I know there's a super-mega weather thread, but this is basically an amber alert for horticulturalists.
http://www.weatheroffice.gc.ca/warni...274cweg-072400
City of Calgary
3:15 PM MDT Sunday 29 May 2011
Frost warning for
City of Calgary issued
Patchy frost developing overnight tonight.
A dry airmass and clearing skies will produce patchy frost overnight tonight across much of Southern and Central Alberta.