Park and Helliwell [1971> suggested that whistler ducts might be caused by plasma interchange of geomagnetic flux tubes driven by thundercloud electrostatic fields. At present, this is the most favored whistler duct creation mechanism. Theoretical formulations have been developed to calculate high-altitude electric fields due to electrified clouds, taking into account the presence of the ionosphere. Previous studies have calculated the values of these fields, making use of approximated conductivity profiles. Calculations are undertaken using more accurate representations of more modern conductivity profiles than those used previously. Preference is given to experimental rather than theoretically derived conductivity profiles. These calculations indicate that under typical conductivity conditions the high-altitude electric fields from even giant thunderclouds are too small to create a realistic whistler duct in a realistic period. This is the case for both day and night conditions. ¿ 1998 American Geophysical Union