*Gur can estimate that based on the mount's speeds, they are not fast enough to make it around the edge of a typical storm before the storm catches up with them unless they were right at the lateral edge of the front. Fleeing directly away from the storm might work for a while (the mounts can hustle about 50 miles per hour), but it would waste a lot of time, and if the mounts fade, they'll have to walk a significant amount of desert by foot, with each hour lost on the steeds being about two weeks on foot.*