Short answer: Not possible (yet).
We released the base version of our Alerts / Triggers feature. We plan to beef it up drastically in the coming months.
This is great feedback, and by all means a valid use case. Is the following an example of what you mean?
" If temp. goes above 80 degrees F, send me notification. Keep sending notification every hour until temp. goes below 72 degrees F (and send me notification when this happens too) "