Nexrad Radar Visualization

NEXRAD Radar Visualization

Overview

Create scientifically legible plots from verified NEXRAD single-site products and decoded radar mosaics. Preserve site or domain, product, observation or valid time, units, geometry, quality masking, and color meaning so a visually compelling image cannot hide a wrong quantity or misleading spatial interpretation.

Use this skill after nexrad-product-access or another trusted source has provided a decoded site product. Use nexrad-mosaic-access to retrieve an official MRMS composite before plotting it. This skill does not discover or download radar files.

When to Use This Skill

• Plot base reflectivity, radial velocity, spectrum width, or another decoded Level II moment for one NEXRAD site.
• Plot a Level III product selected by product code and scan time.
• Plot a decoded NOAA/NCEP MRMS or other documented NEXRAD-derived gridded composite while preserving its grid, coverage, and product semantics.
• Create a lowest-elevation PPI, a specified-elevation PPI, or a sweep chosen for a target height.
• Plot dual-polarization moments with appropriate units and masks.
• Create RHI, cross-section, tilt, storm-relative, or multi-sweep views.
• Build a time sequence or animation from a verified scan series.
• Export the plot with a stable color scale, map context, metadata, and provenance.

Do not use a plot to hide a missing sweep, unverified product, invalid gate mask, geolocation error, or unsupported extrapolation.

Define the Visualization Contract

Record:

• radar site and site coordinates;
• data level and exact product or moment;
• observation, volume, or product time in UTC;
• source identity and local content hash when required;
• intended view: PPI, RHI, cross-section, tilt, comparison, or animation;
• sweep or angle policy;
• map projection, bounds, range rings, and landmark context;
• physical units, color scale, display range, and normalization policy;
• invalid, missing, folded, clutter, or otherwise masked gates;
• for gridded mosaics, the provider, product/domain, grid projection and orientation, valid-time semantics, and source/coverage or quality fields;
• output format, dimensions, background, and whether figures are for analysis or publication.

If the user asks only for “a radar image,” produce a useful default: a single-site PPI with site marker, UTC time, product, units, color bar, range rings, and missing-data treatment visible. For a decoded mosaic, use a map view with the product, domain, valid time, units, legend, and missing-data treatment visible. Ask only when product, site/domain, or time would materially change the result and cannot be inferred safely.

Validate Before Plotting

1. Confirm the decoded site, product or moment, time, units, dimensions, and projection.
2. Apply scale, offset, calibration, fill values, and quality flags before interpolation, contouring, or thresholding.
3. Confirm that the requested sweep exists. For a target-height sweep, compute or obtain beam height as a function of range and show which elevation is nearest.
4. Preserve no-data and invalid-data cells as masked values. Do not replace them with zero, minimum reflectivity, or an opaque background that resembles weak echo.
5. Confirm that map coordinates and radar polar coordinates share the correct projection and origin.
6. Record whether velocity is dealiased and whether dual-polarization fields have their documented quality masks.

Plot a PPI

For a plan-position indicator:

1. Select the requested sweep or the lowest usable sweep under a stated policy.
2. Convert range and azimuth to the selected map projection.
3. Mask invalid, below-threshold display, folded, clutter-contaminated, and missing gates according to an explicit policy.
4. Render the measured product with a documented, perceptually ordered color scale appropriate to the quantity.
5. Overlay radar location, requested site label, range rings or distance scale, north arrow when orientation could be ambiguous, and optional geographic context.
6. Put product, site, UTC time, units, sweep or product code, range, and color bar in the figure itself.

For reflectivity, do not imply that every dBZ color boundary is a categorical precipitation type. Keep the measured reflectivity label visible and put any rain-rate relation in a separate, explicitly derived layer.

For velocity, use a diverging scale centered on zero unless the product's documented semantics require another convention. Radial velocity points toward or away from the radar according to the data convention; it is not a full wind vector. Do not draw environmental wind arrows from radial velocity without an explicit deconvolution or retrieval method.

Plot Dual-Polarization Moments

Preserve the physical unit for each field, such as differential reflectivity in dB, differential phase in degrees, correlation coefficient as a unitless quantity, and specific differential phase with its documented units and scale.

Keep raw dual-polarization fields separate from hydrometeor classification. If a classification is displayed, state the input moments, thresholds, quality masking, and whether the classification is measured, retrieved, or heuristic.

Do not normalize each sweep independently before an animation or comparison; that can make a changing storm look stationary. Use one declared scale for the whole sequence unless a separate panel is explicitly labeled.

Choose a Sweep for a Target

Lowest-level products emphasize near-surface structure but are vulnerable to terrain, clutter, biological targets, and beam broadening. Higher sweeps sample different heights and can miss low-level features.

When selecting a sweep by target height:

1. use the radar elevation angles and a documented beam-height relationship;
2. solve for the nearest sweep at the requested range and height;
3. label the selected elevation and estimated sampling height;
4. show the choice on a vertical cross-section when the selection is material.

Do not call the lowest sweep a surface observation. Its beam samples a volume whose center height varies with range and whose width increases away from the radar.

Plot RHI, Cross-Sections, and Tilts

An RHI or cross-section is a derived view assembled from multiple sweeps or volumes. Preserve source volume identity, azimuth or line orientation, horizontal-distance coordinate, vertical coordinate, interpolation method, and beam-height geometry.

Do not connect gates across large angular gaps, missing sweeps, or incompatible volumes without showing the gap. Avoid implying sub-beam vertical resolution. For a storm tilt sequence, use the same cross-section line or documented tracking logic across times and show how the line moves.

Create Time Sequences

For an animation or loop:

• use a verified chronological scan sequence;
• preserve the requested cadence and mark skipped or duplicated scans;
• keep site, product, color scale, map bounds, and range constant;
• show UTC time on every frame or in a clearly visible persistent timestamp;
• do not duplicate a stale frame to fill a gap without labeling the hold;
• stop at the last verified frame when the stream ends.

An animation is not evidence of temporal evolution unless frames are aligned, correctly timed, and generated from the same product and projection.

Plot a Precomputed Mosaic

For an MRMS or other decoded NEXRAD-derived grid:

1. Verify product identity, domain, valid or accumulation time, units, grid projection, dimensions, coordinate orientation, and decoded extent.
2. Apply the product's scale, offset, fill values, quality flags, and coverage mask before rendering. Preserve missing coverage as missing; do not turn it into zero-valued precipitation or reflectivity.
3. Render the documented geographic extent and coordinate grid. Reproject only with an explicit transformation and retain the native grid metadata.
4. Label the exact product, provider, domain, valid-time interval, units, and color scale. Show coverage or source attribution when supplied with the decoded data.
5. Keep official provider products distinct from locally constructed mosaics; use nexrad-mosaic-construction for construction and label its output as a local analysis.

Do not apply single-radar azimuth/range geometry or sweep labels to an MRMS grid. Do not claim a mosaic represents every native radar moment or elevation.