OK, it’s not ideal, but I have found a paper with some kind of average or “climatology” for freeze levels in the Northern Hemisphere. It’s at this link:
http://geotest.tamu.edu/userfiles/213/i1520-0442-013-23-4137.pdf
and has a map in meters. There are also seasonal maps and a standard deviation map.
The live version of the present freeze level map is as this link:
http://www.eldoradocountyweather.com/current/freezinglevel.html
This map is the present state (measured in feet. I’ve not found a map in meters yet, so we get to ‘adjust’… ) and I’ve not found a map for “this month” or other averages. The ‘freeze level’ products seem to be mostly aimed at aviation and they care about “now” and “soon”, not averages of “back then”. A conversion chart for your convenience:
1000 meters is 3281 feet
2000 meters is 6562 feet
3000 meters is 9842 feet
4000 meters is 13123 feet
5000 meters is 16404 feet
As I read the pdf “paper” the monthly mean for January for North America (Figure 5) has a 2000 m line at about the border of Canada, a 3000 m line middle of the USA to about Georgia to San Francisco and the 4000 m line is down in Baja California to Orlando Florida.
I make that 6500 feet, 9800 feet, and 13,000 feet rounding down. So, when we look at this Freeze Level Map, is 6500 feet on the Canadian Border? Is 10,000 near Georgia? 13,000 feet in Orlando?
Freeze Level in the USA 7 January 2011
Uh, I’d make that a ‘No’…
And I’m afraid to ask what that Beige Blob is over the Great Lakes and New England… It seems to be ‘below the graph range’?…
It was a little better on 5 January 2011 when we first saw one of these graphs, but not by much:
Musings from the Chiefio 
“And I’m afraid to ask what that Beige Blob is over the Great Lakes and New England… It seems to be ‘below the graph range’?…”
I’d say it’s below freezing even at sea level, since black is freezing level from 0 ft to 500 ft.
I think that map program has problems determining the temperature when there is rain and freezing rain present. When this happens you get layers of freezing and above freezing temperatures. On today’s map there is an area of gray in the US NE and also an area with the wrong freezing level in northern Manitoba. Both have freezing rain, fog and mist. Black areas appear to be freezing level at the surface, which can be verified on a surface map.
The 850-hPa (approx 5000 feet) and 750-hPa (approx 10000 feet) have the freezing levels on them (heavy dashed lines). They are constant pressure charts:
http://www.aviationweather.ws/012_Atmospheric_Pressure.php
There are many of these charts available. Here is an example of an 850 hPa:
and 700 hPa:
Both maps have zero line quite far south at present. Of course these maps change every twelve hours.
This may be a clearer map. It is from the GFS model with data provided by NCEP and plotted using GRADS:
http://img233.imageshack.us/img233/200/frrezlev.png