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 browserless_function with residential proxy (proxy: { proxy: "residential" }) — no full browserless_agent browsing flow is required.

   Because a browserless_function runs in a browser page context (a bare fetch has no egress until the page navigates), have the page navigate to the snapshot URL itself — page.goto transparently follows the 302 to the numbered edge host, and you can read the final URL, Last-Modified, and bytes off the response:

   export default async ({ page }) => {
     const resp = await page.goto(
       `https://g1.ipcamlive.com/player/snapshot.php?alias=${ALIAS}`,
       { waitUntil: "load", timeout: 45000 },
     );
     const finalUrl = resp.url(); // https://s73.ipcamlive.com/streams/<id>/snapshot.jpg
     const lastModified = resp.headers()["last-modified"];
     const buf = await resp.body(); // JPEG bytes, ~1280×720 ≈ 25–135 KB
     return { data: buf, type: "image/jpeg" }; // proper binary block — never a multi-hundred-KB base64 text return
   };

   Return the image as a proper binary block ({ data, type: "image/jpeg" }), or just surface finalUrl so a downstream vision model can fetch it — don't ship raw base64 back as text.

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):

A single browserless_agent call (residential proxy), all commands in one call so the session persists:

{ "method": "goto", "params": { "url": "https://www.rntl.net/mt-tam-cam-tamalpais-webcam/", "waitUntil": "load", "timeout": 45000 } }
{ "method": "waitForTimeout", "params": { "time": 4000 } }
{ "method": "screenshot" }

No session-release step — there is nothing to release (the session actually persists across calls, keyed by its proxy/profile config; it does not die on return). Then hand the returned screenshot to the same multimodal classifier from step 4. This costs roughly two orders of magnitude more (a full browser session + proxy) 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. No stealth/anti-bot handling is needed for the snapshot path; a residential proxy alone is sufficient. The browser fallback uses a residential-proxy browserless_agent session 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.
• Prefer the lightweight function fetch over a full browsing session. The recommended path uses a browserless_function (image fetch) rather than a full browserless_agent browsing flow because it's far cheaper and avoids the iframe/HLS pipeline entirely. Reach for browserless_agent only for the screenshot fallback, and always pass proxy: { proxy: "residential" } on it so the egress is residential.

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."
}