Intense Cold Front Brings Heavy Snow and Substantial Precipitation to the Mountains

As predicted, a very strong Pacific cold front moved through the region yesterday, bringing substantial precipitation, including heavy snow in the Cascades.  Several mountain observing sites have received over a foot of new snow.

At Crystal Mountain Ski Area, the upper reaches were in white-out conditions this morning:

And the mid-elevations of Alpental in Snoqualmie Pass were a winter wonderland.

The National Weather Service has a Winter Storm Warning for the Cascades and a Frost Warning for the lower slopes:

The visible satellite imagery shows very cold, unstable air approaching the Washington coast (see below)

The white and dark areas offshore show strong cumulus/convective activity resulting from very cold air moving over warm water.  This creates a large temperature change in the vertical, which produces convection:  small-scale upward and downward motions in the atmosphere.

Upward motion produces clouds and rain, and downward motion creates a clear area.

The radar image last night showed the narrow rainband associated with the intense front (see red arrow). There was also a world-class rain shadow over the North Sound area (light blue arrow).

All of this was nearly perfectly predicted by our models.

Precipitation amounts with the front and trailing showers have been impressive, with the totals through 10AM shown below.

Wow...over three inches in some locations!

Importantly, a persistent Puget Sound Convergence Zone has resulted in heavy precipitation around Snoquamie Pass and the headwaters of the Yakima River (see below)

As a result, there will be plenty of water to fill the Yakima Reservoir system as well as to produce high flows in the entire Yakima river system (see forecast below)

Furthermore, the substantial snowfall will help maintain river flows later in the season.

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UPDATE!    Snoqualmie Pass has been closed due to heavy snow!

Announcement

I will hold a special online Zoom session at 10 AM on Saturday for Patreon supporters.  Will answer questions and talk more about the recent Sound tornado and about drought issues.

A Very Strong Cold Front Will Cross the Northwest on Tuesday

The Northwest is known for its weak cold fronts, since the relatively warm Pacific Ocean warms, near-surface, cold Arctic air before it arrives in our region.

But sometimes conditions allow us to get a relatively strong cold front, with a sharp temperature decline and profound wind shift...and this will happen tomorrow afternoon and evening.

A strong cold front that will bring substantial snow to the mountains and further ease any drought worries.

Let me show you the latest forecasts!

The predicted sea-level pressure (brown lines), near-surface temperatures (colors), and winds (arrows) at 5 PM Tuesday are shown below.   A strong front (indicated by the red dashed lines) has reached the Washington coast.

A profound wind shift (from southwesterly to northwesterly) is associated with the front, with cold air (blue) behind.  Mama Mia!  This is a spicy front.

The front is even stronger aloft, as shown by the predicted temperatures at 850 hPa (about 5000 ft) the next day (the front is crossing eastern Oregon at this time).  Dark blue is cold air. Cold enough for snow in all the mountains!

A simulated radar image for Tuesday evening shows an intense line of precipitation with the front (look for the thin yellow line that crosses the coast near Hoquim and extends to near Bellingham).  Pro-tip:  You will not want to be outside when this line is over you.

The line will be associated not only with heavy precipitation, but also with a dramatic wind shift and temperature decline.

To illustrate, here are the predicted temperatures at Hoquiam, on the Washington Coast, for the next few days.   Frontal passage drops the temperature from 49F to 39°F- a substantial decline on the coast.  On the western slopes of the Cascades, the temperature drop will be roughly TWICE that amount.

All this means snow in the mountains.   Below is the predicted snowfall through Thursday at 5 PM.  A foot or more in some locations!  A huge benefit this time of the year.

This surge of cold air originated over the Arctic and pushed southward into Alaska and then across the Gulf of Alaska.   Interestingly, the Gulf of Alaska is substantially cooler than normal (see below, blue indicates cooler than normal), which allows the chilly air to reach us with less ocean warming.

Finally, here in Seattle, the strong front will bring blustery winds tomorrow afternoon (see plot from Seattle windwatch below at 11 AM).  With the new leaves on the trees, there could be some scattered power outages near the coast and Puget Sound.  

Enjoy the weather show tomorrow!