Measured against the sky
The w* smoke correction in Smoke and thermals runs on constants I’d cited from papers but never checked against a real sky. The August 2026 BC smoke event was the first chance: GOES-18 measuring, from orbit, the same sky the forecast models describe.
Measured irradiance
The engine’s catalogue carries GOES-18’s satellite-measured downward
shortwave as an observation model (goes18-dsr), publishing ten-minute
observation documents for
whatever sites an operator serves. On the capability’s first live day,
the four sites I serve read 554–623 W/m², all quality-good, in one
smoky late morning [observed 2026-08-10]. That
fits: a cloudless sky delivers ~650–700 W/m², and the plume overhead
took the rest. Measured irradiance beside a smoke document’s optical
depth is exactly the comparison exp(−0.16·τ) was fitted from. Any
operator publishing both datasets keeps that comparison running.
The third opinion: measured smoke
The optical depth itself is measured too. GOES-18’s aerosol optical
depth is the catalogue’s second observation model (goes18-aod), so a
Meteogram can hold three independent statements about the same smoke
side by side: RAQDPS’s forecast AOT, HRRR’s physics-felt smoke, and
GOES-18’s measured AOT. Same quantity, same 550 nm wavelength, same
field name. They draw as neighbouring strips with one haze encoding:
the measured strip’s tint is the forecast smoke strip’s own, so one key
chip explains both and the eye compares them directly. Like every
measurement, the strip renders below the provenance divider. Its gaps
carry meaning: it is a daytime product, and an absent instant means no
accepted retrieval, never clear air.
Agreement between the forecast smoke strip and the measured strip is earned trust: the plume the smoke-adjusted view derates w* with is really overhead, at about the stated thickness. Disagreement is the more valuable signal. It means the forecast plume is misplaced, mistimed, or mis-sized, and the adjusted view inherits that error, so read its derated thermals with the same skepticism. The measurement is authoritative for right now; only a forecast covers the hours ahead. I watched the measured strip’s first live afternoon (the same BC event) track the plume over one of the four sites, thinning from AOT 3.0 to 1.4 in under two hours [observed 2026-08-10] — finally, a number the forecast strips beside it can be held to.
The stamped observations re-ran from the append-only observation
history of the reference operator,
azohra/acrophobia-forecasts:
the goes18-dsr/history/<site>/2026-08.jsonl.gz month archive and its
goes18-aod twin, private data. The
sample dataset
publishes the same month-archive convention, though its archives hold
forecast profiles; no observation documents ship in the sample.