Noaa Radar Satellite Fetching

NOAA Radar and Satellite Fetching

Overview

Retrieve NOAA NEXRAD radar and GOES satellite objects from public cloud archives while preserving the product, platform, spatial sector, and scan-time identity. Discover through narrow prefixes, choose by observation time rather than upload time, and validate the downloaded scientific file before use.

This skill covers raw or provider-produced radar and satellite products. It does not retrieve numerical model output or ordinary station observations.

When to Use This Skill

• A task needs NEXRAD Level II archive volumes or real-time chunks.
• A task needs selected NEXRAD Level III products.
• GOES ABI, GLM, or another GOES-R product is needed for a time and region.
• A download must select the nearest completed scan within a tolerance.
• A public S3 key, satellite assignment, radar site, channel, or sector is uncertain or has changed.

Do not activate this skill merely to display a third-party map tile or to answer a general weather question.

Define the Product Contract

For NEXRAD, specify:

• Level II archive, Level II real-time chunks, or a named Level III product;
• four-character radar site, such as KTLX;
• desired scan time in UTC and nearest/previous/next selection policy;
• maximum time tolerance;
• full volume or exact product code;
• raw file retention and decoder.

For GOES, specify:

• physical satellite number or operational role, such as East or West;
• instrument and product level/short name;
• Full Disk, CONUS, Mesoscale 1, or Mesoscale 2 sector where applicable;
• ABI channel or derived product;
• desired scan time in UTC and tolerance;
• calibration form needed, such as radiance or brightness temperature.

Resolve an operational role to a physical satellite using current NOAA documentation at request time. East and West assignments change over a satellite program's lifetime.

Current Public AWS Routes

Consult the AWS Registry of Open Data before hard-coding a bucket. As of this skill's publication:

• NEXRAD Level II archive: s3://unidata-nexrad-level2/
• NEXRAD Level II real-time chunks: s3://unidata-nexrad-level2-chunks/
• selected NEXRAD Level III real-time data: s3://unidata-nexrad-level3/
• GOES imagery and metadata: satellite-specific buckets such as s3://noaa-goes18/ and s3://noaa-goes19/

The former noaa-nexrad-level2 bucket was deprecated and scheduled to become unavailable on September 1, 2025. Do not copy that retired route from old tutorials.

Discover with Narrow Prefixes

NEXRAD Level II archive objects are organized by UTC date and site. GOES objects are organized by product, year, day of year, and hour. List only the smallest prefix that can contain the requested scan.

aws s3 ls --no-sign-request \
  s3://unidata-nexrad-level2/YYYY/MM/DD/KXXX/

aws s3 ls --no-sign-request \
  s3://noaa-goes19/ABI-L2-CMIPC/YYYY/DDD/HH/

Replace every placeholder with a validated value. Include the adjacent hour or UTC day only when the time tolerance crosses that boundary. Paginate listings and bound the total keys inspected.

Use real-time chunk buckets only when the consumer is designed to assemble and validate chunks. Prefer completed archive volumes for ordinary historical or post-event processing.

Select by Scan Time

Object Last-Modified is publication metadata, not the measurement time.

• For NEXRAD, parse the site and scan timestamp from the documented object name, then confirm time and site from the decoded volume header.
• For GOES-R, filenames encode platform plus scan start (s), end (e), and creation (c) timestamps. Select by scan start or interval overlap, not file creation time.
• Default to the closest scan at or before the requested instant for a retrospective view. Allow a future scan only when the caller explicitly asks for nearest-in-either-direction behavior.
• Reject every candidate outside the stated tolerance.
• When sectors overlap, require the requested sector instead of choosing solely by time.

This standard-library helper extracts GOES-R scan timestamps without opening the NetCDF payload:

import re
from datetime import datetime, timezone
from pathlib import PurePosixPath


GOES_TIMES = re.compile(
    r"_s(?P<start>\d{14})_e(?P<end>\d{14})_c(?P<created>\d{14})"
)


def parse_goes_times(object_key):
    match = GOES_TIMES.search(PurePosixPath(object_key).name)
    if not match:
        raise ValueError(f"unrecognized GOES-R filename: {object_key}")

    def parse(value):
        return datetime.strptime(value, "%Y%j%H%M%S%f").replace(
            tzinfo=timezone.utc
        )

    return {name: parse(value) for name, value in match.groupdict().items()}

Treat filename parsing as discovery. After download, verify the corresponding time coverage and platform attributes inside the file.

Download and Validate

1. Record bucket, exact key, size, ETag, and Last-Modified before transfer.
2. Download to a request-owned temporary path. For public buckets, use unsigned S3 access rather than supplying credentials.
3. If the object might still be publishing, require stable metadata or pin a conditional request to the observed object identity.
4. Verify the received byte count and a provider checksum when one is supplied. Otherwise compute and record a local SHA-256 digest.
5. Open the object with an existing format-aware decoder.
6. Verify site/platform, product, scan interval, and expected dimensions or radar sweeps before renaming it into the cache.

Reuse an installed NEXRAD or NetCDF reader. Do not build a binary radar or satellite decoder merely to fetch a file.

Radar-Specific Checks

• Confirm that the radar site is the requested site and was operational at the scan time.
• Treat Level II volumes, real-time chunks, and Level III products as different contracts; they are not interchangeable encodings.
• Verify volume start time, end time when available, sweep count, moments, and elevation angles after decoding.
• Keep range folding, missing gates, quality masks, and velocity ambiguity explicit.
• A radar's nominal coverage radius does not guarantee useful low-level data at a location. Consider distance, beam height, terrain blockage, and outages.