Weather Blog

UW site provides valuable tools for chasing Seattle snow

UW site provides valuable tools for chasing Seattle snow
Snow falls at the Space Needle on Dec. 18, 2012. (Photo: Jonathan Cooper, Seattle Image Photography)

Snow forecasting is far and away the most difficult task Seattle-area meteorologists have, what with varying elevations, a warm body of inland water, two large mountain ranges, an ocean and stuff like convergence zones and rain shadows all wreaking havoc on trying to get that ultimate mix of cold plus moisture.

But now a relatively new web site aims to at least help figure out where snow has a higher chance of falling, with several new tools that track current temperatures, trends, estimated snowfall and forecasted temperatures.

The project, called SnowWatch was built from a partnership with Seattle Public Utilities and the University of Washington Atmospheric Sciences Department -- particularly Prof. Cliff Mass.

Here is a guide how to use the site:

Current Temps:

This is a mix of both ambient air temperature, measured at the standard 5 feet above ground level, and road temperatures (those listed inside a box) - to help know whether that snow that might be falling from the sky has any real chance of sticking to the roads anytime soon.



The temperatures are color-coded for increasing threats. An asterisk next to the number means snow is reported at that observation, but the site says only a few of those listed sites can actually report snow. You can go back as much as 5-6 hours to get the trend, or click on the "Temperature Trends" box to show the temperature change -- either over 1 hour or 3 hour periods.

Future Temps

If you want to see where we're heading, click on the "Forecast Temperatures" tab. This will show two forecast plots side-by-side -- one is the forecast from the National Weather Service forecasters, updated every 3 hours, and the other is the high-resolution UW forecast model temps, updated twice a day around 10 am/pm.



Estimated Snowfall

This very high-resolution map uses some of the data from their sister project RainWatch that measures current rainfall rates using an armada of weather observation and radar data and translates it into estimated snowfall amounts.



There are also tabs on there that show forecasted snow totals, both using National Weather Service forecasts and UW forecasts, like so:



Where's the snow level?

But perhaps one of the best tools might be the snow level estimation graphic, which uses data from sensors that collect temperature data in the lower atmosphere and mixes it together with weather data from planes coming and going into Sea-Tac Airport to give an hourly update on where the freezing level is.

The dotted line on the graphic shows at what altitude it's determined to be 32 degrees or lower -- in this case below, it's at 485 feet.



Now, a snow level is assumed to be as much as 1,000 feet lower than the freezing level because it can snow with temperatures a few degrees above freezing. So a freezing level of 1,200 feet would assume snow down as low as 200 feet.

But the freezing level is still important because obviously you won't have a freezing snow unless you're above the freezing level. In other words, a freezing level of 600 feet would have snow at sea level but likely not really a sticking snow -- or at least a very good sticking snow unless the rate of snowfall overwhelmed the melting procedure.

This map also does a good illustration of how the process of precipitation can help lower the snow levels. The freezing level was about 1,000 feet over Seattle early Thursday morning but dropped to 400-500 feet when precipitation began falling.

And finally, there are handy links to the National Weather Service Zone Forecast and any current Weather Warnings in effect.

If you like this for snow, I highly suggest also bookmarking their RainWatch site for when there is heavy rain, and WindWatch for information during wind storm.