Is Mount Tam Cloudy? — Webcam Overcast Check

Purpose

Decide whether Mount Tamalpais (Marin County, CA) is currently overcast by visually inspecting the live webcam feed published on rntl.net/mt-tam-cam-tamalpais-webcam. Returns a categorical sky condition (clear / partly_cloudy / overcast / fogged_in / night_unreadable), a go_recommendation (boolean — go vs. don't go for a view-quality hike), the captured camera timestamp, and the snapshot URL. Read-only; never posts, never controls the camera, never books anything.

When to Use

• "Should I drive up to East Peak / Rock Spring / Pantoll today, or will I be inside a cloud?"
• A morning briefing agent assembling weather context for Bay Area outdoor plans.
• A trail-condition aggregator pairing this signal with NWS forecasts and AQI for Marin County.
• Anywhere the question is "is the sky clear right now over Mt. Tam" answered from real-time imagery, not a forecast.

Workflow

The rntl.net page is a long WordPress index of Bay Area webcams; its primary "Mt. Tam Cam" iframe is an ipcamlive.com player (the Sigward / Muir Beach camera facing south across the southwestern flank of Mt. Tam toward Sutro Tower and Ocean Beach). The optimal path bypasses both rntl.net and the JS-heavy iframe player and pulls the still JPEG directly from ipcamlive.com's snapshot endpoint, then hands the image to a multimodal model for sky classification. This is ~50× cheaper than driving the page in a headless browser and avoids the WebSocket/HLS streaming pipeline entirely.

1. Resolve the camera alias. The primary Mt. Tam Cam alias is 608dc4709bc06 (Sigward / Muir Beach, south-facing — the headline camera on the rntl.net page). A secondary bay-facing cam alias 5e863c6e0e66d is also embedded on the same page and can be used as a cross-check. If you need to re-discover or verify the alias, do one cheap HTTP fetch of the page and grep for ipcamlive.com/player/player.php?alias=([a-f0-9]+) — the first match is the headline cam. No browser session is needed.

   ALIAS=608dc4709bc06          # Sigward / Muir Beach – primary
   ALIAS_SECONDARY=5e863c6e0e66d # Bay-facing cross-check cam
   

2. Pull the snapshot JPEG. The ipcamlive snapshot endpoint issues a 302 to a per-stream snapshot.jpg on a numbered edge host (s73.ipcamlive.com at time of writing — do not hardcode; follow the redirect). The JPEG is served with Access-Control-Allow-Origin: *, Cache-Control: no-cache, and a Last-Modified header that is the exact capture timestamp of the still. Use a residential-proxy HTTP fetch (browse cloud fetch --proxies) — no Browserbase browser session is required.

   browse cloud fetch "https://g1.ipcamlive.com/player/snapshot.php?alias=$ALIAS" --proxies
   # → 302 Location: https://s73.ipcamlive.com/streams/<streamId>/snapshot.jpg
   browse cloud fetch "https://s73.ipcamlive.com/streams/<streamId>/snapshot.jpg" --proxies
   # → 200, content-type: image/jpeg, body is base64 in the fetch envelope's `content` field
   

   Decode the base64 content to bytes; the result is a ~1280×720 JPEG ≈ 25–135 KB.

3. Read the burned-in timestamp. The primary Sigward cam stamps the frame in its bottom-left corner as YYYY-MM-DD HH:MM:SS <DayName> in Pacific time. Cross-check it against the response's Last-Modified header to confirm the stream is live (not a stale image). If the two differ by more than ~5 minutes, treat the feed as stale and either retry after 60 s or fail soft with night_unreadable / feed_stale.

4. Visually classify the sky. Pass the JPEG to a multimodal model with a structured prompt:

   "Look at the upper third of this Mt. Tam / Marin coast webcam image. Classify the sky as exactly one of: clear (mostly blue, < 25% cloud cover), partly_cloudy (25–75% cloud cover or scattered clouds), overcast (> 75% uniform gray cloud cover or low ceiling obscuring distant ridgelines), fogged_in (camera lens is in cloud — distant features invisible, image is mostly uniform gray), or night_unreadable (frame is too dark to judge). Also report whether distant ridgelines / Sutro Tower across the bay are visible. Respond as JSON: {condition, ridgelines_visible: boolean, notes: string}."

   Apply the decision rule: go_recommendation = condition ∈ {clear, partly_cloudy} AND ridgelines_visible === true. Both overcast and fogged_in should map to go_recommendation: false. night_unreadable should set go_recommendation: null and explain that the feed cannot be visually judged at this hour — defer to a forecast.

5. (Optional) Cross-check with the secondary cam. When the answer is borderline (partly_cloudy with ambiguous ridgeline visibility) or when the primary cam's last-modified is stale, repeat steps 2–4 with ALIAS_SECONDARY=5e863c6e0e66d and reconcile. Disagreement between the two cams (one clear, one fogged) usually means a low marine layer along the coast — flag this as notes: "marine_layer_likely" and lean toward partly_cloudy.

Browser fallback

Only use this if ipcamlive.com is unreachable or the snapshot endpoint stops responding (no observed instances as of 2026-05-18):

SID=$(browse cloud sessions create --keep-alive --proxies --verified | jq -r .id)
browse open "https://www.rntl.net/mt-tam-cam-tamalpais-webcam/" --remote --session "$SID"
browse wait load --remote --session "$SID"
browse wait timeout 4000 --remote --session "$SID"   # iframe player streams in
browse screenshot --remote --session "$SID" --path /tmp/mt-tam.png
browse cloud sessions update "$SID" --status REQUEST_RELEASE

Then hand /tmp/mt-tam.png to the same multimodal classifier from step 4. This costs roughly two orders of magnitude more (Browserbase session + proxy minutes) and the resulting image is a screenshot of a player UI, not the raw camera frame — accuracy suffers because the player overlays controls. Prefer the API path.

Site-Specific Gotchas

• The "Mt. Tam Cam" branding is misleading. The headline iframe on rntl.net/mt-tam-cam-tamalpais-webcam is the Sigward Muir Beach cam (608dc4709bc06) — it points south from the Muir Beach headlands toward Sutro Tower and Ocean Beach, not up at the Mt. Tam summit. It is a valid proxy for "is the western Marin coast under marine layer / overcast today?" but it is not a summit cam. The image's burned-in caption confirms this: "Muir Beach www.sigward.com — Webcamera facing south to Sutro Tower and Ocean Beach in San Francisco west of Golden Gate". Document this in the user-facing output as vantage: "Muir Beach S-facing" so the consumer doesn't assume summit conditions.
• Snapshot endpoint = 302 redirect; follow it. GET https://g1.ipcamlive.com/player/snapshot.php?alias=<ALIAS> returns 302 Location: https://s<N>.ipcamlive.com/streams/<streamId>/snapshot.jpg. The numbered edge host (s73, s74, …) is not stable across cameras and may rebalance over time — always follow the redirect, never hardcode the edge.
• No auth, no cookies, no anti-bot. Both rntl.net (Cloudflare front, served DYNAMIC cache status) and ipcamlive.com (Apache, no challenge) accept proxy fetches with no friction. --verified stealth is unnecessary for the snapshot path; --proxies alone is sufficient. The browser fallback uses --verified --proxies purely for resilience against the multi-iframe page.
• Last-Modified vs. burned-in timestamp. The response's Last-Modified header is roughly accurate to the second the snapshot was generated server-side, but the timestamp burned into the frame (bottom-left, white text) is the camera's own clock and is the authoritative capture time. Use the burned-in time for user-facing display.
• Snapshot refresh cadence ≈ 30–60 seconds. Repeated polls within ~30 seconds return the same JPEG (same Etag). If you need a truly fresh frame, space requests ≥ 60 s apart.
• Night frames are mostly unreadable. The Sigward cam is not IR-equipped — after sunset (roughly 19:30–06:30 PT depending on season) frames go nearly black except for a few Marin/SF light points. Don't attempt overcast classification at night; return night_unreadable and defer to NWS marine forecast (weather.gov/mtr). The secondary cam (5e863c6e0e66d) is similarly dark at night.
• Marine layer ≠ overcast for hiking decisions. A common Bay Area pattern is a low marine layer sitting on the coast (Muir Beach fogged in) while Mt. Tam's summit (~2,571 ft) is in clear sun above it. If the primary cam shows uniform gray with invisible distant ridgelines but the secondary bay-facing cam is clear, the summit may still be a great destination above the inversion. Surface this as notes: "marine_layer_likely_summit_may_be_above" rather than a flat "don't go".
• Page is a giant index of cams, not a single cam. rntl.net/mt-tam-cam-tamalpais-webcam embeds 10+ iframes including YouTube live streams (FLoSUN_Vrz4, CO4lgqL7Fhg), CBS Salesforce Tower cams, Ventusky wind embed, and a boardsportscalifornia.com/coyotecam.jpg still. The two ipcamlive.com iframes (608dc4709bc06 and 5e863c6e0e66d) are the only ones with a documented public snapshot endpoint; the YouTube embeds would require frame extraction via streamlink/yt-dlp and are not worth the cost.
• JPEG carries no EXIF. Don't try to read GPS / timestamp metadata from the JPEG bytes — the camera strips it. The burned-in caption and the response headers are the only metadata channels.
• Browserbase WebSocket connect (connect.usw2.browserbase.com) is reachable from the agent sandbox via the SDK proxy but not via raw DNS. This is why the recommended path uses browse cloud fetch (Browserbase Fetch API, HTTPS-only) rather than browse open --remote (CDP over WSS). If you do need the browser fallback, ensure your environment supports the Browserbase connect URL — local-mode browse without --remote will not have residential proxying.

Expected Output

Five distinct outcome shapes — return exactly one:

// Clear or partly cloudy — go
{
  "condition": "clear",
  "ridgelines_visible": true,
  "go_recommendation": true,
  "captured_at": "2026-05-18T15:33:13-07:00",
  "captured_at_source": "burned_in_timestamp",
  "vantage": "Muir Beach S-facing (Sigward cam)",
  "snapshot_url": "https://s73.ipcamlive.com/streams/49vri5j7owhgsudrs/snapshot.jpg",
  "alias": "608dc4709bc06",
  "notes": "Blue sky with light horizon haze."
}

// Overcast — don't go for views
{
  "condition": "overcast",
  "ridgelines_visible": false,
  "go_recommendation": false,
  "captured_at": "2026-05-18T07:12:00-07:00",
  "captured_at_source": "burned_in_timestamp",
  "vantage": "Muir Beach S-facing (Sigward cam)",
  "snapshot_url": "https://s73.ipcamlive.com/streams/49vri5j7owhgsudrs/snapshot.jpg",
  "alias": "608dc4709bc06",
  "notes": "Uniform gray sky, distant ridges invisible."
}

// Fogged in at the coast — summit may be above the marine layer
{
  "condition": "fogged_in",
  "ridgelines_visible": false,
  "go_recommendation": false,
  "captured_at": "2026-05-18T08:45:00-07:00",
  "captured_at_source": "burned_in_timestamp",
  "vantage": "Muir Beach S-facing (Sigward cam)",
  "snapshot_url": "https://s73.ipcamlive.com/streams/49vri5j7owhgsudrs/snapshot.jpg",
  "alias": "608dc4709bc06",
  "notes": "marine_layer_likely_summit_may_be_above — cross-check secondary cam (5e863c6e0e66d) and consider East Peak which often sits above the inversion."
}

// Night — defer
{
  "condition": "night_unreadable",
  "ridgelines_visible": null,
  "go_recommendation": null,
  "captured_at": "2026-05-18T22:33:00-07:00",
  "captured_at_source": "burned_in_timestamp",
  "vantage": "Muir Beach S-facing (Sigward cam)",
  "snapshot_url": "https://s73.ipcamlive.com/streams/49vri5j7owhgsudrs/snapshot.jpg",
  "alias": "608dc4709bc06",
  "notes": "Frame too dark for visual classification — defer to weather.gov/mtr forecast."
}

// Feed stale / unreachable
{
  "condition": "feed_stale",
  "ridgelines_visible": null,
  "go_recommendation": null,
  "captured_at": "2026-05-18T03:00:00-07:00",
  "captured_at_source": "burned_in_timestamp",
  "vantage": "Muir Beach S-facing (Sigward cam)",
  "snapshot_url": "https://s73.ipcamlive.com/streams/49vri5j7owhgsudrs/snapshot.jpg",
  "alias": "608dc4709bc06",
  "notes": "Last-Modified header > 1 hour ago; image likely stale. Retried 60 s later, same Etag — try secondary cam or fall back to forecast."
}