I’m wiped…been tracking severe storms for 3 days straight…actually it started last week when I was here until 3AM on Tuesday with those overnight storms…but this is going to be abbreviated…

Storms fired up on the higher terrain of the Pikes Peak region around noon and continued southeast across the plains well into the evening. Look at all of the severe weather reports we got!:

Obviously the story of the day was the widespread hail and hail damage in Pueblo…it’ll be interesting to see what the dollar amount of the claims ends up being and if it sets a record. At one point during the 2pm hour we had three seperate supercells in/around/moving in to the Springs and Pueblo metro areas at the same time! That is a rare occurence indeed. We tracked a funnel cloud over Woodland Park live on the air with the Neighborhood Weather Network camera on Gold Hill, tracked the large hail swaths with Hail Vision in Pueblo, and had scud clouds over Colorado Springs that were being reported as funnels…

One of the interesting things about the hail today was the shapes of some of it. These stones from Joseph show what almost look like the balls from “the ball and chain” weapon of the dark ages. The spikes you see can be attributed to the rapid rate of freeze that the water underwent…an indication of how cold it was aloft and how fast the updraft carried these stones through and above the freezing line.

Late afternoon had 5 or 6 distinct supercells south of Highway 50, one of which produced this tornado outside of Pritchett a little before 5pm. It was on the ground for about 3 minutes and thankfully produced no reports of damage. Thanks to Laura Ming for sharing her photos with us! A little after 6pm, through about 6:30, several tornado reports from south of Limon in Lincoln County came in. On radar, this storm appeared most likely to produce straight-line wind near 70mph and there is some downed power lines and tree branches in this area, but it will be interesting to see if the NWS finds evidence of a tornado in this region when they conduct a damage survey on Thursday. Doesn’t really matter I guess, if its wind and causes damage, who cares if its rotating or straight-line?

This storm did produce a pretty significant outflow boundary that developed some new storms over Pueblo (photo below left) in the early evening and made for some nice shelf cloud looking shots, but you can also see a newly forming base on the right side of the picture. It looks somewhat similar to the storm over Avondale earlier in the day that had a ragged wall cloud underneath it. What a crazy day…I’m ready for quiet weather!

It’s likely that you’ve seen some of the commercials on another station over the last 5 or 6 months, and if you have, you know that a lot has been made about 5 minutes. A relatively short length of time, but in the case of a severe weather situation, it could seem like an eternity, especially if someone is witholding, or doesn’t have access to what could be some life saving information. I guess in that sense you’ve probably raised your eyebrows once or twice when you’ve seen the commercials as it has been made to appear that there is a big discrepancy in the weather information being delivered to television.

Whether it is a lack of understanding or a concious decision to mis-lead, I’ll leave that up to you. I’m going tell you what is really happening with the National Weather Service Radar (NEXRAD) when severe storms threaten our area. Storms exist in the atmosphere in 3 dimensions. They are so many miles wide, so many miles long and so many miles tall (think of it as the x,y and z axis from your high school geometry class). When thunderstorms are present, NEXRAD scans at many different angles to the horizon, or what we call “tilts”. The image below depicts how increasing angles of the radar beam can give a 3 dimensional picture of the atmosphere.

In severe weather, or scan mode 21 (below), NEXRAD sends out and receives radar signals at 9 different angles to the horizon. The scheme begins by doing a 360 degree scan at half a degree above the horizon, it then performs a 360 degree scan at 1.5 degrees above the horizon and repeats this process by ending with a 360 degree scan at 19.5 degrees above the horizon line. This produces a volumetric or 3D picture of the atmosphere in a process that takes 5 minutes to complete. Each of these tilts arrives independently in our Live HD Doppler as they occur, we just don’t typically show you these individual scans as storms start to not really look like storms at the higher tilts and the reflectivity doesn’t represent precipitation that is falling from the storm.

So why do we need all of these tilts? By scanning in 3 dimensions we are able to ascertain depth of rotation (knowing that a storm has a tight circulation from its base through a 20,000′ layer makes you more concerned about a potential tornado), hail core positions and height within an updraft before they fall out the storm, intense updraft and storm height (typically the higher the storm top the greater chance of severe weather occuring). In contrast, the image below shows how a television station owned radar operates. It only scans one level. Scanning like this gives us very little to no information about the severity and potentially life-threatening imapact a storm may have.

In the image on the right, a bounded weak echo region (BWER- depicted below right in what would be the space between the high heel and the rest of the shoe) will show a tornado’s location when a hook echo is present. Note the difference in seeing the entire storm structure in 3D versus one slice on the left. Just under the 13 in our logo, you can see an overshooting top, also an indication of enhanced storm strength. In the single slice, you have no idea that one is present.

In the image above,  our sister ABC station in Houston, TX uses 3D NEXRAD imagery to show the intensity of rain bands in Hurricane Dolly as it came on shore near Houston. Note under the abc13 logo how a band that looks pretty intense at the surface (typical radar view you see on TV looks intense), but the slice shows that precipitation isn’t as intense higher up, so rainfall rates are weakening within that band. Below, you see a 3D radar image that allows us to see the condensation funnel of an actual tornado that moved through Moore, OK in a significant tornado outbreak that occured on May 3rd, 1999. A 2D radar image at one tilt just doesn’t give us all of the information, storms don’t exist in 2D.

Do you want the whole story or just a slice of it? You decide.

Its been an active week or so in Colorado in terms of severe weather and it continued as many of you saw the storm going up from Colorado Springs on Monday during the noon hour. Several updrafts are visible on this image Marty grabbed from the Falcon NWN. The most mature updraft is on the right and the convective pushes get younger as you head to the west (left) in this picture. Note how crisp the clouds are, an indication of intense convection and updraft strength.

Underneath this updraft the storm was showing many features of being a supercell thunderstorm. A supercell storm consists of a rotating meso-cyclone (small scale area of low pressure) with separated updrafts and downdrafts that allow the storm to exist for usually several hours or more. Most of our severe weather, especially the strongest tornadoes (EF4-EF5), are produced by supercells. Some of the low storm structure taken in this photo by Leroy Mills as the storm was developing the tornado that destroyed several buildings to the west of Elbert include several inflow features (Beaver’s Tail and Feeder Band), the rain free base with a wall cloud hanging from it and a clear slot just to the left of the wall cloud. This feature is associated with the rear flank downdraft.

The rain cooled air in the rear flank downdraft (RFD) rotates around the backside of the storm and undercuts the warm and moist flow of air feeding in to the supercell. When the conditions are right, the RFD air is able to be ingested back up in to the rotating updraft of the storm and is a key component of tornado formation. Its important to note that not all RFDs will produce tornadoes, some will spill out away from the storm and choke off the updraft as it cuts off the inflow. Occasionally new updrafts will form downstream, but many times the RFD will weaken and kill the storm.

My twitter friend “KattinColorado” was driving from Ramah to east of Yoder this afternoon and caught a couple of cell phone pics that she nabbed and sent to me (thanks Kat!). She caught this funnel near Judge Orr Rd and Yoder Rd around 5pm. I’ve labeled the funnel and the dark area in the background on the right underneath the storm’s base which is the main downdraft of the storm, or the rain shaft. Rain cooled air within this downdraft is hitting the earth’s surface and then flowing away in all directions (like water being dumped out of a cup onto the kitchen table), including toward the camera. Occasionally when this occurs, small wisps of dust will be seen underneath the funnel, which can be mistaken for “debris” to the untrained eye, but the motion of the dust away from the funnel/storm, is a giveaway sign of outflow.

As annotated in the photo, the “outflow” is likely what’s causing the funnel to be almost parallel to the ground as its undercutting and pushing the funnel outward away from the rain shaft too. This happens alot in the high plains of Colorado when storms are outflow dominant as the storms today were. This means that once the updraft gets going, the downdrafts are stronger than the updraft as some of the rain evaporates and accelerates the downdraft toward the earth’s surface. This eventually kills the storms off as the updraft gets cut off from its inflow and the storms collapse. Several cells were warned for (Severe Thunderstorm Warning) by the National Weather Service today, only to be non-existent 25-30 minutes later. Tough to get tornadoes in that environment, but we do typically see many linear cloud features (also associated with thunderstorm outflow) like this second picture that Kat took of a shelf cloud. This second picture also makes the formation of a tornado pretty unlikely this afternoon.

I’ve found twitter to be a great resource (its like having an army of weather spotters across the viewing area) over the last couple months. If you’d like to follow me you can do so at twitter.com/STORMTRACKER_13

Below is the blog I posted one year ago…7 hours after the Windsor tornado occured. It was an amazing storm by Colorado standards..moving northwest and producing EF3 damage, the most expensive tornado in state history. Continued prayers for the families that lost loved ones and their homes, they continue to rebuild today.

WINDSOR TORNADO ANALYSIS - POSTED MAY 22nd 2008

At 11:54am a large tornado approached the town of Windsor, which is located in extreme western Weld County about 9 miles southeast of Fort Collins and 50 miles NNE of downtown Denver. At this time on the reflectivity image above, the storm displays a classic hook echo just south of the “Windsor” label. This is about the time the video was being shot by KUSA-TV in Denver that is circulating on all national news outlets this afternoon. One important note about this storm is that the core, or downdraft and significant rain and hail is located near I25, to the west of the updraft. Storms are not typically oriented in this fashion in Colorado, but the steering wind aloft was from SSE to NNW ahead of large area of low pressure approaching from the west.

In the image above, I’ve gone “inside” the storm to look at the velocity or wind flow field (enclosed by the black circle. Radar can only measure velocity along the radar beam, in effect only measuring if wind is moving toward or away from the radar and to what magnitude it is doing so. The data is from the Denver NEXRAD, located east of Denver at Front Range airport, on a line from the storm to just left of the bottom right corner of the screen and extended from there to the airport. This line is important because thats the axis we are able to measure windspeed on for this particular case. Note the green colors just to the southwest of the “Windsor” label, these colors indicate windflow TOWARD the radar site (this by the way is the rain cooled Rear Flank Downdraft), while just to the right of there, the red/magenta colors indicate flow AWAY from the radar (this is the area of inflow into the storm). These flows sitting right next to each other within the hook echo indicates via radar that a tornado may be present and obviously in this case we know it was.

Zooming in closer to the velocity data, I’m here measuring what we call gate-to-gate shear, or the velocity of adjacent data pixels. Notice that the green color is showing -30mph (or 30mph toward the radar) and the adjacent magenta pixel is measuring +74mph (or 74mph away from the radar). Add them up for a total shear of 105mph. At  this point the storm was approximately 55mph to the northeast of the radar and given the limitations to measure speed at this distance with a widening radar beam it is safe to assume that the windspeed within this tornado was greater than 105mph at this time.

It will be interesting to see what the Boulder NWS office determines this tornado to be on the Fujita scale and if there were multiple tornadoes that were produced by this storm, or if one tornado was on the ground from about Platteville through Milliken to Windsor. I’ll talk more about the Fujita (now the Enhanced Fujita scale) scale and how its used to determine tornado strength later tonight if I have time…or maybe tomorrow. Please feel free to post your comments or well wishes to the folks affected by this storm.

ENHANCED FUJITA  SCALE

This scale was updated last year as we’ve learned more about wind speed and the damage it causes and is now called the Enhanced Fujita scale, with tornadoes given a rating of EF0-EF5. The old scale was simply the Fujita scale with ratings of F0-F5. Its named after Dr. Ted Fujita who was a leading pioneer in many aspects of tornado research including some current theory of how they form and in terms of doing damage surveys. Damage surveys are done by the local National Weather Service office after a tornado is reported and is important because the Enhanced Fujita scale is a scale of damage, not a scale of wind speed. Through research however, we know that it takes a certain wind speed to do a certain type of damage so we can estimate the wind speed of a tornado fairly accurately.

The two images above lead me to believe at this time that the tornado will be rated an EF3 as the train was taken off the tracks and a significant portion of several well built homes were destroyed. However, the rating of a tornado is more complicated than finding the “worst” part and calling it an EF3 or whatever the case may be.

If indeed the tornado was on the ground the entire time from near Platteville around 11:27am to outside of Wellington an hour later (and some radar suggests it may have lifted at least once and a second tornado may have formed), I’m positive in saying that it wasn’t an EF3 the entire time. Tornadoes, a lot like the parent storm itself, will strengthen and weaken throughout its lifetime. So we may find that for portions of its journey northward it was EF0, EF1 and EF2 at different points. It will also be interesting to see if the NWS observers find any EF4 damage. We’ll also get confirmation through the NWS folks if it was one single tornado or several that did the much talked about damage that has dominated national news today.

Given the dangerous situation that occured at the Dallas Cowboys practice facility over the weekend, I thought it address the cause of it, a microburst. These are rain-cooled pockets of air underneath thunderstorms, that can produce tornado strentgh wind and, as seen in these images, can be quite destructive.

Due to our arid climate, the high plains of eastern Colorado (even some of the big mountain valleys) are very susceptible to thunderstorm downbursts as our air at the surface is usually pretty dry. As a result, rain falling from a thunderstorm will evaporate as it descends.

Evaporation (the conversion of liquid rain drops to gaseous water vapor) is a cooling process in the atmosphere and if enough of it occurs underneath a thunderstorm or in its rain shaft, a very dense  pocket of air will result (especially in relation to the relatively warmer air surrounding the storm).

Due to the effects of gravity, this dense air becomes “heavier” than the warmer air around it and rapidly accelerates to the surface. As it encounters the ground, it then acts like water coming out of a house and hitting the ground, it spreads out in all directions. Under the right conditions, this can cause wind gusts along the outflow front in the neigborhood of 100mph. Below is a video from the Tulsa airport from April 1st, 2006 when a strong microburst damaged 4 airplanes.

The National Weather Service survey from the Cowboys practice compound estimated the wind speeds at 70mph, obviously enough in this instance to do some damage. One of our own, Dan Cochell - Host of the Drive Home on KRDO NEWSRADIO, lost a brother to a microburst near Lamar when the wind flipped over their trailer home. His brother was standing in the door and the structure landed on him. They typically cause some minor damage, fences and trees down, etc., but when they are strong they can be as destructive as F1 and occasionally F2 tornadoes.

I’m slacker guy that hasn’t blogged in a while, I’ll blame it on an island vacation and then trying to get back into the swing of things. Several supercell thunderstorms developed in southwestern Kansas on Wednesday evening and produced several tornadoes. We should some pretty good video at 5pm today, shot just outside of Garden City, Kansas.

Thought it was a good opportunity to sharpen up the radar skills so I used X-Vision (think of it as x-ray for radar) and took some vertical cross-sections of the storms. The image on the left shows three distinct supercells to the south of Garden City and southwest of Dodge City, about 50 minutes after the middle cell produced the tornado outside of Garden City. You can see a well defined hook echo to the right of the fainl s in Ulysses and a V-Notch on the opposite side of the storm.

An X-Vision slice from the same time showed a decending reflectivity core (a little farther back than the slice I’m showing here) and a BWER (bounded weak echo region). The BWER is the area that is “missing”  precipitation on the SW flank of the storm, but surrounded by intense echo. If the shape of the storm in the slice is a woman’s high heel shoe. the BWER is the area between the 4″ heel and the rest of the shoe. This is in the hook echo and represents the location of the tornado that was reported outside of Plymell at the time this image was taken. Even though we don’t show X-Vision all that often for storms in southern Colorado on the air, this is the type of analysis we’re doing on storms when we aren’t on television! I was posting updates on twitter pretty extensively during this storm, you can follow me at www.twitter.com/STORMTRACKER_13

I don’t remember if it was in the half hour before the 5pm newscast today or during the 5 o’clock, but there was a storm in Custer/Huerfano County that had a severe thunderstorm warning on it and at one point I remember mentioning on air that “this storm is rotating and I’ll continue to track it closely here over the next 10 minutes” or something to that extent. The storm at this point had several features that made me make this statement. An inflow notch and a bit of a hook echo showed both storm organization and some rotation on reflectivity (I wish I would’ve captured an image). Also present on velocity was a well defined couplet, an area of wind moving away from the radar (this was the inflow region of the storm) and an area of wind moving toward the storm (this was at the rear and was the downdraft portion of the storm). As you can see above, I’m glad I mention on-air that the storm was rotating and (hindsight is always 20/20) a tornado warning probably should’ve been issued for the storm. One reason the NWS probably didn’t is that the storms were “pulsing” at this point. They were going up, briefly maturing and then collapsing within a 40 minute time frame. This funnel lasted around 5 minutes per the reports I received. Thanks to the Terry Mathews for sending the pictures!

The tornado that occured at 11 mile reservoir on Saturday has been well documented, but there were two more tornadoes that day. Tom Magnuson, the warning coordination meteorologist with the Pueblo office of the National Weather Service went up to Teller County and surveyed damage from two tornadoes (one was actually in northern Douglas County). Thankfully no one was injured, but some trees were snapped/uprooted and apparently it just missed a couple houses. You can read Tom’s write up here.

Another morning with low clouds and fog, but notable is how small an area was affected.  We had some good looks at the grunge via the STORMTRACKER 13 Neighborhood Weather Network this morning.  Fountain had it worst with visibility down to a couple hundred yards, we had some low cloud and briefly some fog/mist here at NewsChannel 13…

Pueblo was partly to mostly cloudy but the cloud decks remained off of the ground, but the final image taken from US 24 and Peterson Road at about the same time shows no sign really of the low clouds we had here over downtown Colorado Springs.  If you look closely you’ll see the milky white haze near the ground representing where the low clouds and fog are, and how small an area they are covering.  It is not uncommon for areas of cool air and/or low level moisture to drain down the same channels that water does, in this case Fountain Creek into the Arkansas River which of course is where we’ve had the murky conditions…

Yesterday was a bit active on the severe weather front.  This photo from near Ramah shows what we call a “landspout” tornado which is jargon for a tornado produced from a storm that is not supercellular (storm lacking deep, strong rotation).  Non-supercellular tornadoes (”landspouts”) tend to be brief and weak, but they can still cause damage, thankfully this one did not.  Thanks to viewer Denise Ferris for sending us this photo!

Viewer Jan Gregg-Kelm has help from Mother Nature all around, the view, setting, rainbow, contrast, thanks for sharing Jan!