What is the whistle at noon?

Katharine K sent in a question and asked if we could find the answer:

I was born and raised on 20th Ave in Shoreline, near the South Woods, and I have a question about a neighborhood curiosity that I was hoping someone could answer. As long as I can remember, every Wednesday at noon, there is a loud horn/train whistle/siren that blasts a few times. All I can think is that it is some emergency warning system that is tested each week, but no one I talk to has any clue what it is. It seems to be coming from the direction of Hamlin park or Fircrest.

For this, we went to Patricia Hale, who knows All Things Ridgecrest. We thought she might have some information from across the street in Briarcrest, and she did:

Harkens back to the days of the Civil Air Patrol - and the Early Warning system for Disasters.  

When I was growing up in Walla Walla - (number of years ago will not be disclosed)

we had a siren located a few blocks from our grade school that ran a test every Wednesday at noon. 

Kind of like the current day "this is a test, if there would have been a real emergency, you would have been instructed...." 

What we hear locally emanates from the Fircrest property. The buildings there are heated with steam from the plant located right there on the grounds. The noise is a Steam Whistle that is tested every Wednesday at noon. 

It is a hold-over from the Navy Hospital which was located there during the War years from 1942-47. They would have had the steam whistle as part of their warning system in case of attack. 

If you ever hear the whistle at any time other than Wednesday at noon, I suggest you duck, cover and hold!

Thanks to Katharine for the great question and Patty for the informative answer!