Nexrad Product Access

NEXRAD Product Access

Overview

Select and retrieve the correct NEXRAD data for one radar site, UTC time, and requested product or Level II moment. Keep archive volumes, real-time chunks, and Level III products distinct because they have different availability and decoding contracts.

Use noaa-radar-satellite-fetching for common NOAA archive discovery and download mechanics when that skill is available. This skill provides the NEXRAD-specific Level II/III selection contract. Use nexrad-mosaic-access when the requested result is a precomputed multi-radar composite rather than one site's data.

When to Use This Skill

• Fetch a completed NEXRAD Level II volume from the historical archive.
• Follow or assemble real-time Level II chunks for a named site.
• Retrieve selected real-time Level III products or use an operational Level III feed.
• Select a product such as reflectivity, velocity, spectrum width, echo top, vertically integrated liquid, or a supported dual-polarization product.
• Select a particular Level II moment, elevation sweep, or volume interval.
• Restrict access to one radar site and reject composite or neighboring-site data.

Do not turn a Level II moment name into a Level III product code by assumption. The two levels have different processing and distribution contracts.

Current Public NEXRAD Resources

The current NEXRAD-on-AWS registry documents these public resources in us-east-1:

Unidata documentation also describes operational Level III distribution through the NEXRAD3 LDM/NOAAPort feed. Resolve the current source for the requested Level III product instead of assuming that a real-time S3 bucket is a complete archive.

The current AWS registry identifies unidata-nexrad-level2 as the archive and says the former noaa-nexrad-level2 bucket was deprecated after September 1, 2025. Verify the live registry before access because provider resources can change.

Define the Access Contract

Resolve and record:

• one four-character NEXRAD site such as KTLX;
• the requested instant or bounded interval in UTC;
• nearest-at-or-before, nearest-in-either-direction, or interval-overlap policy;
• data level: Level II, Level III, or an explicitly mixed workflow;
• product or moment, unit, sweep or scan angle, and whether all sweeps or the lowest requested sweep are needed;
• archive, real-time, or operational-feed source;
• maximum lookback, maximum probes, and acceptable latency;
• required metadata, quality masks, and output form;
• whether the product must come from that one site only.

If the user supplies only a display concept such as “base reflectivity,” resolve it against a current official product or Level II moment definition. Do not guess a Level III code or claim that every named display is available in the same feed.

Access Historical Level II Volumes

1. Validate the site against an allowlist or a current NEXRAD site inventory.
2. Resolve the exact UTC day and site prefix from current dataset documentation. Do not infer the key layout from a filename example.
3. List only that documented prefix, paginating within a bounded key count.
4. Parse the documented volume timestamp and site from each candidate key.
5. Select by the time policy, then request metadata for the exact key.
6. Require a nonzero stable object. If publication may still be occurring, repeat the metadata check until size and object identity remain unchanged.
7. Download to a temporary path, verify received bytes, compute a local SHA-256 when provenance requires it, and open with a format-aware reader.
8. Verify the decoded site, volume start/end time, sweeps, moments, dimensions, and quality fields before promoting the file into a valid cache entry.

The archive is the preferred source for retrospective work because each object is a completed volume. Do not substitute a real-time chunk for an archive volume when the consumer expects a self-contained volume.

Access Real-Time Level II Chunks

Treat each chunk as a fragment with ordering and completion dependencies.

1. Resolve the current chunk prefix for the requested site.
2. Parse volume and chunk identity from documented key fields.
3. Discover the complete chunk sequence with a bounded lookback.
4. Verify required chunks, byte identities, and scan metadata.
5. Assemble into a new temporary file without overwriting the source chunks.
6. Decode the assembled object and verify site, volume time, sweep count, moments, and quality fields.
7. Publish the verified volume atomically and record which chunks formed it.

If a chunk is late, duplicated, discontinuous, or from another site, reject or quarantine the sequence. A file that opens without proving complete volume metadata is not a verified replacement for an archive volume.

Select Level II Moments and Sweeps

Level II exposes moments within a volume rather than independent Level III display products. Depending on the radar configuration and volume, common moments can include reflectivity, velocity, spectrum width, and supported dual-polarization quantities.

Before extraction, record:

• the exact moment name used by the decoded file;
• its calibrated physical unit and scale or offset;
• the elevation-angle policy and actual beam height at the display range;
• the quality fields for range folding, clutter, dealiasing, or invalid gates;
• whether the output requires all sweeps, a nearest sweep, or a sweep search based on target height.

Do not assume that a moment is present in every volume or at every sweep. Report an absent moment or incomplete sweep rather than converting a different moment into its place.