January 26, 2026
Karl vs Claude
Show HN: SF Microclimates
New SF microclimate API sparks fog wars: PurpleAir fans, Wunderground skeptics, and “just tell me what to wear” crowd
TLDR: A free API now reports real temps for 50 SF neighborhoods using PurpleAir sensors. Commenters spar over using PurpleAir’s own map, ask if it’s Wunderground data, demand a human-friendly page, and argue about Celsius—highlighting a split between dev tools and “tell me what to wear” simplicity.
San Franciscans just got a free, no‑signup API that claims real neighborhood weather—because “San Francisco: 58°F” means nothing when the Mission is sunny at 65 while the Outer Sunset is a fog fridge at 52. Solo Founders’ SF Microclimates aggregates 150+ PurpleAir sensors, serves 50 neighborhoods, and proudly says: curl it, bot it, or self‑host it.
Cue the community drama. One camp immediately pointed to the source and said, “just use PurpleAir’s map,” flexing thousands of dots and shade‑versus‑sun nuance. Another grilled the provenance—“Is this Wunderground?”—while data nerds asked for raw sensor access, not just neighborhood averages. Then the fashion-forward crowd crashed the party: why is there no human-readable page telling them what jacket to wear right now? And of course, the metric brigade showed up asking for Celsius, because we can’t have nice things without an imperial vs metric skirmish.
The vibes: Karl the Fog meets Claude the Bot. Devs love the agent-ready endpoints; everyday residents want a simple, colorful dashboard and “Mission vs Sunset” at a glance. It’s practical, it’s nerdy, it’s peak SF—half the thread debating data sources, half dunking on airport temps, and everyone agreeing on one thing: microclimates are real, and layers are life.
Key Points
- •SF Microclimates is a free, no‑key API delivering real-time weather for 50 San Francisco neighborhoods.
- •It aggregates data from 150+ PurpleAir outdoor sensors and groups them by neighborhood to compute averages.
- •Endpoints include all neighborhoods, single neighborhood, and a list of available neighborhoods, returning JSON with temp, humidity, and sensor count.
- •Self-hosting uses a GitHub repo, a PurpleAir API key, Cloudflare KV (via Wrangler), environment secrets, and wrangler deploy.
- •Caching (default 1 hour) and rate limiting are implemented; data is fetched on cache miss and returned with CORS headers.