What's "freezing at the surface" mean?

Here's what I'm referring to:
Tonight: Mostly cloudy. Freezing level 3500 feet. West wind in the passes around 10 mph.

Thursday: Mostly sunny. Afternoon pass temperatures in the 30s light wind in the passes..

Thursday night: Mostly clear. Freezing level at the surface. East wind in the passes around 10 mph.

Friday: Mostly sunny. Freezing level at the surface. Afternoon pass temperatures near 30 wind in the passes light..


Friday night: Mostly clear. Freezing level at the surface..

I don't understand. Is that common verbage? Surface of what?
Thanks.

[Surface = sea level, as far as I know.]

Or, perhaps, I am totally wrong. Thanks for setting it straight!

Freezing level at the surface usually means at the pass/road level. Sometimes the freezing level will be at 3500-4000 ft except lower at the "surface" of I-90 (for example, 3000 ft) because of the unique characteristics of a pass. Perhaps it's the wind chill funneled down to the pass level.

I believe that often there are surface winds that carry cold air from east of the crest through the passes. In this situation, air temperatures at the passes can be below freezing even though the 'free air freezing level' is significantly higher away from the passes; the NWAC weather forecast will then contain language like 'freezing level 5000 ft, except near surface cascade passes'. I agree with Volcanogrrl that the usage she quotes is a little different than has been used in the past.

In any event, I would like to take this opportunity to say once again what a wonderful and helpful resource the NWAC avi/wether forecast/telemetry is! How did people know where to go skiing before the internet?

Actually, if it just says "freezing level at the surface" I think that generally means freezing at sea level.
Looks like hard snow conditions this weekend...

It sounds to me like she's quoting from the wsdot passes report. In that case, sea level would have no relevance. When freezing level is at "sea level" they say so.

wsdot.wa.gov/traffic/forecast/Default.aspx?zone=WA519