For those who think that a spring like a sheep is coming soon, think again.
Very heavy rain and flooding will come on Monday, the result of a strong atmospheric river. Some lowland locations will get 2-4 inches on Monday, with double that in “favored” mountainous locations.
The source of our wet future is a river with a strong atmosphere, a narrow region of great moisture, originating in the subtropics. To illustrate, here’s a graph of total surface-to-atmospheric humidity at 4 a.m. Monday. As you might have guessed, red is the largest number.
This atmospheric river begins north of Hawaii and heads northeast right into our region.
But not only the humidity but also the rate at which the humidity approaches our area.
That’s why meteorologists love to see Integrated steam flux (IVT), an impressive-sounding term that actually means wind speed multiplied by water vapor. Just drop the term “IVT” in your conversation and your friends and family will be impressed!
Here’s the plot of IVT at 4 a.m. Monday. The blue values are very high. A fast-flowing moist river is heading straight for us.
And when that moist river is forced up by the terrain of our region, an incredible amount of rain is released. Consider the University of Washington’s latest high-resolution precipitation forecast for cumulative totals through 4 a.m. Tuesday.
OH. 2-3 inches above Puget Sound and 7-10 inches in the mountains. Heavy rain shadow from Sequim to northern Whidbey Island.
The high-definition, but lower-resolution, European Central model will also be for a big event, with 3-4 inches south of Puget Sound, and even Portland getting a serving. of wet action. The Olympics and the coastal mountains receive incredible rainfall.
For snow lovers, this won’t be the event you’d expect, because atmospheric rivers are often associated with warm air and this is no different. On Monday, snow levels will rise to 5000-6500 ft, so heavy rain will fall on the passes.
I won’t go skiing on Monday.
With such heavy rainfall, local rivers will rise rapidly and flooding is expected. This is the latest river forecast from the NOAA/NWS River Forecast Center in Portland. Mild to major flooding on some (orange and red dots), which is dramatic as rivers are starting to dip below normal after recent dry weather.
The Snoqualmie River will be very, very close to major flooding (see river level chart below). Expect some roads to be closed.
