Reflectivity at x°C - Warning Decision Training Division (WDTD)

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Reflectivity at x°C

Short Description

The reflectivity on a constant temperature surface.

Subproducts

Reflectivity at 0°C

Reflectivity at -5°C

Reflectivity at -10°C

Reflectivity at -15°C

Reflectivity at -20°C

Primary Users

NWS: WFO, CWSU, AWC

Input Sources

3D Reflectivity Cube

Vertical temperature profile from the current operational NCEP/EMC mesoscale model (i.e., the RAP as of 2015).

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

Isothermal reflectivity products are computed by finding the reflectivity at an altitude corresponding to a certain temperature value (0°C, -5°C, -10°C, -15°C, or -20°C) that was obtained from an analysis of the near-storm environment by a mesoscale model.

At each horizontal 2D grid point, the altitude of the particular 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 isothermal reflectivity at that temperature altitude is then computed by interpolating the reflectivity between the two vertically adjacent grid points.

Technical Details

Latest Update: MRMS Version 10

References

None

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.

The use of mesoscale model analysis data to derive temperature information allows the temperature fields to vary across the domain of interest. This is in stark contrast to applying a single temperature altitude proxy across the entire domain, as is often done for single radar calculations. Thus, MRMS data better captures gradients in the temperature fields over space and time.

Limitations

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).

Applications

Can be used to assess a storm’s severe potential. For example, the presence of reflectivities greater than 50 dBZ near the -20°C isotherm can indicate the potential for hail.

Isothermal reflectivity in the 0°C to -20°C range can be used to infer supercooled large drops (SLD) associated with severe aircraft icing.

Example Images

Fig. 1: Isothermal reflectivity at -20°C, -10°C, and 0°C and Reflectivity At Lowest Altitude (RALA) for
a MCS over North Dakota at 2326Z on 21 July 2014. Several areas within the MCS exhibit reflectivity
values > 50 dBZ in the -20°C to 0°C layer, indicating pockets of stronger updrafts. These localized
regions are ill-defined in the RALA, with reflectivities > 50 dBZ spread over a much broader area.