Getting Ready for a Deluge

Just last Wednesday I was writing a blog about the weather we had seen during the first half of November.  In that blog I talked about how dry we were during the first 15 days of the month.  We had only recorded 0.91 inches of rain at Sea-Tac.  That is a mere 14% of the rain we typically see over the entire month of November.  I mentioned at the end of that blog that we would be catching up on rain over the coming days.  I’m here to tell you that we will be playing major league catch-up on Tuesday. 

What if I told you that some cities around Puget Sound are likely to pick up close to an entire month’s worth of rain in a matter of 48 hours?  This is a very real possibility starting tomorrow. We’re not talking about just any month here either… we are talking about November, our wettest month all year where we average 6.57 inches of rainfall at Sea-Tac Airport. 

On the first graphic, you can see the forecast rain amounts between now and Wednesday morning. This is a computer forecast model, so these amounts are not exact.  What this graphic does do is paint a great picture of just how much rain we’re expecting.  2 to 5 inches are likely around Puget Sound over the next 2 days.  That is an incredible amount of rain.  I just checked the almanac and the rainfall record for Tuesday is 1.14 inches of rain at Sea-Tac… we will shatter that record tomorrow. 

Why so much rain?  If you look at the satellite image from late this morning, you can see a plume of moisture offshore extending well out into the Pacific Ocean.  That is known as an “atmospheric river,” and it will be pointed at Western Washington tomorrow.  Think of it as a fire hose that will be turned on all day long.    

Flooding Potential

As you can imagine, all that rain is going to be running off into our local rivers, causing them to swell over the coming days.  The one thing we have going in our favor is that the rivers are running low right now.  They have not had a real test when it comes to heavy rainfall this season so they will be able to handle a lot of this water. 

That being said, this is going to be an incredible rainfall event, and some rivers are expected to reach flood stage.  The most likely rivers at this point are the Skokomish, Elwha, Newaukum, Puyallup, and Stillaguamish Rivers.  A Flood Watch is in effect for the rivers flowing off the Olympic Mountains.  4 to 7 inches of rain is forecast over the Olympics with this storm. The Cascade Mountains are likely to pick up 3 to 8 inches of rain.  These rivers look to crest late Tuesday into Wednesday.  It’s not out of the questions that a few rivers may still be above flood stage on Thanksgiving. 

Damaging Winds Expected

We have covered the rainy side of this storm; now let’s touch on the windy side.  Winds have been breezy this morning, but this is only a taste of what’s to come.  Winds will be peaking later tonight through early Wednesday morning.  The strongest wind will be focused north of Everett and along the coast.  A High Wind Warning goes into effect at 7 p.m. for the Washington coast, Whatcom, Skagit, Island, and San Juan counties at 7 p.m. this evening.  Sustained winds 30 to 40 mph with gusts up to 60 mph are expected.  The rest of the sound will be under a Wind Advisory with winds 15 to 30 mph and gusts up to 45 mph. Winds will start easing by tomorrow afternoon. 

We’ll keep you up to date with the latest on this storm here at www.kirotv.com.  You can also follow the heavy rain moving into your neighborhood with our interactive radar.  Also, if you haven’t done it yet, now is a very good time to sweep up the leaves and clear the storm drains.  You don’t want to be the neighbor who turns the cul-de-sac into a swimming pool.    

-Sam Argier, KIRO 7 Morning Meteorologist