Unusual Severe Weather Outbreak over the Greater Phoenix Metropolitan Area on 28-29 August 2008

During the evening of 28-29 August 2008, an atypical severe weather outbreak occurred over and near Phoenix, Arizona. Between 8 pm MST (0300 UTC) and 1 am MST (0800 UTC), a succession of strong to severe thunderstorms propagated west-southwest across the metropolitan area. The combination of well-above-average storm motion and rapid regeneration of severe convective storms over and northeast of the metropolitan area was an extremely rare occurrence. In terms of impact, damaging straight-line winds, with peak gusts well in excess of 80 mph, resulted in widespread damage, with losses in the tens of millions of dollars, especially over central and south Phoenix, Tempe, and Mesa.

Anomalous atmospheric conditions for south-central Arizona, including strong low-mid tropospheric vertical wind shear and high thermodynamic instability, were observed prior to the outbreak, which heightened forecaster situational awareness and allowed WFO Phoenix to effectively convey the increased threat to our customers.

This paper will present a review of the circumstances under which this severe weather outbreak occurred, describe and depict convective storm evolution, highlight what went well and what could be improved with respect to outlook, outreach and warning operations, and focus on several ‘lessons learned'. Key information gleaned from real-time and post-event local and regional WRF model runs initiated the morning of 28 August 2008 will also be presented.