NOAA MRMS 0-2 km Azimuthal Shear Analysis

GribStream Code: mrmsazshear

Official source: NOAA NSSL publishes MergedAzShear0to2kmAGL as an operational MRMS severe-weather product. GribStream reads the public NOAA Open Data Dissemination bucket without mirroring or resampling the field.

Current GribStream scope: mrmsazshear provides the CONUS 0-2 km azimuthal-shear analysis on its native 14,000 by 7,000 grid. Historical coverage begins October 14, 2020 and grows forward, with a nominal two-minute source frequency.

Interpretation: Azimuthal shear is a radar-derived rotation diagnostic. It can highlight organized rotation, but it is not a tornado observation, tornado probability, warning, or standalone decision rule.

Description

MRMS 0-2 km azimuthal shear summarizes radar-derived rotational shear in the lowest two kilometers above ground level across a seamless CONUS mosaic. It is one of the system's severe-weather diagnostics and updates quickly enough to support monitoring of evolving convective storms.

The field is most useful as context. Rotation embedded in a persistent storm, collocated with strong reflectivity, hail signatures, lightning trends, environmental support, and official warnings has a different meaning from an isolated pixel. Products should preserve that distinction instead of presenting azimuthal shear as a direct tornado detector.

NOAA distributes this field at twice the linear grid density of the five products in mrms. A 14,000 by 7,000 field contains 98 million cells, so GribStream exposes it as mrmsazshear with its own coordinate index rather than mixing incompatible grids.

The source uses 0 for missing, range-folded, and no-coverage cells in this product. That convention is specific to MRMS azimuthal shear; GribStream maps those cells to null without treating zero as missing in unrelated datasets.

Use /api/v2/mrmsazshear/timeseries for coordinate histories and /api/v2/mrmsazshear/runs for exact-time or gridded extraction. Source timestamps include seconds and appear unchanged in the API.

Detail

• Archive begins: 2020-10-14
• Official MRMS GRIB2 table: https://www.nssl.noaa.gov/projects/mrms/operational/tables.php
• Key features:
  • Native MergedAzShear0to2kmAGL values in 0.001/s, preserving NOAA's operational parameter name and source unit.
  • Regular 0.005 degree latitude-longitude spacing, approximately 500 m north-south, with 98 million cells per field.
  • Nominal two-minute updates with exact source timestamps retained to the second in both forecasted_at and forecasted_time; horizon remains 0.
  • NOAA defines zero as missing, range-folded, and no-coverage for this product. GribStream returns those source-convention cells as null.
  • The separate dataset code prevents 0.005 degree coordinates from being indexed against the 0.01 degree MRMS radar and precipitation grid.
• Resolution: Regular 0.005 degree CONUS latitude-longitude grid with 14,000 columns by 7,000 rows, covering 20.0025N to 54.9975N and 129.9975W to 60.0025W. The north-south spacing is approximately 0.56 km; east-west ground spacing varies with latitude.
• Temporal coverage: Nominal two-minute source frequency. GribStream preserves each observation timestamp to the second; historical coverage begins October 14, 2020 and grows forward.
• Primary uses: Rapidly updating storm-rotation displays, mesocyclone screening, severe-weather alert enrichment, storm tracking and verification, aviation and event operations, research, and combining rotation diagnostics with reflectivity, MESH, lightning, warning polygons, or convection-resolving forecasts.

Related datasets

• MRMS composite reflectivity, MESH, precipitation, QPE, and RQI
• HRRR for convection-resolving short-range forecasts
• RAP for frequently updated North American forecast context
• SPC tornado guidance for calibrated forecast probabilities

Parameters