The biggest threat with storms this evening was lightning. From about 4:30pm to 5:30pm there were more than 900 lightning strikes in the Pikes Peak Region. Lightning is the deadliest weather phenomena in the United States. So far in 2009, 4 people have been killed by lightning. In 2008, 28 people died due to lightning strikes. If you are outside during a thunderstorm, remember the “30/30″ rule for lightning safety. If you hear thunder within 30 seconds of the lightning flash, you need to take cover. And then wait at least 30 minutes after the last lightning flash or thunder in order to resume normal activity.

We had some storms today that put down some heavy rain. Storms in northern Lincoln County produced rainfall totals of over 3 inches according to our Rain Vision, along with hail around an inch in diameter. Other storms led to rainfall totals of around an inch in other spots across southern Colorado.

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.

As the temperature goes up, so does the potential for getting sunburnt.  Did you know that one in five people will get skin cancer, often from the sun’s rays?  The good news is that skin cancer is preventable. Viewer Tip: The Friday before Memorial Day (May 22) is Don’t Fry Day.

It’s going to be close, but we could see some record breaking temperatures this week.  For example, we shouldn’t break the record Monday in Colorado Springs with a record high of 91 set in 1996.  But Tuesday will be a possibilty with the record high of 86 set last year (2008)!  We are forecasting temperatures to hit the mid 80s in the Springs Monday through Wednesday and in the low to mid 90s in Pueblo.

After a chilly start to the weekend, we’ve got some great weather to finish things up today. Highs will reach the 70s and 80s over the plains as a ridge of high pressure builds into the region. The picture below shows that ridge bringing even warmer air our way Monday afternoon with highs into the 80s and 90s across the plains. Denver’s record high temperature (93) will be threatened tomorrow with a possibility of a new record high for Colorado Springs (86) on Tuesday.

Pictures do the talking…

We did have enough moisture for a few cumulus clouds and even a bit of virga, long since gone…

The clouds rolled in this evening after a nice break of sunshine this afternoon! Low clouds and fog will develop overnight, but don’t let it fool you! It’s still going to be a beautiful day Monday! You might want to leave yourself a little extra time in the morning in case there is some low visibility on your commute in the morning!

Happy Mothers’ Day! We certainly woke up to a wide range of conditions this Mothers’ Day. Folks across the Pikes Peak region had some clouds while others across the southern portions of the state had some sunshine. Take a look…

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.