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

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