Charlotte, NC tornadoes and a look ahead
Well, it's nearing the end of the rainy season for northern California, and we experiencing yet another Pacific storm in San Francisco. Of course, these storms don't dissappear once they move past the Sierras, they keep moving east, and this one has the possibility of bringing severe weather to the southern Plains. Meteorologists at the Storm Prediction Center believe that conditions at the surface will be favorable for severe wx in a region reaching from the Texas Panhandle northeastwards towards Iowa on Thursday. However, a warm layer aloft known as the cap may be strong enough to prevent storm formation. Conditions look slightly more favorable for Friday in a region extending south from north Texas along the Edwards plateau. The forecast wind profiles suggest that squall lines are more likely near Dallas/Fort Worth with supercells possible towards the south.
The severe weather season hasn't been completely quiet so far this year. Two tornadoes occured near Charlotte, NC on March 28, 2010. The first tornado touched down at 544 EDT near Belmont, NC. It was rated an EF-1 (description of the Enhanced Fujita scale)tornado with estimated wind speeds of 90 mph. The TDWR at Charlotte had an excellent view of the storm (a classic supercell, to be precise)
Fig. 1 Reflectivity data from TCLT on March 28.
Figure 1 is a high-resolution view of the hook echo associated with the tornado. This is one of the more impressive hook echoes I've seen on radar (comparable to results obtained using the Doppler on Wheels). Hook echoes are produced when the rotating winds of a mesocyclone wrap precipitation away from the storm's main body. These rotating winds can be detected using Doppler data.
Fig. 2 Radial velocity from TCLT on March 28
Figure 2 shows the Doppler radial velocities (towards/away from the radar site) for the same area as Figure 1, and a shear couplet is in the same area of the hook echo. This means that in a short area of space, the winds shift from going towards the radar to going away in a pattern that indicates rotation.
This particular case is also useful in demonstrating the value of having a dense radar network. The nearest NEXRAD radar is located at Greenvile, SC and it did not have such a good view of the storm.
Fig. 3 Reflectivity data from KGSP on March 28
The most striking thing in this image is that the hook echo is not visible in this image. This isn't too surprising since at this distance, the radar beam is 6,000 feet above the ground, and hook echoes are low-level features.
Fig. 4 Radial velocity from KGSP on March 28
However, the radial velocity data show the presence of a mesocyclone at the mid-level of the storm, which is useful for warning purposes. For Charlotte's TDWR, the beam height at the hook echo is only 230 feet, so it has the superior view of what going on near the surface. It's interesting to note that Charlotte's TDWR was among the first TDWRs to send data to the NWS for the improved low-level coverage near Charlotte.
The next two images show animations of the data, and it is striking to watch the hook echo coil up and collide with it's parent storm.
Fig. 5 Animation of reflectivity data from TCLT on March 28
Fig. 6 Animation of Doppler velocity data from TCLT on March 28
The second tornado touched down at 645 PM EDT near Spencer, NC. The NWS rated it an EF-1 tornado, and it had a maximum width of 0.5 miles and a path length of 3.3 miles. The TDWR in Charlotte had a less favorable view of the storm that produced this tornado.
Fig. 7Reflectivity data of the Spencer tornado at 644 PM EDT
A hook echo is apparent in the reflectivity data. While this storm has the form of a classic supercell, it's rather small.
The mesocyclone that produced the tornado is also apparent in the Doppler radial velocity data. All of the radar visualizations in this entry were produced using the Weather and Climate Toolkit from the National Climatic Data Center.