• any event that causes death or injury is included in the event database;

  • any event that causes crop or property damage in excess of $500,000 is included in the event database;

  • an event is not considered a duplicate if it is the only event verifying a warning.

Any event not recorded in the verification database due to the aforementioned duplicate rule still appears in the publication Storm Data.

Warnings and events are recorded in separate databases. Whenever an event occurs in a warned county, the following are recorded: one verified warning and one warned event. One unwarned event is recorded for each event that occurs in a county with no warning. One unverified warning is counted for each warned county that does not experience an event.

Quality Assurance Rules

In an attempt to reduce the impact of erroneous short-fused warnings on customers and, at the same time, more accurately measure the quality of NWS warnings, the OCWWS Performance Branch has developed a set of rules stating how these short-fused warnings are archived.

  • Rule 1: How Warnings are Entered into the Database. All data imported into the warning database are taken directly from the warning. No data are entered into the database from any information other than that represented by the bold-faced parts of the warning sample in Table D.1. Based on this rule, products issued with the improper coding may or may not be imported into the database. Several examples appear on the NWS Verification Web Page.

  • Rule 2: Quality Assurance of Overlapping Warnings. When two warnings for a given county overlap in time, the portion of the earlier warning that overlaps the second warning is removed. The expiration time of the first warning is changed to one minute before the issuance time of the second warning. Several examples appear on the NWS Verification Web Page.

Lead Time

For verification purposes, the definition of the term “event” is given above. The lead time for each flash flood event is computed separately for each county by subtracting the time of warning issuance from the time



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