Sunday, July 17, 2011
StormTrack: July 17: Iowa Single-Cell Storms (Morning)
TERMS TO KNOW
CAPE: A measure of instability. 2000+ values considered unstable.
LI: Lifted Index- another measure of instability. Negative values considered unstable.
EHI: Energy Helicity Index. A measure of tornado potential.
VGP: Vorticity Generation Potential
SRH: Storm Relative Helicity. Detects cyclonic motion in thunderstorm updrafts. Considered dangerous at levels above 200.
Looking at current observations, I am seeing the atmosphere as dangerous. It looks like the Lifted Index (A measure of instability) is down into -10, which is very unstable. That coupled with CAPE values of over 5000, makes the atmosphere very rambunctious. One more concerning thing is something called an EHI. Thunderstorms form when warm air rises vertically. Energy. That's the E in EHI. Helicity is the spinning motion that could occur as this warm air rises, priming the environment for potential tornadoes. That's the H. Put them together and we have the Energy Helicity Index. EHI combines both CAPE and Helicity. SRH values are currently at 250 in North Iowa.
All this information put together indicates a tornado potential. However, there are several roadblocks. Shearing is nonexistent in some parts of North Iowa. That kills tornado potential and basically ends hope for tornadoes. But then again, you never know if these parameters do indicate a tornado could occur.