WeatherWatcher: Winter Solstice Storm

 

Washed out driveway in Innis Arden.
Photo courtesy City of Shoreline

The first day of winter sure brought us a day with almost all the kinds of weather we'd normally expect in winter. 

Winds in the morning gusting to 35mph, heavy rains, then accumulating snow. 

Seattle broke records, for warmest December 21st, most rainfall on December 21st, and all in the same day as recording measurable snowfall. This has happened a number of other times on other days in Sea-Tac's record history but by about 1-2 degrees cooler in difference. 

Flooded garden in Richmond Beach

The most recent weather pattern that matches this storm was on November 19-20, 2003. On the 2003 storm we had winds gusting to 35-45mph by 11pm, heavy rain overnight and it turned over to snow shortly after 5am. The snow was a quick 1-3 inches before melting off as well.

Back to 2020, in Shoreline we had a brief warmup to 54°F, with breezy southerly winds up to 30mph. 

When the cold front hit shortly before 1pm, winds abruptly switched to the northwest and we started seeing gusts up to 35mph. That's when the heavy rain started, and the temperature dropped down to 42°F within 30 minutes. 

The temperature continued a slow decline after that from 42°F all the way down to 33°F at 4:45pm.

Daily high and low temperatures in Shoreline, compared to eight year average in December 2020

Most rain gauges in the city, including my Richmond Beach station, recorded just over 2 inches of rain for the day. Some spots saw up to 2.4 inches of rain, other spots as little as 1.5 inches of rain. There were a lot of microbursts of rain embedded in this cold front that made for highly localized downpours.

Total rainfall and snowfall in Shoreline for December 2020

Snow begin mixing in with the rain at about 4:40pm or so before making the rapid transition to all snow at most spots above 100 feet in elevation. 

If you were close to Lake Washington or the Puget Sound it was too warm for any measurable accumulation in most spots. Everywhere a half mile or more from the water saw some accumulation. 

Places like North City and Aurora Avenue saw about 1" of wet slushy snow on the ground. It even accumulated on some of the side streets and in parts of the main roads for a short time.

1 inch of slushy snow accumulated on side streets.
This is looking across 15th Ave NE east towards NE 179th St
Photo by Brittany Ledyard

By around 7:30pm most of the snow had changed back over to rain as precipitation lightened up. Once the storm front passed through there were a couple of weak convergence zones but none got near Shoreline. 

We are now heading into a short dry period before we get more rain showers returning Christmas evening. 

Temperatures overnight into Wednesday morning and Thursday morning will reach freezing or dip below freezing, leaving ice and frost in places, including roadways.

There are now early indications that we may see more winter weather next week, something we need to keep a close eye on when we get towards the weekend.

For current weather conditions visit www.shorelineweather.com