Drops in the bucket for Valentine’s Day, then a rush of rain

Weather Blog

PORTLAND, Ore. (KOIN) — Raindrops in the bucket for Valentine’s Day and a fire hose of moisture expected for this Presidents’ Day weekend. I know, you could have used a dry weekend to ring out the lawn or, as many residents are dealing with across the state, flood damage. 

If you have travel plans for President’s Day weekend don’t be caught off guard by the snow you’ll be plowing through over our mountain passes. What does all this wet weather mean for rivers that recently dropped below flood stage? 

Rain chance increases Friday night.

First, we must find the answers to these key questions:

  1. What’s the forecast temperature? 
  2. Where will the heaviest rain fall? 
  3. How much rain will fall in a 12 or 24-hour period? 

Let’s get into #1. Warmer temps in the winter are bad news bears and usually lead to snowmelt which only makes matters worse as we saw with flooding last week across the Pacific Northwest. This time, colder air will be arriving from the Gulf of Alaska in unison with an extended plume of moisture called an atmospheric river.  Not all atmospheric rivers are married to warm tropical air, which is why we don’t always refer to these rivers aloft as a “Pineapple Express”.  Temperatures in the Willamette Valley will stay in the mid 40’s this weekend. Overnight lows above freezing. Freezing levels will drop below mountain passes this weekend. That’s good news. Last week we had freezing levels all the way up to 7,000’. 

This is the atmospheric river that will make Saturday water-logged, and bring back our much needed snowpack.

Number #2 can be determined by closely watching models and understanding how topography interacts with the air aloft. Under a mostly westerly flow at the surface, the heaviest rain is expected to hit those locations where the terrain rises: coast range, west slopes of the Cascades. 

And #3, how much rain will fall? On the coast and coast range near Tillamook, possibly up to 1.5″ to 2” of rain Saturday. The wet weather backs off a little Sunday, adding another ½” or less of rain to our presently saturated ground. The valley may see 1” of rain for the weekend total. 

The biggest impact this weekend will come to you courtesy of snow. Anywhere from one to almost two feet of snow could fall across the Cascades, and this will no doubt impact your drive over mountain passes. Stay close to us for forecast updates as there is a good chance we could see winter storm watches issued by your local NWS office. 

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