There is a beautiful WF Shield (WFS) over the Atlantic Ocean, south of Iceland. No radiosondes, therefore. There is another one over Eastern Europe that looks more lumpy in the IR.
The diagram to the left is a sketch of the identifying characteristics of a WFS which I have learned from SATREP. The parameter is called temperature advection (TA700) and I usually find a WFS by locating these contours, red is for warm advection and blue (dashed in the SATREP report) is called cold advection. I'll try to describe these in another post. Other characteristics are being associated with a trough and ridge in the H300 (geopotential height contours at 300hPa). The isotach contours form a T, where the top of the T is in line with the WA line of clouds and the vertical part of T is in line with the CA area.