What's "freezing at the surface" mean?

This forecast you posted above is for the pass, not Seattle.. If you look at the Seattle forecast it has no mention of freezing or snow.   I don't think a Pass forecast would make any references to sea level, it wouldn't make sense IMO.   Just a hunch on my part.....

I meant to post the forecast for the pass where the term was used and I was giving the Seattle forecast as a reference so I didn't have to post all of both forecasts.  Sorry if that was not clear.  Since it doesn't seem like there is any consensus I have put in a question to the NWS.  Hopefully, they will respond and enlighten us all.

I meant to post the forecast for the pass where the term was used and I was giving the Seattle forecast as a reference so I didn't have to post all of both forecasts. Sorry if that was not clear. Since it doesn't seem like there is any consensus I have put in a question to the NWS. Hopefully, they will respond and enlighten us all.

Cool. I was hoping we had a weatherman here that would shed some 'official light' on the subject, and maybe that will still occur. Funny how such a simple term I have always taken for granted is interpreted many different ways.

I think freezing level at the surface can be used a couple of different ways.

1. It can mean that it is freezing everywhere at the surface. i.e. in Eastern Washington at 1-2000' and in Western Washington essentially at sea level.

2. Used in the mountains it can mean that a cool easterly flow is coming over the passes and Cascade crest such that while you are in that flow it is freezing. but that may also imply that it may be warmer aloft and along the west slopes of the Cascades (or other mountain range). The wording would usually be something like this in the latter case, either: "Freezing level (or snow level) 4000' west slopes of the North Cascades and at the surface through the passes and near and east of the crest."

The freezing level is the elevation where freezing takes place. If the freezing level is “at the surface” then the temperature is at or below freezing at ground level. It is actually vague and misleading terminology for backcountry users.

The Washington Cascades act to dam up the cold pool of air in eastern Washington. This “dam” is about 5000 ft high. As Gary pointed out, this is why it is often cold at the surface in the passes and warmer as you go higher.

By focusing only on phrase “freezing level at the surface in the passes” you are likely to be misled. You need to focus on the entire statement, which often says something like “ the freezing level is at 6000 ft, except at the surface in the passes”. This statement means that the temperatures are below freezing in the passes, but as you climb higher, you are likely to climb into air that is above freezing until you climb above 6000 ft. In the Washington Cascades with easterly winds blowing through the passes in the winter, temperatures generally remain below freezing below 5000 ft east of the crest. If the air west of the crest is above freezing at elevations at or above 5000 ft, then (if you are at or east of the passes) you are likely to climb into that warm air at elevations above 5000 ft. If you are west of the crest, you will remain in warm air until you climb above the “freezing level”

Actually, that 6000-ft freezing level is a critical factor in determining if there will be freezing rain or snow in the passes. If the freezing level is at the surface in the passes but above 6000 ft elsewhere, and precipitation is forecast, then there will be freezing rain in the passes. If it is below 6000 ft under the same circumstances, then it will snow in the passes.

Hope this helps.

Bryan Scott-retired weatherman.

Bryan ,
Thanks for the fine tuning tip of 6000'vs. 5000' freezing level.

I've often wondered about the term too, so I sent an e-mail to the NOAA forecasters when I first read the thread.  Here's the reply:

> Hi -  do you mind if I post a snipped portion of your reply?

" ... That would be fine.

   <<names/e-mail address snipped>>

Tony,

The snow and freezing levels in our forecast are in respect to sea level.  "...at the surface" is a reference to a snow or freezing level at or below sea level.

Thanks for your question.  I hope this helps.  Thanks for using our website.

and this...

I read the linked string *after* first replying to you.  The term is indeed rather vague and ambiguous.  Therefore, I e-mailed the entire forecast staff to see what their interpretation is.  I'll get back to you in about a week once everyone's had a chance to reply.  At the very least, "freezing level at the surface" tells me that the temperature above the surface is going to be sub-freezing.