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MRMS (Multi-Radar/Multi-Sensor System)

What this is

The Multi-Radar/Multi-Sensor System (MRMS) is NOAA's operational system for fusing the US weather-radar network with other sensors into a seamless, quality-controlled gridded mosaic. Fully automated algorithms integrate every NEXRAD/WSR-88D radar (plus Canadian radars near the border) with rain gauges, surface and upper-air observations, lightning detection, satellite, and NWP model fields to produce 100+ decision-support products on a ~1 km grid, updated every 2 minutes over the contiguous US and southern Canada. Products span reflectivity mosaics (including true 3D mosaics), quantitative precipitation estimation, rotation and hail diagnostics, lightning density, and derived hydrologic and severe-weather guidance.

MRMS is an observational/analysis product, not a forecast model — it is a present-state mosaic of what the sensors are seeing, quality-controlled and merged. A small minority of the suite is derived short-range guidance (see Scope note). It became operational at NCEP in 2014 and is the operational successor to the WDSS-II and NMQ research systems. Its output is a foundational input to US operational NWP and hydrology.

Who operates it

  • Operator / coordinating programme: NOAA / National Severe Storms Laboratory (NSSL); operational production at NOAA/NWS/NCEP. Co-developed with the Cooperative Institute for Severe and High-Impact Weather Research and Operations (CIWRO, formerly CIMMS) / University of Oklahoma.
  • Country / region: United States. The primary CONUS domain's composite extends over southern Canada and northern Mexico; separate OCONUS domains cover Alaska, the Caribbean/Puerto Rico, Guam, and Hawaii (served as subtrees under 2D/).
  • Data distributor: NOAA Open Data Dissemination (NODD) via AWS; NCEP real-time HTTP server.

Network composition

Built on the US NEXRAD / WSR-88D network (~160 S-band dual-polarization radars) plus Canadian radars near the border. MRMS is genuinely multi-sensor: beyond radar it ingests rain gauges, surface and upper-air observations, NLDN lightning, satellite, and NWP (RAP) model fields — so the products are a blended analysis rather than raw radar. The grid is a regular latitude/longitude (Plate Carrée) mesh at 0.01° (~1 km); the 3D reflectivity and dual-pol mosaics are provided on 33 CAPPI levels from 500 m to 19,000 m MSL.

Products

Written against the v12.2 product table (151 entries). Most 2D fields update every 2 minutes; accumulations update at their stated windows.

  • Reflectivity mosaics: 2D composite and base reflectivity (optimal-method and max-ref variants), composite-reflectivity height, and Level-III high-resolution echo top (HREET) and VIL. True 3D mosaics — reflectivity (MergedReflectivityQC), RhoHV, and Zdr — each on 33 CAPPIs (500–19,000 m). The 3D gridded mosaics are the key discriminator from a 2D-only radar composite.
  • Precipitation (QPE): surface precipitation type (PrecipFlag), radar precipitation rate, radar-only and multi-sensor (gauge-corrected) QPE, and 1/3/6/12/24/48/72-hour accumulations; plus Radar Quality Index and gauge-influence indices.
  • Rotation / severe: azimuth shear at multiple AGL layers (MergedAzShear0to2kmAGL, 3to6kmAGL) and rotation tracks over multiple time windows; hail (MESH) and related diagnostics.
  • Lightning: NLDN cloud-to-ground density at 1/5/15/30-minute windows (CONUS only) and derived probabilities.
  • Environment / model: surface temperature, wet-bulb temperature, warm-rain probability, and freezing/melting-level heights (from RAP), used in precipitation typing.
  • Hydro (FLASH): flash-flood guidance — streamflow, unit streamflow, soil saturation — derived nowcast/forecast fields (out to ~6 h).
  • Nowcast (ANC): 1-hour reflectivity forecast and next-hour convective likelihood.
  • ProbSevere: object-based severe-storm probabilities, distributed as ASCII/JSON (2 products; not gridded GRIB2).

Data availability

  • Is the data free? Yes — no account, no registration.
  • Is the data downloadable? Yes.
  • Access tier: Open (no account, no registration).
  • Data formats: GRIB2, gzip-compressed (.grib2.gz). ProbSevere as ASCII/JSON (non-gridded).
  • Update cadence: Real-time; 2-minute update cycle for most 2D products.
  • Primary access:
    • NCEP real-time HTTP: https://mrms.ncep.noaa.gov/ — top-level trees 2D/, 3DRefl/, 3DRhoHV/, 3DZdr/, ProbSevere/. The ~150 CONUS products sit directly under 2D/ as per-product subfolders; the OCONUS domains are nested as 2D/ALASKA/, 2D/CARIB/, 2D/GUAM/, 2D/HAWAII/. (RIDGEII/ is rendered imagery — see Notes.)
    • Filename convention: MRMS_<Product>_<level>_<YYYYMMDD>-<HHMMSS>.grib2.gz, timestamped in UTC at the 2-minute cycle. <level> is 00.00 for 2D surface fields; the 3D*/ trees carry per-CAPPI-level files. A rolling MRMS_<Product>.latest.grib2.gz in each folder always points to the most recent file.
      • Example (timestamped): https://mrms.ncep.noaa.gov/2D/PrecipRate/MRMS_PrecipRate_00.00_20260706-020000.grib2.gz (~627 KB)
      • Example (rolling latest): https://mrms.ncep.noaa.gov/2D/PrecipRate/MRMS_PrecipRate.latest.grib2.gz
    • AWS Open Data: s3://noaa-mrms-pds (region us-east-1, no account: aws s3 ls --no-sign-request s3://noaa-mrms-pds/); browse at https://noaa-mrms-pds.s3.amazonaws.com/index.html. Mirrors the same product/domain layout and filename convention.
  • New-data notifications: SNS arn:aws:sns:us-east-1:123901341784:NewMRMSObject (Lambda and SQS protocols only).
  • Archive depth: The NCEP HTTP server is a short rolling real-time window; the AWS bucket holds the operational archive. Note the v11→v12 break on 14 October 2020 (below) — treat pre-2020 v11 holdings with caution.
  • Licence: NOAA Open Data Dissemination (NODD) — open to the public and usable as desired; as a U.S. Government work, effectively public domain (CC0-equivalent). Attribution requested; no stating or implying NOAA endorsement; modified data must not be presented as original, unaltered NOAA data.

Scope note

  • Observation vs forecast. MRMS is predominantly an observational/analysis mosaic (reflectivity, QPE, rotation, lightning) and belongs in the observations section on that basis. The suite bundles a small set of derived short-range guidance — FLASH flash-flood forecasts (to ~6 h) and the ANC 1-hour reflectivity nowcast. These are noted rather than excluded; the core product identity is observational.
  • Legacy NMQ sharing policy is superseded. An older "MRMS/NMQ Dataset Sharing Policy" (Gourley & Howard, NSSL) carries restrictive language — requests not to redistribute without NSSL permission and not to duplicate methods to mimic the dataset. That document governs the experimental NMQ research data streams and does not apply to the operational product, which is distributed under NODD's open terms. The License field above reflects the operational feed; the NMQ policy is legacy and non-applicable here.
  • Software vs data. The University of Oklahoma retains commercial-licensing rights to the MRMS software. This concerns the processing code, not the output data — the operational data itself carries no such restriction.

Notes

  • Multi-sensor, not raw radar. MRMS blends radar with gauges, lightning, satellite, and RAP model fields — it is a merged analysis, and QPE in particular is a multi-sensor product.
  • Relationship to NWP and hydrology. MRMS reflectivity and QPE feed operational US systems — radar reflectivity assimilation in HRRR/RAP, and rainfall input to hydrologic and flash-flood modeling — closing the loop with those model entries.
  • Data feed vs viewer. RIDGEII/ on the NCEP server is the RIDGE II imagery/tile service (rendered raster), not gridded data — viewer-only and out of scope. The gridded feed is 2D/ and the 3D*/ trees.
  • Version caution. The v11→v12 upgrade (14 Oct 2020) added and discontinued products and changed the underlying science; this entry is written against the v12.2 table. Cross-version time series should account for the break.
  • Two non-GRIB2 products. The ProbSevere ASCII/JSON products are object-based, not gridded — flag if the catalog prefers to scope the entry to the GRIB2 gridded suite only.

Recent version history

  • 14 October 2020 — v11 → v12: new products introduced, others discontinued, science and QC upgraded across the suite. Subsequent v12.x minor updates followed (current product table: v12.2).
  • 2014: MRMS became operational at NCEP, superseding the WDSS-II / NMQ research systems.

Official documentation