion that would have affected the Fairgrounds).

By the 8:44 PM image (below), the gust front was about 4 miles West of the Fairgrounds and continuing Eastward:

In just that 9 minute period of time, you can see that the fineline/gust front signature on the radar has advanced even further ahead of the thunderstorm line to the West of the Fairgrounds - a sign that the winds were growing stronger and advancing further East of the thunderstorm line at an even faster rate.

By the 8:53 PM image, the gust front was on top of the Fairgrounds, with the radar signature having advanced just to the East of that location: 

As I pointed out in my original post, a trained professional would have recognized the fineline/gust front signature on radar, as well as its Eastward acceleration, and the obvious danger that it posed to the Fairgrounds.  

The viewing of a radar image on a smartphone by a non-trained individual (see my original post for those details) simply doesn't get the job done, and carries potentially disastrous consequences as we've unfortunately seen in this case....

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Very Large Hail East of New York City Today...

The above video was captured about an hour ago by a resident of New Hyde Park, NY, on Long Island, about 25 miles East of New York City. As you can see, hailstones of quarter to tennis ball size can be seen plopping in the pool and on the porch!

The radar image below shows the storm responsible for the very large hail earlier in New Hyde Park.  It is currently drifting slowly toward the Southeast:

The left half of the image shows the radar in "reflectivity" mode (i.e., rain, hail, etc.), while the right half shows the radar's VIL "vertically integrated liquid" mode.  As a general rule, the higher the VIL value (i.e. the white and grey colors on the image), the larger the hail.

Jump back to 4:20 PM EDT, which is about the time most of the large hail was falling in New Hyde Park, and you can see what the VIL image looked like at that time:

The green triangle just to the right of "New Hyde Park" on the image is where the radar was estimating 2.5 inch diameter hail was falling at the time.  Turns out the radar was "right on" in this case....

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A Tornado Warning in a Very "Unlikely" Place...

A Tornado Warning was recently issued on this storm between Houlton and Presque Isle, Maine. Yes, I said Maine. No ground-truth reports yet, and the wind velocity (wind speed & direction)  mode of the radar (see below) tends to indicate strong, gusty winds blowing out of the storm rather than pronounced rotation.  With that said, brief (and generally weak) tornadoes sometimes spin-up on the leading edge of such storms...

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Radar Imagery Associated with the Joplin Tornado of 5-22-11

This article will present a series of radar images depicting the supercell thunderstorm that produced the devastating EF-5 tornado in Joplin, MO on May 22, 2011.  The vantage point is from the NWS radar near Springfield, MO (about 55 miles to the East/Northeast).





First, a little radar refresher course for our newest readers.  I'll be showing two types of radar images:  Base Reflectivity and Storm Relative Velocity.  Base Reflectivity images show the radar's depiction of rain, hail (and as you'll see in some images, debris), being reflected back to the radar.  Storm Relative Velocity images show the wind speed and direction within the thunderstorm, as estimated by the radar.





When examining the storm relative velocity (SRV) images, keep in mind that the red colors depict wind motion away from the radar site, while the green colors depict wind motion toward the radar site.  In this case, the radar site is located off of the images, toward the East/Northeast (or upper right).





Now that we have the basics out of the way...lets take a look at the images from that fateful day back in May...





The first series are Base Reflectivity images, starting at 5:34 PM CDT and ending at 5:58 PM CDT.  The interval between each is about 5 minutes.  Joplin is located just to the right of the center of each image (click to enlarge):

Reflectivity image at 5:34 PM CDT

Reflectivity image at 5:39 PM CDT

Reflectivity image at 5:43 PM CDT

Reflectivity image at 5:48 PM CDT

Reflectivity image at 5:53 PM CDT

Reflectivity image at 5:58 PM CDT

As you can see, a pronounced "debris ball" becomes visible at about 5:43 PM CDT, as debris is being lifted aloft and carried away by the tornadic storm.  I've annotated the debris ball with a white circle in the images below:

Reflectivity image with debris ball at 5:43 PM CDT

Reflectivity image with debris ball at 5:48 PM CDT

Reflectivity image with debris ball at 5:53 PM CDT

The next series of images shows the same radar in Storm Relative Velocity (SRV) mode, at the same times as the above reflectivity images:

SRV image at 5:34 PM CDT

SRV image at 5:39 PM CDT

SRV image at 5:43 PM CDT

SRV image at 5:48 PM CDT

SRV image at 5:53 PM CDT

SRV image at 5:58 PM CDT

As you can see, the tornadic signature was initially moving East/Northeast and then turned more toward the East and then Southeast after crossing Highway 71 on the East side of Joplin.  This corresponds well with the ground-truth damage survey as completed by the NWS:

Values inside the triangles correspond to EF intensity

I'll explore the change in track in greater detail in a later post dealing with the damage assessment as related to radar and satellite imagery.

Remember earlier when I pointed out that greens show the radar's estimation of wind blowing toward the radar site and reds show the wind blowing away from the radar?  This is where we put that knowledge to use.  I have taken the same SRV image shown above from 5:43pm and circled (in white) the rotation couplet as indicated by the radar in the image below:

Rotational couplet on radar peaked at 5:43pm CDT

At this point, the radar was estimating that wind speeds at the center of the white circled area were approximately 141 mph toward the radar and 69 mph away from the radar, for a total "shear" (or opposing wind motion) value of 210 mph at that point.  It's important to keep in mind that the thunderstorm and associated tornado were about 50-55 miles from the radar site near Springfield at this point.  At that distance, the radar was scanning the storm at a level between 4,000 and 4,500 feet above ground on the above image.  Even with that in mind, the total wind motion value of 210 mph as estimated by the radar corresponds quite well to the ground-based storm survey which indicated damage consistent with winds in excess of 200 mph in this region.

You may have also noticed the small red "plus sign" and the small yellow dot located near Joplin on the above images.  The red plus sign corresponds to the location of Sam's house, and the yellow dot corresponds to the location of Joplin High School.  I thought it would be interesting to zoom-in at street level on a couple of selected radar images and take a look at how the radar signatures correspond with those hard-hit locations.

First, the Storm Relative Velocity (SRV) image at 5:39pm CDT, which shows the tornadic circulation growing stronger as it approaches Sam's neighborhood and the Main Street corridor.  At this point, the radar was estimating 148 mph of total wind motion near the circulation center:

Zoomed-in SRV image at 5:39pm CDT with rotation noted

By 5:43pm CDT, just 5 minutes later, a pronounced debris signature was noted on the reflectivity image, extending just over 1 mile across, as debris was being lifted and carried aloft by the tornadic thunderstorm:

At the same time, the corresponding SRV image estimated 210 mph of wind motion in association with the circulation center, just to the East of the High School:

The satellite image below is zoomed-in on the same general area as shown above.  You can see the level of destruction that took place along the path of the strong circulation center.  The brown "swath" of damage in the satellite photo is about 1 mile wide on average, which also correlates quite well to the radar signatures above.  I've added notations of the High School and Sam's House as further points of reference: (click to enlarge):

I'll be taking a much closer look at the damage as detailed by satellite and other imagery (photos, video, etc.) in an upcoming post on the damage assessment.  I also plan to match-up some additional close-in radar images to correlate with the damage imagery as well.

For more on the Joplin tornado event, click here to return to the table of contents post, which contains a chronological listing of all related posts, and will be updated with new links as additional posts are made.

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New Technology Coming "Soon" to a Radar Site Near You...

The first major upgrade to the National Weather Service's WSR-88D radar network in over 20 years is getting underway across the country. The latest technology being rolled out is called "Dual Polarization".





"What the heck is that???" and perhaps more importantly, "what's in it for me???" - you ask?





In a nutshell, the conventional WSR-88D radar sends out a single pulse of radar energy into a storm, which captures a generally horizontal snapshot of raindrops, hailstones, snow flakes, etc. (as shown on the left half of the illustration below): 

The right half of the same illustration shows what Dual Polarization technology will do.  The radar will not only send out a horizontal pulse of energy (red) but also a vertical pulse (blue), which will give us a far greater depiction of the size, shape and density of raindrops, hailstones, snow flakes and other targets.

Dual Polarization (also known as Dual-Pol for short) radar technology has been installed and tested for a number of years at the NSSL in Norman, OK.  Within the last few months the rollout to operational NWS radar sites has begun.  The first site to be installed was at Vance AFB, OK, followed by Phoenix, AZ and Morehead City, NC.  As this is being written, Dual-Pol is currently being installed at radar sites near Pittsburgh, PA and Wichita, KS.  A complete schedule of the rollout, which will continue into early 2013, is located here.  Each installation takes about 2 weeks to complete, during which time the radar unit will be out of service to allow for both the upgrade and training at the local NWS office.

Now that we know what Dual-Pol is, what will it do for us?  Perhaps the greatest initial impact will come in the form of vastly improved precipitation estimates.  With the current WSR-88D technology, a thunderstorm must be in existence for about 1 hour before the radar is able to estimate how much rain is being produced.  With Dual-Pol technology, we'll receive a nearly instantaneous read on rainfall rates.  This will obviously have enormous potential not only in regard to flash flooding & other severe rainfall situations, but also in dealing with snowfall, ice accumulations, etc.

Dual-Pol rainfall estimate (left) vs. WSR-88D estimate (right)

Current technology on the WSR-88D sometimes makes it difficult for the radar to differentiate between hailstones and raindrops, particularly at greater distances from the radar site.  As a result, the 88D often over estimates the rainfall rate with severe storms (mis-identifying hail as heavy rain).  The Dual-Pol technology will make the estimates more accurate in these situations (see the above image for just one example).

Dual-Pol technology will also aid in the tornado warning process.  Right now, it takes a fairly large debris field (which usually means a fairly large tornado) to produce a debris signature on the WSR-88D.  A Tornadic Debris Signature (or TDS) can be detected by Dual-Pol radar in association with a much smaller debris field (which means a smaller tornado).  Please note that I am talking about debris being detected by the radar here, not rotation.  In the database that was used to develop some of the algorithms for the new Dual-Pol radar system, debris signatures were observed with tornadoes as weak as EF2 intensity (winds of 111-135 mph).  Today we would normally only see a debris signature on the WSR-88D in association with a tornado of high-end EF3 to EF4 intensity or greater (roughly 150+ mph surface wind speeds). 

The above image was taken from the Dual-Pol radar at the NSSL radar testbed in Norman, OK.  The white and pink colorations within the white circled area on the image shows where the Dual-Pol is detecting tornadic debris.  This debris field was not as easily identified on conventional radar.   Of course, you must also keep in mind that the tornado, regardless of strength, would have to be in an area where debris could be picked up before the radar would be able to see it.

Dual-Pol technology is likely to be of particular help in the tornado warning process in 2 specific areas:  (1).  when the circulation is rain wrapped and not easily visible by storm spotters and (2).  when the circulation is occurring at night and not easily visible to storm spotters.

The system will also be a big help with non-precipitation events as well.  Because it takes a more detailed "slice" through the atmosphere, Dual-Pol technology will be able to forewarn of local hazards near the radar site, like dust storms for example.  Below is an image taken by the Dual-Pol radar near Phoenix, Arizona this past Tuesday, July 5th:

The red dashed line notes the leading edge of a wall of dust that was advancing toward the city from the South.  Here is what that advancing dust cloud looked like outside the National Weather Service office:

The enhanced scanning of the atmosphere very near the earth's surface by the Dual-Pol radar will allow it to detect very small particles, like the dust particles above, as well as insects, birds, etc., close to the radar site.  The WSR-88D is already able to do this to some extent, but the resolution and detail of such scans will be even greater with the new Dual-Pol technology.

Now that we have a few Dual-Pol radars online and others being added about every 2 weeks, I'll be posting some images of the new technology in action, and comparing it to the old where possible.  Stay tuned!

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Watch for the Bows, and I Don't Mean Pretty Red or Pink Ones...

When thunderstorms form into a solid line, the potential for wind damage often becomes rather widespread.  A tell-tale sign of likely damaging winds on radar is the "bow echo" or a bowing segment that occurs within the line.  

The image above was just taken from the Vance AFB radar near Jet, OK.  I have placed 4 white arrows on the image, identifying bowing segments within the overall line of storms (click to enlarge).  Wind gusts of 70 mph were recently reported near the Northern-most three arrows.

As the evening progresses, watch for similar bowing segments within the line of storms.  That is almost always where the strongest winds are taking place.

P.S.:  Special note to 'The Planet Pink', one of my most loyal blog followers - I apologize for the derogatory reference to red & pink bows in the title of this post....but it seemed to fit the situation...

Severe Weather Update - Nebraska

**Updated to include tornado photo mid-way down through post:

A complex scenario continues to unfold across southcentral Nebraska.  Above is the latest radar image from Hastings, showing several supercells that are all merging in a region from Southeast of Grand Island to Loup City and points just to the West.

The smaller white circle shows the current location of the circulation that produced a damaging tornado in the Miller and Elm Creek areas during the last hour.  The larger circle shows the strongest rotation currently indicated on a storm located near to the South of Loup City.  This activity is generally moving Northward at 25-30 mph.  Loup City and Ashton are both in the path of the strongest circulation indicated by radar at this time.  Seek shelter immediately if you live in the path of these storms.

The storms over toward Grand Island and points Southeast are very severe, with large hail & wind damage likely.  They could also produce a tornado at any time, so please take tornado precautions if you live near these storms as well.  The storm near Stockham to Aurora is starting to show signs of organized rotation and will move North/Northeastward at 25 mph.  Henderson, Hampton and Bradshaw are in the path of the most dangerous part of this storm.

**Updated with photo at 6:10 PM CDT:

Below is a picture taken of a tornado on the ground between Hampton and Bradshaw, to the West of York, shortly after this post was originally made:

Photo by Todd Rector, as uploaded via Twitter

**Continuation of the original post:

Below is a radar image taken at 4:12 PM CDT, when the damage was being caused in the Miller and Elm Creek areas.   You can see the pronounced hook echo with a debris ball (as noted by the white circled area), showing where debris was being lifted up and carried by the tornado at that time:

Any one of the storms currently over southcentral Nebraska could organize and produce a similarly damaging tornado at any time, so please seek immediate shelter if you're in the path of the aforementioned storms.

Five Supercells - Five Tornado Warnings - One Radar Image...

You're looking at the latest radar image from the Goodland, KS radar (click to enlarge).  You can see 5 supercell thunderstorms on this single radar image, each of which has a strong radar indication of a tornado.  Tornado Warnings are in effect for each of the areas within the purple polygons.  Average storm movement is East at 30 mph.

Numerous reports of funnel clouds and tornadoes have been received from these storms this evening.  Very large hail and damaging winds are also possible with this activity.