The Upcoming Deluge

We are about to enter a very wet period, with the potential for bankfull rivers and even some localized flooding.

Let me start by showing you the total precipitation accumulation forecast over the next ten days over the region (from the European Center model, below).

Wow.   Over ten inches in some locations in the Olympics and coastal mountains and 5-10 inches in the Cacades.  Even significant precipitation east of the Cascade crest.

The UW model for the same period provides similar large totals, with over ten inches in the Cascades and Olympics and 3-5 inches over the lowlands of Puget Sound.

Temperatures will be cold enough to bring large snow totals.  Below
is the prediction accumulated snowfall over WA State for the same period.  Over FOUR FEET over the North Cascades and snow over lower elevations across the northern Columbia Basin.

The first major hit of rain and snow (in the mountains) will occur tomorrow (Saturday) and the a stronger event on Sunday night and Monday morning.

Let's take a closer look over the next few days.

Trough 4 AM Sunday, the regional gets a nice wetting, but nothing excessive.

But with heavy rain on Sunday night, by Monday morning, the story is very different.....very heavy precipitation totals in the mountains.     A profound rain shadow northeast of the Olympics.

One day later (Tuesday at 4 AM), amazing totals over the mountains and even quite heavy south of Seattle.  Continued rain shadowing from Sequim to Whidbey Is.

Rivers will respond.   For example, the Northwest River Forecast Center is predicting that the Snoqualmie River will rise to "action levels".  

This is climatologically the wettest time of the year, so it is nice to see that the atmosphere is following the calendar. 😁