Almannavarnir in Iceland did send out this warning earlier tonight. There is a heavy rain going over south of Iceland. This means that there is a risk of ash floods from south side of Eyjafjallajökull volcano. As that area is still covered in heavy ash after the last year eruption. People traveling in this area is advised to monitor the news or the website vegagerdin.is and vedur.is for more information. The area in the most risk of flooding is Þórsmörk and other rivers that come from Eyjafjallajökull volcano. The most heavy rain is forecast to start from 22:00 UTC and last until 12:00 UTC on 22 April 2011. But this forecast can change without any warning at all. So it is important to monitor the weather forecast for changes.
News about this in Icelandic. Use Google translate if you want to solve a puzzle.
Varað við vatnavöxtum undir Eyjafjallajökli (Icelandic, sunnlenska.is)
Varað við vatnavöxtum á Suðurlandi (Icelandic, Rúv)
Vara við úrkomu og vatnavöxtum (Icelandic, mbl.is)