The Sunday Snow Forecast for Western Washington

The Seattle Times has a headline about possible snow in the lowlands on Sunday, and I have gotten a number of emails about it.....so let's examine Sunday's situation.   The bottom line: there is little to worry about.

This morning dawned clear and cold, in fact, one of the coldest mornings so far this fall.  Temperatures ranged from mid to upper 30sF near the Sound to low 20s away from the water.  But travel east of the Cascade crest, and lots of locations dropped into the lower teens, even single digits in low/cold spots.  This cold  is allowing Mission Ridge and Crystal Mountain to make snow and open.

Some frost around the region, but little fog.  Why?  The air is simply too dry.

There will be no precipitation today and Saturday.  But Sunday, a low pressure system will be approaching from the southwest, spreading clouds and precipitation into the region.

To illustrate,  here is the predicted surface chart for 1 PM Sunday, including sea level pressure (solid, lines), surface winds, and low-level temperatures (color shading).  You can clearly see the low pressure center offshore and it you look closely, you can see southerly winds and warmer air pushing northward to its east.  In fact, there is a weak warm front pushing northward along the WA coast.  Easterly winds are over western WA and temperatures are cool, not cold (green colors).



Moving to a level around 5000 ft (850 hPa),  southerly winds and warmer temperatures (yellow/orange colors) over western WA are apparent.  Not good for snow.

The latest  UW WRF high-resolution snow total prediction through 10 PM Sunday, shows no snow near Puget Sound and some light snow at higher elevations.  Just too warm.

Now, if it possible a few flakes could be observed when the precipitation starts in the Seattle area on Sunday morning, thanks to intense cooling from evaporation as the flakes fall into dry air below, but this will quickly turn to all rain.  There could be a dusting just to the southeast of the Olympics and over the higher terrain of southwest WA.  If you are driving on  I5 over SW WA during the initial light snow period, slow down and making sure you have adequate following distance...we don't need another Spokane accident scene.

If you want more information, do what I do and go to Seattle SnowWatch, a website that has the best collection of snow/temperature data for the region that exists.  This is a joint UW/City of Seattle project.

Finally, notice how dry this November has been.  As described in my next blog, this has been the driest November since 1976!