So far this summer there has been no rain in the valley  But usually a few inches of rain fall there each summer
Since only one week of summer is left, it will probably rain in the valley within the next week
On average, there are a few errors in an issue of the journal Periodos. Aisha has finished proofreading all but the last two pages of an issue of this journal but has encountered no errors. So there are probably errors in the pages she has not yet checked in this issue of the journal.