Drought-Buster Wet, Cool Weather Ahead

 As many suspected, with the rapid collapse of El Nino and the progression into spring, the weather patterns have shifted, opening the door to far wetter weather over the Northwest.

During the next 10 days, expect lots of precipitation, cool to seasonal temperatures, and even a good dump of snow in the mountains.

The official NOAA 6-10 day forecasts say it all (see below), with wetter than normal conditions and colder than normal temperatures over our region.

A vigorous weather system is arriving tomorrow, bringing a wet day.   The total precipitation through Friday morning at 5 AM is shown below.  A nice wetting for the entire region with some western slopes getting 2-3 inches.  That is a lot for late April.

But this is just the beginning, with multiple wet systems arriving over the next week.   The total accumulation through next Saturday morning (4 May) is impressive, with large areas of more than 3 inches.     Keep in mind you need to multiply that by roughly ten to get snowfall in the mountains.

Over the higher elevations, the temperatures will be cold enough for snow, with substantial accumulations through May 4th.  Some mountain locations will get several feet of new snow.

I suspect the snowpack will increase to around 80% of normal over Washington State and more than 100% of normal over much of Oregon within roughly 10 days.  

The latest NOAA River Forecast Center forecasts for 10 days out are for near-normal river levels.   For example, consider the Snoqualmie River (below).  Below normal now, but near normal in a few days...and staying that way.

This and subsequent wet periods are well-timed to ensure sufficient water levels this summer.

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Announcement:  I will do a special online zoom session at 10 AM on Saturday for Patreon supporters, with a deep dive into the upcoming wet period and the implications for this summer.  Plus, I will answer your questons.

The Other Type of Mountain Wave Cloud

 Folks love to talk about lenticular clouds, which are generally produced by air moving up (and down) downstream of a mountain barrier (see picture below).  Such clouds are generally found in the lower atmosphere at or just above the crest level of the mountain barrier that produces them.

Picture by Joel David-Aldridge

As shown by the schematic below, lenticular clouds, also called trapped lee wave clouds, often come in multiples downstream of the mountain barrier and have a lens shape (see below).    Such mountain-wave clouds are called "trapped" because the clouds and the motions associated with them are trapped in the lower atmosphere. Some folks think they look like flying saucers and more than one UFO scare has been initiated by such clouds. 

Why does the air go up and down downstream of the mountains?   Think of a kid's swing set.  You give the swing a push and it goes back and forth for a while.  Air pushed upwards by the mountain crest does something similar.

Interestingly, there is another type of mountain-wave cloud that is found much higher in the atmosphere, but still downstream of a mountain barrier.   In this case, the mountain wave energy propagates vertically in one very high amplitude wave, with high-level clouds just downstream of the mountain (see schematic below).  Such clouds can be associated with substantial turbulence aloft.

Certain conditions favor high-amplitude mountain waves, such as strong winds approaching the mountain crest and supportive changes in wind and temperature with height.

Yesterday was a super day to view a vertically propagating mountain wave just downstream of the Cascades.

 The image at 8:41 AM shows the feature clearly (below, see red arrow)

As did the image at 11:01 AM (below).

To show you how good the weather models have become, here is the simulated cloud field at 8 AM yesterday--the correct type of mountain wave cloud was evident.

Living here in the mountainous Pacific Northwest, we get to see mountain-wave clouds nearly every day, so it is important to know the two types.   And now you do.