Plot Description:

This autoplot attempts to estimate the number of people or area in the US under a given NWS Watch/Warning/Advisory (WaWA). Double-accounting is somewhat a problem here in the case of overlapping polygons. For each WaWA type, if there are polygons associated with the event, the population of the polygon intersection with the 30 arc-second grid is used.

While the graphic only displays the top 10, the data download provides everything available to be computed.

Footnote on "Active" WaWA: A more complex than it should be nuance to explain here is the concept of what is "active" at a given timestamp. Let us consider a real world example. On Monday afternoon, the NWS issues a Winter Storm Warning for an upcoming storm that goes "into effect" at noon on Tuesday. You request this plot for a timestamp of 6 PM on that Monday. Is the Winter Storm Warning included in this metric at that time?

• Yes, if you select the option to include any WaWA that have been created, but may have an VTEC start time in the future yet.
• No, if you select the option to only include WaWA that have an issuance time before the given timestamp.

The default setting here is the first option, to include any events that have been created, but not necessarily having an issuance time prior to the given timestamp. This is why we can't have nice things!

Autoplot 247 is closely related to this app and provides a map of WaWa + stats.