SPC Beta Analysis

Data Courtesy Storm Prediction Center

SHERBE

The SHERBE is a normalized composite parameter intended to identify the potential for significant damaging winds and tornadoes in low CAPE, high shear environments typical of the southeast U.S. cool season.

This formulation of SHERBE inherently accounts for at least weak buoyancy by utilizing the EBWD (which requires an effective inflow layer), which tends to reduce false alarms compared to the original version of SHERB using the fixed-layer 0-3 km shear. Still, the parameter can suggest an over-estimate of the severe weather threat in areas of relatively steep 0-3 km lapse rates which overlap with the 700-500 mb layer in the vertical.

Modified SHERBE

The Modified SHERBE is a composite parameter designed to highlight "low CAPE/high shear" environments capable of producing significant severe storms.

This composite parameter indirectly includes some influence of buoyancy through the effective bulk shear term, which requires at least 100 J kg-1 of CAPE and no more than 250 J kg-1 of CIN. Overall, MOSHE represents and improvement to the original SHERB parameters developed by Sherburn et al. (2014), primarily through reduction in false alarm area. Please note that this parameter formulation is very sensitive to the magnitude of vertical velocity, and may not translate well between differing modeling systems (e.g., the RAP model versus a convection-allowing model).

Craven-Wiedenfeld Aggregate Severe Parameter

This aggregate parameter is the sum of 33 individual weighted parameters, ranging from mandatory pressure level winds, temperature and moisture, to CAPE and vertical shear. Typical ranges of values were established for each parameter in association with significant tornado (EF2+) events, and a numerical weight of 0-3 was assigned to each parameter. If all parameters are consistent with historical EF2+ tornado events, the CWASP total will reach a maximum value of 99. The majority of EF2+ tornadoes have occurred with CWASP values above about 70.

Tornadic 0-1 km EHI

This updated version of the 0-1 km EHI adds 0-3 km mlCAPE and 0-6 km bulk wind difference as enhancing factors, and LCL/CIN as limiting factors. Because EHI values are often deceptively large over wide areas when other factors suggest reduced potential for tornadic supercells (such as weak 0-6 km bulk wind difference, high LCL heights, or large nighttime CIN), this modified version of EHI should consolidate areas supporting tornadic supercells (values of 1-2 or greater). The inclusion of 0-3 km mlCAPE also helps identify areas with greater potential for low-level stretching, even if total mlCAPE is relatively small.

Tornadic Tilting and Stretching parameter (TTS)

TTS is a parameter developed by Jon Davies that focuses on storm-relative helicity in the lowest 1 km (SRH1) and 100 mb mixed-layer CAPE in the lowest 3 km above ground level (mlCAPE3). The presence of both ingredients suggests potential for increased low-level tilting and stretching of horizontal, streamwise vorticity within updrafts, which may increase the potential for tornadic supercells. Enhancements are added based on total CAPE and deep-layer shear that strengthen updrafts; LCL height and CIN are used as limiting factors when they are too high or large, respectively. In preliminary testing, values approaching 2 and greater suggest potential for tornadic supercells. This experimental parameter is intended to help diagnose environments supporting tornadoes where total CAPE is relatively small, such as during the cool season.

Dendritic Layer (Omega * PW * RH)

The product of vertical motion, precipitable water, and relative humidity in the dendritic growth layer. Values will be most negative (favorable for snow growth) where strong ascent coincides with saturation in the dendritic growth layer.

Conditional Probability of EF0+ Tornadoes

The conditional probability of EF0+ tornadoes given a right-moving supercell, based on the grid-point value of effective-layer STP. The probabilities are derived from a mutually exclusive 2014-2015 sample of right-moving supercells that produced tornadoes, large hail, and damaging winds. The probabilities are plotted as grid point values (rounded integer %), with color coding related to the climatology of the sample. For example, brown denotes values lower than the sample climatology, and yellow is near climatological EF0+ frequency. Red, magenta, and dark purple values are all increasingly larger than the climatological EF0+ frequency.

Conditional Probability of EF2+ Tornadoes

The conditional probability of EF2+ tornadoes given a right-moving supercell, based on the grid-point value of effective-layer STP. The probabilities are derived from a mutually exclusive 2014-2015 sample of right-moving supercells that produced tornadoes, large hail, and damaging winds. The probabilities are plotted as grid point values (rounded integer %), with color coding related to the climatology of the sample. For example, brown denotes values lower than the sample climatology, and yellow is near climatological EF2+ frequency. Red, magenta, and dark purple values are all increasingly larger than the climatological EF2+ frequency.

Conditional Probability of EF4+ Tornadoes

The conditional probability of EF4+ tornadoes given a right-moving supercell, based on the grid-point value of effective-layer STP. The probabilities are derived from a mutually exclusive 2014-2015 sample of right-moving supercells that produced tornadoes, large hail, and damaging winds. The probabilities are plotted as grid point values (rounded integer %), with color coding related to the climatology of the sample. For example, brown denotes values lower than the sample climatology, and yellow is near climatological EF4+ frequency. Red, magenta, and dark purple values are all increasingly larger than the climatological EF4+ frequency.