Thursday, January 21, 2016

Tons Of Rain!

Thursday, January 21, 2016
5:45 p.m.

It's been pretty darn wet today. I could explain it with satellite imagery, models, maps, and all that jazz (and I will), but all you really needed to do was to go outside and look at the size of the puddles, both on the road and off it. There was an astonishing amount of puddles today.

Credit: National Weather Service

Let's take a look at some 24-hour rainfall totals around the region. At least two inches everywhere on the Coast, with especially heavy rain north of Willapa Bay and south of the mouth of the Quinalt River. As is usual, the southwestern slopes of the Olympics took home the bacon, with many spots reaching 5 inches. Even the Puget Sound region has gotten a substantial amount of rain, with areas on the northern Kitsap Peninsula getting the most, followed by the area between Seattle and Everett. The rainfall patterns here are very influenced by topography; note the dramatic rainshadow to the northeast of the Olympics, and note how much the precipitation increases as soon as air flowing off the Pacific comes aboard the Washington Coast.

Snow levels are high, and there is an avalanche warning for the Cascades. Stevens Pass was closed for some of today due to avalanche danger, and Snoqualmie was closed pretty much the entire day (and remains closed). Much of the precipitation falling in the mountains has been in the form of rain, and this greatly increases avalanche danger because it weighs down any snow "layers" that have recently accumulated and makes them much more unstable. I was caught in a minor avalanche inbounds at Alpental once on a run aptly named Adrenalin, and it was very scary. Don't go in the backcountry right now.

There is one atmospheric phenomena that routinely brings mild temperatures, high snow levels, heavy rain, and a distribution of rain heavily influenced by topography to our region. And the name of this infamous phenomena is the atmospheric river. Or, more colloquially, the Pineapple Express.

08:30 pm PST, Tue 19 Jan 2016
Credit: UW Atmospheric Sciences Water Vapor Imagery

Our current system (below) actually began life as an extremely sexy storm way out in the Pacific. It's not too often that we see storms take on such a picture-perfect appearance. You can clearly see the warm front, cold front, and occluded front, and if I could go back a little further in the satellite loop, I bet I would be able to see a pronounced dry slot near the center of circulation as well. I apologize for the tangent; I just had to show that satellite picture!

Anyway, that storm has weakened significantly over the past 48 hours but is still dumping heavy rain over our area. Do you notice how it is transporting a steady, slow-moving stream of moisture from the subtropics into our neck of the woods? That's why we call them atmospheric rivers: they don't move much side to side, preferring instead to transfer moisture and rainfall continuously into one place. 

06:00 pm PST, Thu 21 Jan 2016
Credit: UW Atmospheric Sciences Water Vapor Imagery

You can see the atmospheric river even better with this morning's model simulation!

Valid 04:00 pm PST, Thu 21 Jan 2016 - 12hr Fcst
Credit: UW Atmospheric Sciences WRF-GFS Model

This rain will continue throughout much of tonight before finally ending early tomorrow morning and transitioning to showers. The warm weather and avalanche danger will continue, but it should subside somewhat. We'll have showers over the weekend, drier weather early next week, and then the possibility of another wet and warm atmospheric river on Thursday. I'll keep you posted!


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