Each alert carries a CAP severity and a VTEC significance. Color and rank by
significance: it is the axis the NWS asks people to read. CAP severity is too
coarse to sort on. A Tornado Warning, a Flood Warning and a Winter Storm Watch
can all be Severe, plenty of warnings are only Moderate, and a Special
Weather Statement is Moderate too, which is not a watch.
significance |
Meaning |
|---|---|
W |
Warning: occurring or imminent |
A |
Watch: conditions favourable |
Y |
Advisory: less serious |
S |
Statement |
significance and phenomena are null on products with no VTEC, chiefly
Special Weather Statements and Marine Weather Statements. Fall back to CAP
severity for those (Extreme reads as a warning, Severe as a watch,
Moderate as an advisory), which is what the API’s own ranking does.
The ranking
Routes that return alerts “most serious first” sort by significance, then by
hazard (tornado and tsunami, then storm surge, then flash flood, severe
thunderstorm and hurricane, down through winter, fire and flood to marine and
beach hazards), then by CAP urgency, then newest. A Flood Warning outranks a
Tornado Watch on purpose: a warning is something happening.
The fields involved are described on the alerts reference,
for example under GET /alerts/highest-severity.