Watches vs. Warnings & The Great Cascadia Quake Anniversary

January 23, 2018

7:00pm Tuesday

Last night, while most of us were asleep on a quiet winter night, a powerful earthquake rumbled underneath the Gulf of Alaska.  It set off Tsunami warnings around the Gulf, and a Tsunami WATCH for the coastline of Oregon & Washington.  That watch was in effect from around 1:30 to 4:30am…again, while most of us were asleep.

There was a bit of confusion about this so let’s make sure we’re all on the same page with WATCHES vs. WARNINGS.  I think this graphic sums it up well.

Weather Watch vs Warnings

This applies to ALL weather events (snow, wind, ice, flooding, heat) AND Tsunamis as well.

So how about the case of the Tsunami watch this morning?  If it happens again, what should you do?  Go ahead and go back to bed, but make sure your phone, or NOAA weather radio is close by in case the watch is upgraded to a warning.

As for advisories, special weather statements, or public information statements, those are for less significant weather events.

By the way, Friday will be the 318 year anniversary the last great Cascadia “Mega-Thrust” earthquake.  It happened on the evening of January 26th, 1700.  Estimated to be at least a 9.0 somewhere off the coastline along the Cascadia Subduction Zone.

Earthquake Great Subduction Zone 1700 Event

It’s interesting that geologists didn’t know much about it until around 20 years ago.  They put together the pieces of the “puzzle” (#1-3 above).  Most interesting to me is the drowned trees in some bays.  The tree rings pegged the last growing season as 1699.  Good stuff.  You can read more about it here:

https://blogs.scientificamerican.com/rosetta-stones/thunderbird-and-the-orphan-tsunami-cascadia-1700/

and the Wikipedia article which seems pretty reasonable:

https://en.wikipedia.org/wiki/1700_Cascadia_earthquake

 

Chief Meteorologist Mark Nelsen