MRMS Rotation Tracks Explained — Azimuthal Shear, Cyclic Supercells, Damage Surveys

MRMS Rotation Tracks Explained — Azimuthal Shear, Cyclic Supercells, Damage SurveysHow to read NSSL's MRMS Rotation product — rolling 30-min, 1-hour, and 24-hour max azimuthal shear maps that show where rotation has been. Used for post-event surveys, cyclic supercell tracking, and QLCS spin-up identification.MRMS — Multi-Radar Multi-Sensor — is the NSSL system that merges every NEXRAD site's data into one seamless mosaic. The Rotation product takes this a step further: it computes azimuthal shear at every grid point and tracks the maximum value over rolling time windows. That gives you a post-event "where was the rotation?" map, not just a now-cast.The time windowsFrom the Product Type list, pick "Rotation," then choose a rolling window from the right-side menu:

Instantaneous (ROT): Right-now azimuthal shear. Useful in real time, but flickers as scans cycle.

30-min max: Smoothed track of rotation in the last half hour. The most useful operational view.

1-hour max (ROT_60M): BloomWX's deep-link default. Captures most cyclic supercells' track within a typical chase.

2-hour max: Wider window — useful for storms that have just exited a county, where you want to see what passed through.

24-hour max: Post-event survey view. Did the warned rotation actually track where the warning polygon was?

7-day max: Climatological / event-period summary. Rare but useful for outbreak retrospectives.

The color scale

Green: Weak shear (~0.005 / s). Often non-meteorological or marginal supercell rotation.

Yellow: Moderate shear. Mid-level meso, low-end significant.

Orange: Strong shear. Significant rotation; possible / likely tornado warning territory.

Red: Very strong shear. Tornadic supercell range.

Purple / pink: Exceptional shear. Strong-tornado producers.

What it's NOT

Not a tornado track. Rotation aloft doesn't guarantee a tornado at the surface. The track shows where the radar saw rotation; whether that rotation reached the ground is determined by storm survey + LSRs.

Not a real-time warning tool. The product has a small latency. Use NWS warnings for life-safety decisions.

Not great close to the radar. Within ~10 km of a NEXRAD site, cone-of-silence + range-folding artifacts can produce false rotation signals.

Not perfect at long range. Beyond ~150 km from a radar, beam height grows and weak rotation gets lost above the surface circulation.

How spotters / EMA actually use it

Post-event verification: "Did the warned rotation track over the area where damage was reported?" Pair with LSRs.

Cyclic supercell tracking: A storm that produces multiple tornadoes typically shows multiple discrete rotation tracks separated by gaps where the meso was occluding and re-organizing. The 1-hour view makes those cycles obvious.

QLCS spin-up identification: Brief tornadoes embedded in a squall line show as small, fast-moving rotation maxima. Easy to miss in real time; obvious in the 1-hour track.

Damage survey planning: Before driving out for an NWS damage survey, the 24-hour rotation track tells you where to focus.

Source: mrms.nssl.noaa.gov/qvs/product_viewer/. BloomWX deep-links to the 1-hour rotation max. The viewer is interactive.Part of the BloomWX learn library — beginner-friendly explainers covering every surface of the BloomWX weather dashboard. Open BloomWX to see live data for any U.S. county.