Snow will fall on Central/Northern Puget Sound but won’t last

The most powerful high-resolution meteorological tools are available for tomorrow night’s snow event. Parts of the lowlands will snow–up to several inches thick in places.

But it won’t last.

And tomorrow’s situation is not favorable for lowland snow accumulation in our area.

The Golden Rule of Snow

Snowfall is NOT the depth of snow.

This will be very important for the upcoming event. And this subtlety is often missing from the analyzes of some amateur weather sites.

An important issue is the temperature of the ground and especially the road surface. Here are this morning’s values ​​from the city of Seattle’s Snowwatch website, with the temperatures in the boxes showing road surface temperatures. Most are in their 30s to almost 40F.

The air above us now has a freezing level approximately 1300 ft (see below from SnowWatch below for SeaTac Airport). Snow melts below that, takes about 1000 ft to reach snow level, underneath it all is rain. So the current snow level is about 300 ft.

With extended showers this morning, some hills are higher in the area with snowfall (see below). And Cascade passes have been hit hard, with the lines being a must-have in Stevens Pass right now.

About 1000 ft ASL in Bellevue. Image courtesy of Dr Peter Benda

Snow event tomorrow

As noted in my previous blog, a front will approach our area tomorrow afternoon and evening, bringing rain. Cool air will be in place….just at the edge because it’s cool enough to allow the snow to reach sea level.

But something else will come into play. Cool by melting and evaporating.

As precipitation falls into the drier air below, it can cool by evaporation, helping to push snow levels to the surface. Snow falling into the air above freezing also melts…and that takes energy. The result is even more cooling, with the degree of cooling dependent on the intensity of the rain.

On the other side, warm sea air will move in behind the front!

Now that you’ve got your training done…. let me show you some graphics that I rarely show on this blog: a precipitation forecast map that shows whether the amount of precipitation that reaches the surface is rain ( black and gray) or snow (color).

And to make it even better, these forecasts are from the highest resolution UW system (1.3 km grid distance).

First, here’s the forecast for total rainfall for the three hours ending at 4 p.m. Tuesday. Snow fell around the Olympic Peninsula, but heavy rain offshore and light rain inland.

During the 3 hours ending Tuesday at 10 p.m., rain (and strong southerly winds hit the coast), while snow intensified on the Olympics and the Kitsap Peninsula, where a southeasterly countercurrent increased the amount of rain. rain. Some light snow falls from downtown Seattle to the north.

The next three hours (ending at 1 a.m.) are the heart of the ski game north of Puget Sound (see below). The higher elevations from Lynnwood to Everett can get several inches of snow (NOT SWITCH DEVICE).

But note the rain (black and gray) moving quickly from the south.

Sadly, the same image that ended at 7am shows rain sweeping through the lowlands, but the snow continues at higher elevations.

24 hours snow total ended at 4 a.m. Wednesday with snow north of Seattle and Kitsap.

Snow depth (in meters…sorry) at 4 a.m. Wednesday was much less impressive, with only a limited number of lowlands reaching 0.1 meters (3.7 inches) )….and that amount of snow will melt quickly at that point.

I told the class that I was pretty sure Wednesday wouldn’t be a snow day at UW. A very good event for skiers though….