Posted May 27, 2008
A massive tornado plowed through northern Colorado on May 22. It did lots of destruction in the town of Windsor which is about 60 miles north of Denver. I just can't believe a tornado that powerful would dare hit this beautiful area of Colorado. What I want to do is show the model images from the time closest to when the tornado hit and go over the synoptic causes of this massive tornado.
The image below is 300 mb. Notice there is a sort of Omega block over the U.S. The ridge in the central U.S. is blocking the trough in the western U.S. from making much progress toward the east. This results in a slow moving weather pattern. Since the upper low is blocked over the mountains, this allowed moisture and warmth to advect right up to the mountains. Thus, eastern Colorado stayed in the warm sector.
The image below is 500 mb. It is showing a region of PVA over central and northern Colorado. This is important in that it promotes rising air. This only helps storms. The winds aloft are also strong enough to help exhaust the updraft. This helps storms last longer and allows them to become more intense.
This next image is of great significance. So much can be said about it. Severe storms often form on boundaries. Notice in northern Colorado the winds are from the east and in central Colorado the wind is from the southeast. There is a clear convergence boundary where the air streams are converging into each other. This helps focus storms. This is right where the tornadic storm formed. This area is where a warm front would be found in association with a low pressure system. You can see this by the warm temperatures south of the boundary and cooler temperatures north of the boundary. The boundary acts as a shear axis. A tornadic environment will have low level shear. You can also see as mentioned earlier the warm sector moving right up to the mountains due to the low being blocked over the mountains.
The next image shows that the air over Colorado was unstable. This allows storm updrafts to occur when air rises. The warm air moving in at the surface with the cool air aloft will cause instability.
Some additional images I saved are below: 700 mb, surface pressure, and Denver morning sounding