This is the second time in the past 9 days that the midwest, especially Oklahoma, has seen a major tornado outbreak. Both times the Storm Prediction Center has put the area in a High Risk, and issued a tornado watch box that was classified as a “Particularly Dangerous Situation.”
After a few days of traveling and getting things settled, I have finally found myself down in Cape Canaveral just a few miles south of the Kennedy Space Center. I’ll be spending the next 10 weeks doing research for the Convective Wind project. I just hope the sun won’t kill me down here. For pics of the place, go here.
Onto some weather related news. A gentelman over at Weather Graphics has provided a very extensive report of the weather conditions prior to and during the onset of crash. Thanks to my Florida roomate Mitch for showing me this.
You can view the report here
10 years ago today one of the worst tornado outbreaks in the United States occured. On the evening of May 3rd, 1999, 66 tornadoes were reported in Oklahoma and Kansas, killing nearly 50 people.
The biggest tornado to touch down was evaluated as an F5 tornado, and blasted through Moore, Oklahoma…just 10 miles north of the OU campus. Here is what the supercell looked on radar imagery. If you wanted to know what a supercell looks likes…this is probably the best example out there (SOURCE: Wikipedia):
The sounding that morning (approximately 12 hours before the tornado outbreak) indicated favorable conditions for tornadic supercells (SOURCE: Plymouth State):
This sounding is a perfect example of a loaded gun sounding. What do I mean? Well the red line is the environmental temperature, in other words, what the temperature is as the weather balloon goes up. Notice near the bottom the red line shifts sharply to the right. This indicates a strong temperature inversion, or a “cap”. Now this sounding was taken at 12 Z which is approximately 7am in Oklahoma. If you can get daytime heating of the surface during the day, then you might be able to “break the cap” and create an extremely unstable atmosphere, which is conducive for severe weather.
Also note the thermodynamic values at 7am local time:
When daytime heating occurs, those values are likely to get higher (or lower in the case of LI), which can help create an unstable atmosphere.
Also notice how winds are turing clockwise with height. This is an indication of strong verring wind shear, which can help structure a cell to become a supercell, and in this case, a tornadic cell
So we have an unstable atmosphere, now we need two other ingredients: moisture and a lifting mechnasim. We can get those two by looking at the 850mb map (SOURCE: Storm Prediction Center)
The brown lines are isoheights. Notice the sharp cyclonic “u-shape” area just west of Oklahoma. This is an upper level trough, which can act as a lifting mechanism. Also notice the green lines. These are areas of high Dewpoint. The blue wind barbs indicate that the southerly flow is bringing a moist airmass into the area. This is what we like to call a “low-level jet”. This day is a classic example of “how to create tornadic supercells”
While May 3rd is considered a holiday for some meteorologists, we must remember that people’s lives changed that day. Over the past 10 years, improvements on weather detection, such as high res models (RUC, WRF), and advances in radar (MPAR, CASA, Dual Pol) have been created to warn the public of these kinds of events. While we have gotten better, more work needs to be done, and I hope to be a part of that somehow.
For my Transportation Project: Aviation Sector, I did a case study about the plane crash on the evening of February 12th, 2009. Before I go on, I would like to say that this is not published work, and the investigation by the NTSB is not finished.
Here are some of the weather conditions that evening that may have contributed to the crash:
These are all good conditions that clear ice, the most dangerous form of ice for an aircraft, will form. While an NTSB’s report on March 25th 2009 (source) said that icing was occurring that evening, it was not the main factor.
Nonetheless this is a tragic story and weather can be very nasty at some times.
OK so I have not done one of these in a long time, but we had an interesting weather event over the past few days. This system that passed through the US not only caused the tornado outbreak Tuesday, but also gave New England abnormally high temperatures.
When doing a case study, it’s good to start large scale, then move down. So let’s start at the upper levels
The above is the 850mb map from Tuesday night (SOURCE: Storm Prediction Center). We can see a very narrow trough over the center US. This trough is generating strong southerly flow downstream of the trough. This flow is bringing warm moist air over the Oklahoma area, indicating areas of strong WAA, which induces rising motion, which helps generate precipitation. Now look at this trough 24 hours later:
It has moved towards the northeast, but it is still bringing warm air towards the New England area, which helps explain why we had temps in the 50′s and even 60′s for areas of southern New England.
Now let’s move on to the tornadic situation. The SPC has gotten 6 tornado reports on Tuesday night (including one near Pawnee Oklahoma….sound familiar?) . Let’s take a look at a sounding launched that evening in Norman, Oklahoma:
The red line is the actual temperature recorded by the weather balloon, and the yellow line is the parcel temperature (the temperature if a air parcel rose from the surface to the top of the atmosphere). The general rule of thumb is if the parcel temperature is GREATER than the environmental temperature (yellow line to the right of the red line), the parcel will continue to rise on its own. So if we have some sort of lifting mechanism (like a strong cold front or WAA at low levels…which in this case, we do), then we can get strong vertical motion which can induce severe weather.
Also note some of the severe weather indices on the right hand side of the chart:
Needless to say this storm brought some devasting damage for the eastern parts of Oklahoma, and also caused the ice on the roof of my house to fall overnight last night!
