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http://www.spc.noaa.gov/products/outlook/archive/2017/day1otlk_20170504_1300.html

http://www.spc.noaa.gov/products/outlook/archive/2017/day1otlk_20170504_2000.html

A quick look at the MLCAPE plots with locations the tornadoes in regions of MLCAPE of 250 J/kg or less (https://cimmse.files.wordpress.com/2017/09/fig16.png and https://cimmse.files.wordpress.com/2017/09/fig8.png) demonstrates the limitations with traditional analysis. The SHERBE and MOSHE appear to provide a better context and additional information (https://cimmse.files.wordpress.com/2017/09/fig13.png and https://cimmse.files.wordpress.com/2017/09/fig20b.png).

]]>Thanks for the comment. I appreciate you bringing this to my attention, as I hadn’t read the “fine print” description of the parameter on the SPC Mesoanalysis page yet.

The intent of the MAXTEVV term is to combine the potential instability in a layer with the vertical velocity at the top of that layer in order to approximate the release of potential instability. We calculated this over layers from 0-2 km to 0-6 km at a 0.5-km interval. In other words, the MAXTEVV is the maximum product of the vertical theta-e difference over 0-2 km, 0-2.5 km, 0-3 km, 0-3.5 km, …, 0-6 km layers multiplied by the omega at 2 km, 2.5 km, 3 km, 3.5 km, …, 6 km, respectively.

The caption on the Mesoanalysis page implies that the MAXTEVV term may be calculated in a different way in the MOSHE there. As you noted, their formulation, as described, would allow for a vertical offset of potential instability and omega, which is not what we intended. I’ve contacted the SPC folks and will relay what I hear from them.

Thanks again!

-Keith

MOSHE = ((0-3 km lapse rate – 4 K km-1)2 / 4 K2 km-2) * ((0-1.5 km bulk shear – 8.0 m s-1) / 10 m s-1) * ((effective bulk shear – 8 m s-1) / 10 m s-1) * (MAXTEVV + 10 K Pa km -1 s-1) / 9 K Pa km-1 s-1)

where MAXTEVV is the maximum product of theta-e decrease with height and upward motion over a 2 km deep layer from the surface to 6 km AGL .

1) So I’m thinking about this correctly… MAXTEW is the maximum value one would obtain by finding the greatest -d(Theta-E)/d(Z) over a 2km layer between 0-6 km multiplied by the greatest upward motion (presumably omega?) over a 2km layer between 0-6 km. Is this correct?

2) Is the max 2km upward motion confined to the 2km layer of maximum -d(ThetaE)/d(Z), or is the max 2km upward motion unbounded by the max -d(ThetaE)/d(Z) layer? In other words, can the max 2km upward motion come from, say, the 4-6 km layer, while the greatest -d(ThetaE)/d(Z) comes from, say, the 1-3 km layer.

IF this is the case, e.g. the max 2km layer of forcing is displaced from the max 2km layer of potential instability, (all else being equal) would the release of potential instability be reduced in magnitude? Would it be released at all? Is there a certain degree of “overlap” that must be present between the max 2km layer of omega and max 2km -d(ThetaE)/d(Z) layer for potential instability contained therein to be released?

Brandon Vincent

Meteorologist

NWS Raleigh, NC