What happened, next to what was modeled

Calchis draws modeled zones around a live event the moment it arrives: consequence rings for an earthquake, wind zones for a hurricane, the warning polygon for a flood. They are estimates, and they say so. After an event, the federal agencies publish what actually happened. Calchis keeps those measured footprints separately and shows them beside the model, so the two can be compared and never confused.

What is collected

NWS damage surveys. After a tornado or damaging wind, Weather Service teams survey the damage and publish each path, its Enhanced Fujita rating, width, length, start time and any deaths or injuries in the Damage Assessment Toolkit. Calchis collects the tracks, damage points and rated polygons and links each one to the nearest warning by place and time.

USGS ShakeMap. For significant earthquakes, USGS publishes contours of the shaking felt, in Modified Mercalli intensity. Its contours are stored as the event's measured shaking, and when ShakeMap is published within three days of an earthquake, the earthquake's modeled rings are rebuilt from it.

NHC's final wind swath. After a hurricane, the National Hurricane Center's best track gives the area that actually saw tropical-storm, 50-knot and hurricane-force winds. Calchis stores it for Atlantic storms, and for Pacific storms whose swath reaches US territory.

USGS high-water marks. After a flood or a surge, USGS field crews flag and survey how high the water reached, mark by mark. Each one carries its surveyed elevation, its datum and its quality class. Surveyors' names and free-text notes are not stored.

Where to see them

On the map, turn on Observed (NWS/USGS/NHC) in the layer list. Measured footprints are drawn in a cyan no peril, zone or forecast uses, so they cannot be mistaken for a modeled zone. On an event's page, the Observed section lists each one with its source and a link to the agency's own record.

What they are not

Not instant. Surveys and swaths arrive hours to days after an event, and are added as they are published. An event with no measured footprint yet has simply not been surveyed, or not published.

Not a verdict on the model. A measured footprint is the agency's record; the modeled zone was Calchis's estimate at the time. Where they differ, the measured one is what happened.

Not every link is certain. A survey is matched to a Calchis event by place and time, or by the source's own id. A mark that matches nothing is kept and shown as unmatched, never forced onto the nearest event.