What Chaseit actually runsAnd what each piece does for the chase

1 — Forecasting · what might happen

A chase day starts two to four days out. You are trying to work out whether anything is on at all, and if so where the corridor sits. Four surfaces do the heavy lifting here, and they are all public.

The convective outlook is our headline. The Stormfront lens compiles CAPE, shear, helicity, LPI and jet streaks from Open-Meteo and Met Office UKV into a 5-day categorical risk surface — NONE, MRGL, SLGT, ENH, MDT and HIGH. It is the same vocabulary as the SPC and ESTOFEX, applied to UK ingredients, and it is what we anchor a chase-day call on. The headline cards on the outlook page are computed; the risk surface underneath is regional.

Once a day is interesting, soundings is where you time it. Hourly CAPE, shear and LPI across twelve forecast points covering southern England, the Midlands, Wales and East Anglia. It is derived from open-meteo and it tells you when the cap breaks and how long the window stays open.

Then the wind atlas. This one is unusual. UK upper-air winds derived live from ADS-B Mode-S EHS reports — aircraft transponders broadcasting wind speed and direction at flight level as they cross the country. Every tile gets a vertical profile, a hodograph, a 0–6 km shear figure and a chase score. Nobody else exposes this for chasers in this form. It exists because the official radiosonde network in the UK is sparse and stops in places that matter to us, and because the aircraft data is already in the sky and free.

Last of the forecasting tools, the chase targets page. Composite of CAPE times shear times jet, ranked, marker by marker on a map. Tap a marker for the headline; scroll for the full per-target detail. It is opinionated on purpose — the point is to argue with it.

2 — Nowcasting · what is happening

On the day itself, the forecast tools step back and two live surfaces take over.

The radar composite page is the Met Office composite at a 5-minute refresh over a southern UK domain, with a Blitzortung lightning overlay on the same map. It is the surface that gets left open in a browser tab for the duration of a chase.

Behind the lightning overlay there is also a direct EUMETSAT MTG-LI ingest — the Lightning Imager on the new Meteosat Third Generation satellite. It is not relayed from a third-party network; we pull granules from EUMETSAT and cache them ourselves. That matters mostly when the terrestrial detection networks have gaps or lag, which is more often than you might think.

3 — Reports + verification · what just happened

The chase is over. Now the work shifts to logging it.

The public reports feed is the front door — tornado, funnel, hail, wind, lightning, flood and structural impact reports submitted by chasers, geotagged, with photos. Each report has its own page with the full media gallery and the time and place pinned.

The storm log is the member back-office for the same data. Submit, search, filter and export. Each report has a public-visibility toggle, so chasers who want their report on the public feed can flip it; the rest stays private. Exports are CSV in ESSL/ESWD format — the European Severe Weather Database schema — so reports can flow into the European archive without further transformation.

Verification is the bit that makes the reports useful to anyone else. Every report is matched against Met Office warning snapshots taken at the time of the event. A verified tag means a real warning was active at that place and time when the report was submitted. It is not a quality judgement on the chaser; it is a cross-check against the official record.

4 — Community + comms · doing it together

The forecasting tools are the headline, but the reason the site exists is the group of people running them.

News collects event recaps, season notes, kit reviews and announcements. Each post can anchor to a specific outlook day and a cluster of reports, so the recap stitches the forecast context back to what actually verified. The events calendar holds chase days, briefings, training and meetups; members RSVP. And the chasers directory is the public roster, with a season-tally leaderboard ranked by public reports submitted in the last twelve months.

For people who would rather not refresh the site, there are email digests — daily outlook, severe-day alerts, news and event announcements, and per-region SLGT-and-above pings. Approved members set their topic and region preferences from their profile. Everything is double opt-in and there is a one-click unsubscribe on every message.

For tooling, an RSS feed covers reports and news. An ICS calendar feed covers events — point Apple Calendar, Google Calendar or Outlook at it and the chase calendar appears alongside everything else.

5 — The plumbing · what you do not see

All of the consumer-facing surfaces above are powered by a small stack of internal services. You do not need to know any of this to use the site, but it explains why things work the way they do when something is occasionally slow or stale.

Siphon is the data ingest engine. It is what talks to radar, lightning, soundings, ADS-B, Met Office warnings and the news sources, and it writes everything into a shared cache keyed by source. It runs on a schedule with per-host throttling so we are well-behaved to upstream providers, and it backs off when a source rate-limits us. Every source has a stable cache key, so the rest of the stack never has to know where the data came from.

Prism is the lens and cache layer. It reads from the siphon cache, runs derived computations on top — the Stormfront convective outlook, wind-atlas tile scoring, target ranking — and exposes the results as consumable endpoints. Chaseit is a Prism consumer. Prism is also what powers live.wispayr.online.

Dispatch is the comms and notifications service. The daily outlook digest, the severe-day alerts, the per-region SLGT-and-above pings — all of those originate in dispatch and go out from a single fanout.

Finally, the historical-storms archive is a curated back-office table of named UK storms, joinable to ICEYE SAR scenes for post-event imagery. It is the long-memory half of the project — the thing that turns a season of reports into something you can look back at in five years.

6 — Where the data comes from

Radar from the Met Office composite. Lightning from EUMETSAT MTG-LI. Soundings and surface fields from open-meteo. Upper-air winds derived from ADS-B Mode-S EHS. Warnings from the Met Office datapoint. We have a longer write-up of every upstream source on the weather data page, including licences and the bits we are not allowed to republish. If you want the chaser-side glossary of CAPE, shear, BWER, hook echoes and the rest, the forecaster wiki has an at-a-glance line per term and a deep dive underneath.

7 — Open source, open data, volunteer-built

Chaseit reads from open data wherever possible. The forecasting tools sit on top of Open-Meteo, Met Office open APIs and EUMETSAT feeds; the upper-air winds come from publicly broadcast aircraft transponders; warnings are the official Met Office record. We do not on-sell any of it. The tools are volunteer-built and run on a small footprint of servers; if you are sceptical of any of the derived numbers, they are derived from sources you can verify yourself.

Chaseit is part of the Wispayr stack — the same Siphon, Prism and Dispatch that power live mapping, intel and comms surfaces elsewhere on Wispayr also run this site. If you want the operational side of the community, the about page is the right next click; if you are new to chasing here, chasing in the UK is a useful primer on why the British setup is its own particular kind of awkward, and why tools built for the US plains do not transplant cleanly. That mismatch is most of the reason this stack exists at all.