Google Now Issus

Why has my Google Now weather card disappeared on both my Nexus 7 android tablets and my Galaxy S2. I've checked the settings for weather - all on and I've asked for weather reports and it brings it up, but when you open Google Now later no weather card appears? Has anyone else had this happen?  I don't presume to understand the witchcraft by which Google Now collects my information and presents the future to me. But seriously, sometimes some cards show up that I think should always be there. Sometimes they don't. You could always "Clear Cache/Data," "Force Stop" and re-open the app. See if a fresh "reboot" of GNow helps.