weatherUSA provides a free, real-time weather alert service which sends out weather warnings, watches, and hurricane information as soon as they are issued by federal agencies (such as the National Weather Service). Alerts are sent to subscribers in the warned areas via text messages (SMS) and e-mail. Premium users can also receive alerts via voice (phone) call.
You can select warnings to receive based on county or state for local weather warnings; national advisories such as tropical storm and hurricane advisories are also available. For text messaging, you can even select a "quiet time" when you do not want to receive notifications. However, for urgent warnings such as tornado and severe thunderstorm warnings, we recommend setting these with 24-hour notification so that you can be alerted in the middle of the night. Sign up at http://www.weatherusa.net/alerts/