Height of xx dBZ Echo Above x°C - Warning Decision Training Division (WDTD)

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Height of xx dBZ Echo Above x°C

Short Description

The altitude difference (thickness) between a specified echo top (ET) and a specified temperature.

Subproducts

Height of 50 dBZ Echo Above -20°C

Height of 60 dBZ Echo Above -20°C

Height of 50 dBZ Echo Above 0°C

Height of 60 dBZ Echo Above 0°C

Primary Users

NWS WFO

Input Sources

3D Reflectivity Cube

Vertical temperature profile from the current operational NCEP/EMC mesoscale model (i.e., the RAP as of 2014).

Resolution

Spatial Resolution: 0.01^o Latitude (~1.11 km) x 0.01^o Longitude (~1.01 km at 25^oN and 0.73 km at 49^oN)

Temporal Resolution: 2 minutes

Product Creation

At each horizontal 2D grid point, the altitude of the specified temperature value (e.g., 0°C) is checked from the top-down. Once the temperature value becomes greater than the temperature being searched for, the altitude is computed by interpolating between the current level and the previous higher level. This calculation method accounts for low-level inversions in the temperature profile by specifically targeting altitudes that are associated with deep convection (e.g., elevated convection over shallow cold layers).

The reflectivity thickness is computed by subtracting the temperature level altitude from the xx dBZ Echo Top altitude.

Technical Details

Latest Update: MRMS Version 11.5

References

Cavanaugh, D. E., and J. A. Schultz, 2012: WSR-88D signatures associated with one inch hail in the Southern Plains. Electronic J. Operational Meteor, 13 (1), 1-14.

Donavon, R. A., and K. A. Jungbluth, 2007: Evaluation of a technique for radar identification of large hail across the Upper Midwest and Central Plains of the United States. Wea. Forecasting, 22, 244-254.

Strengths

Like all MRMS products, the use of multiple radars is more robust than single-site radar alone. It provides faster updates and helps the forecaster integrate data from multiple radars. It also compensates for cone-of-silence, beam broadening at far ranges, and terrain blockage.

Limitations

The AWIPS “Height of the 0°C Isotherm” is referenced to mean sea level (MSL) making it cumbersome to use the Cavanaugh and Schultz (2012) table (Fig. 1) or graph (Fig. 2), which uses AGL. Maximum Estimated Size of Hail (MESH; particularly the MESH “Meteor Trails” visualization technique) is much better and easier to use in an operational warning environment.

Subject to the biases and deficiencies of the mesoscale model used to derive the vertical temperature profile.

Quality Control

This product is derived from the 3D Reflectivity Cube, which means non-hydrometeorological data has been removed including: Ground clutter, anomalous propagation (AP), chaff, interference spikes, and bioscatterers (e.g., angels and ghosts). However, bright band contamination remains.

Applications

Positive values imply strong updrafts are present with large reflectivity values at high altitudes.

Negative values imply the storms are shallow, but could be growing.

Building on previous research by Donavon and Jungbluth (2007), a study by Cavanaugh and Schultz (2012) indicated the altitude of the 50-dBZ reflectivity echo relative to the melting level was the most effective 1-in (severe) hail detection method (Figs. 1 and 2) of the four they tested. The 25th percentile threshold was found to score the best.

Fig. 1: Severe hail warning criterion from Cavanaugh and Schultz (2012) using the
50 dBZ Echo Top (ft; AGL) and the height of the melting level (ft; AGL).

Fig. 2: Graphical representation of hail warning criteria from Cavanaugh and Schultz
(2012) using the 25th percentile threshold of the Reflectivity Thickness and the
height of the melting level AGL. Yellow (blue) shaded region indicates storm is above
(below) warning criterion.

Example Images

Fig. 3: Height of xx dBZ Echo Above x^oC for a short-lived severe thunderstorm over North Dakota at
2110Z 21 Jul 2014. See panel legends for details. SPC storm reports indicate 1.75-in hail was reported
from this storm at approximately this time.