Straight line wind, microburst, or F0. How to figure out

Scott Freeman

Last night there was a svere storm that came thru our . There was wind damage done up the road about 2 miles. But the field of damage was very odd
The Damage field width was about 5 yards in width. and in length of 3/4 of a mile or so. But the damage was intermittant. At the start of the damage area ther was the tops of a couple of trees torn out. Then it missed several more trees for about 500 feet. then there was a street light taken down and another couple of trees that again had their tops taken down. After that there was nothing else for about 1500 feet, then it hit 2 oak trees that was at least 120 years old. It took bot of them down. The oaks represented the end of the damage path . The path that was made was made in a south west to north east direction. The trees fell parallel but one was 10 degrees off or so from the other.
At first i would think that it was straight line wind. But I have never seen or heard of straight line winds that was finicky with what they knocked of. Take the top ot of one tree, and then another that was 15 feet from it, it doesnt even touch it. To me it like something like a F0 that skipped the distance and when it knocked the oaks it might have just went up for good. Also if it was straight line or a mico burst i would think it would be a straight line of un interrupted damage, but it was not.
Based of what you have seen with damage in the past, can anyone speculate based off the description I gave...thanks in advance.
 
my suggestion would be to report the damage path to the local NWS, and see if they can get someone to come out and review it. Every office needs to have a few tornados on their docket.
 
A weak tornado can rarely be differentiated from straightline winds... The trees don't show convergence because the winds on the left side of the tor (going against storm motion) aren't enough to cause damage.

Look for things like individual tree branches and trace them back to likely source. Mud or debris on three sides of a structure. But without video you're likely to have a difficult time proving TOR.

"Also if it was straight line or a mico burst i would think it would be a straight line of un interrupted damage"

No correlation.

- Rob
 
I contacted my local NWS this morning, hopefully they will get out there investigate the damage. If they let me know I will update.
 
That hapened here in Parker once a couple years ago...in a garden a few stalks of corn were down, then half block away a couple of large limbs, and a couple more blocks away a large tree, couple more some lines...etc. The final determination was a microburst just on the edge of town, but I have no idea how they got that if all debris was in one direction.
 
" have no idea how they got that if all debris was in one direction"

There's no way to go weak Tor vs Straightline so we say straight line unless evidence or video shows Tor.
 
There's no way to go weak Tor vs Straightline so we say straight line unless evidence or video shows Tor.
Click to expand...

But it wasn't straightline, it was a microburst according to them...but there was no other damage in the county...nothing a few miles away going the opposite direction of where th emicroburst came from, since i'd think that damage would be outward in a circle from the "impact" point...
 
But it wasn't straightline, it was a microburst according to them...but there was no other damage in the county...nothing a few miles away going the opposite direction of where th emicroburst came from, since i'd think that damage would be outward in a circle from the "impact" point...
Click to expand...

"Straight line winds" is a generic term for all non-tornadic winds, including microbursts, derechos, etc.

The final determination was a microburst just on the edge of town, but I have no idea how they got that if all debris was in one direction.
Click to expand...

Since it impacted on the edge of town, would there have been anything to damage on the other side of the microburst's impact?
 
"since i'd think that damage would be outward in a circle from the "impact" point..."

Not unless you had a staionary storm... I can't imagine too many times that would be the case. Downburst winds spread out along the path of the storm.

- Rob
 
Twisted trees has NOTHING to do with tor vs straight... A straightline wind can easily twist a tree!

- Rob
 
Not unless you had a staionary storm...
- Rob
Click to expand...

While I understand what you mean, to avoid confusion for those less familiar, it is really only true for a storm without any wind motion through the depth of the atmosphere. In that case, then a negatively buoyant pocket of air would sink straight down and splash to the ground in a symmetric ring. A storm would certainly be stationary in this environment. Instead, thunderstorms often exist in environments where there is some mean wind direction, and often some degree of shear (change in wind speed/direction with height). You can have situations where a storm is stationary, but there is shear and mean winds, yet a downburst would not be symmetric in this case, as the raindrops (or simpy pool of cold air) above the ground would be in a region where the winds are not stationary, and this momentum is passed to the raindrops/cold air pocket, which then falls to the ground taking some of this momentum with them/it. As such, when the cold air splashes to the ground, the horizontal expansion of the ring of air is no longer symmetric - winds are much faster on the side of the expanding ring in the direction of horizontal motion of the cold air pocket. For example, think of throwing a water balloon at the ground a ways in front of you. Most of the water splashes away from you in the direction you threw the balloon, not so much splashes back towards you. In this way, most of the severe wind damage with a microburst is directed in the direction of the horizontal momentum of the downburst.

Hope this helps,
Glen
 
Last night there was a svere storm that came thru our . There was wind damage done up the road about 2 miles. But the field of damage was very odd
The Damage field width was about 5 yards in width. and in length of 3/4 of a mile or so. But the damage was intermittant. At the start of the damage area ther was the tops of a couple of trees torn out. Then it missed several more trees for about 500 feet. then there was a street light taken down and another couple of trees that again had their tops taken down. After that there was nothing else for about 1500 feet, then it hit 2 oak trees that was at least 120 years old. It took bot of them down. The oaks represented the end of the damage path . The path that was made was made in a south west to north east direction. The trees fell parallel but one was 10 degrees off or so from the other.
At first i would think that it was straight line wind. But I have never seen or heard of straight line winds that was finicky with what they knocked of. Take the top ot of one tree, and then another that was 15 feet from it, it doesnt even touch it. To me it like something like a F0 that skipped the distance and when it knocked the oaks it might have just went up for good. Also if it was straight line or a mico burst i would think it would be a straight line of un interrupted damage, but it was not.
Based of what you have seen with damage in the past, can anyone speculate based off the description I gave...thanks in advance.
Click to expand...

Microbursts can be small and very intense, and I believe there can be sudden changes in wind direction (depending on you location relative to the center of the burst).

I had an experience with a microburst back in December of '98 or '99, that many probably could have believe to be a tornado. A strong front blew through around 12AM (and temps were in the 40's) with a narrow line of convection along it. This was enough to bring down the 50KNTS in the first 1000ft of the atmosphere. Spotters reported 50-70MPH winds with this squall line. I was expecting a brief gust to 50MPH and some rain, but what I got was a treat. I heard what seemed to be an airplane getting louder and louder (as the roar got louder, people in the neighborhood were actually turning on their lights and looking outside)... A few seconds later, winds began gusting very hard (I had gone into the house at this time). I could hear the roar getting louder, with debris hitting the house. As I looked out the window, the pines in the front yard were bending to their limits (thought they were done for). After the excitement, I decided to look at my anemometer which reported a wind gust of 90-95MPH (not sure how accurate that was though). The next morning, I did a damage survey of my own. The flag that was on our house was ripped off (we had just put it up the day before, and I hung on it to test its strength, and I weigh about 165Lbs). About another 1-mile away, they got hit even harder... Numerous pines were uprooted (large pines), as well as many other trees (if the trees still had their leaves, more damage probably would have occured). A couple mobile homes were also tipped over and a few power poles were even pushed over. The size of the damage area was pretty small, relative to the rest of the squall line - about a 1-2 mile radius. Also, the direction that the winds were coming from varied greately... The anemometer reported rapid changes in wind direction, which probably helped to increase damage (the objects had a better chance of "catching the wind just right").
 
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