84th AMS Annual Meeting

Monday, 12 January 2004
Severe weather outbreak over Phoenix, Arizona, on 14 July 2002
Room 4AB
G. Douglas Green, NOAA/NWSFO, Phoenix, AZ; and E. S. Pytlak
Poster PDF (2.6 MB)
Severe weather affected numerous locations over south central and southeast Arizona the afternoon and evening of 14 July 2002. Phoenix, Arizona, was the unfortunate recipient of 3 varieties of severe weather: 1) a major haboob (dust storm accompanied by 18-29 m/s (40-65 mph) straight line wind) affected much of the greater Phoenix area between 0245 and 0425 UTC 15 July; 2) damaging microbursts, with winds in excess of 45 m/s (100 mph), struck Sky Harbor International Airport between 0320 and 0345 UTC, and caused an estimated $70M in damage to buildings, aircraft, and motor vehicles; and 3) flash flooding, triggered by rainfall rates occasionally in excess of 15 cm (6")/hour and rainfall totals exceeding 5 cm (2")/hour, occurred over central Phoenix between 0345 and 0445 UTC. While dust storms, microbursts, and flash floods frequently occur over southern Arizona during the summer convective season, it is rather unusual to have extreme versions of all three phenomena occur in close spatial and temporal proximity. This paper provides a synoptic scale overview, then details the evolution of the severe weather event, especially over Phoenix, paying particular attention to mesoscale and microscale features associated with the Sky Harbor microburst(s) and central Phoenix flash flood. Localized forcing associated with deep cold pool outflows, colliding cold pool outflow boundaries (OBs), and interaction between OBs and a pre-existing convergent zone are shown to be critically important with regard to severe weather mode and location.

The SPC (Storm Prediction Center) provided excellent guidance (collaboration calls, watch box issuance, mesoscale discussions) to the local WFOs for this event. A detailed assessment of the quality and usefulness of guidance products issued by SPC and the local WFOs is included in this paper. As is ususally the case over the lower desert of south-central Arizona, the degree of threat and likely location of the most dangerous weather was not easy to assess with much lead time; an HWO issued by WFO Phoenix accurately assessed the threat and most likely location of the severe weather, but provided less than 3 hours' lead time to local emergency management, media outlets, and other customers. The HWO's content and issuance time was predicated to a great degree on observed mesoscale development, some expected (intense thunderstorms over and near Tucson) and some unexpected (strong/severe thunderstorm development north of Phoenix).

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