An attempt is made to approximate Dst variations during geomagnetic storms in terms of lognormal distributions. Dst variations for the entire duration of a geomagnetic storm are found to be fitted by a lognormal distribution reasonably well, indicating that by using Dst variations during the main phase, how Dst recovers during the recovery phase can be predicted. This is very useful for space weather predictions. On the other hand, there are quite a few geomagnetic storms that cannot satisfactorily be fitted by lognormal forms because of a long duration of the recovery phase. During the recovery phase of these abnormal storms, highly fluctuated interplanetary magnetic fields are seen, such that these events must represent HILDCAAs.