Left wind to find wind. At noon, there was a southwest wind at DC, but it was extremely gusty and shifty, the way it tends to be when the wind is out of the north along the Wasatch Front. Arriving at Jordanelle about 12:45, I was greeted by wall-to-wall whitecaps generated by a strong north wind. Wasn't sure my 4.5 (the smallest sail I had with me) would be small enough; it was, just. The wind was a bit up and down, but I was able to plane most of the time and got some screaming reaches. Almost no one else around; I saw a total of two mototboats in two hours. When I quit at 3:45 the wind was about 20 MPH with gusts into the low 30s.
Meanwhile, back at DC: http://homepage.mac.com/jsouthwick/PhotoAlbum43.html
Conclusion: Jordanelle appears to be a very valid option on north wind days.