Interesting Weather Information

Monday, July 24, 2017

Tornado Warning 2017.07.07 by @NWSILN - No Tornado but a Good Warning Part III

PART III - 3D Views

3d view of the supercell from the southeast at 21:17:26z. All reflectivity values >+ 52.5 dBz in solid red represent the core of the storm and the heavy rain. Lower reflectivity values are translucent to show general storm structure and higher values are not visible. KILN Radar using GR2Analyst.

 The Bounded Weak Echo Region (BWER) is clearly visible. This is where there is little or no rain due to the warm, moist inflow and the intense, rapid updraft. The rain drops cannot fall through the updraft because it exceeds their terminal velocity. The BWER was formerly called the vault or echo free vault.

The inflow and updraft. The inflow not only transports warm, humid air into the storm but it imports rotation gained from the environment caused by wind shear. The mechanism is partly explained in Part II and more fully explained here:

I have now added NROT (normalized rotation we call it N-ROT) to the image. Normalized Rotation was originally developed at SPC and operationalized by Gibson Ridge Software in GR2Analyst. I have found it a remarkably accurate and useful tool in pinpointing tornadoes, even small leading edge spin-ups. This confirms the updraft is rotating.

The final overlay is Spectrum Width which can be roughly understood by calling it turbulence. Imagine a wind blowing in a constant direction and at a constant velocity - that is no gustiness - that ideal wind has a spectrum width value of ZERO. In other words it is not gusty. Now imagine a turbulent tornado or severe thunderstorm updraft environment. Winds are changing direction and gusting violently. In other words the environment is turbulent and the spectrum width is high.  Spectrum Width measures the spread or variation of wind speeds and directions. Above, red is very turbulent and notice how it is in the same location as the updraft and rotation.  Spectrum width is a useful tool when trying to locate tornadoes and severe thunderstorm winds and identifying strong updrafts.

The 3D volumetric time lapse shows the evolution of the supercell and how spectrum width and NROT coincide with the rotating updraft.

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