During early December of 2004, staff at the Albuquerque (ZAB) Center Weather Service Unit (CWSU) received several Pilot Reports, or PIREPS, describing a layer of elevated haze over the Phoenix airport. Haze at the surface can restrict visibility, but during several days of the winter season of 2004-2005, PIREPs noted elevated haze at time when the surface observation did not include haze or a reduction in visibility. When haze is present aloft, slantwise visibilities through the haze layer can be noticeably reduced, affecting the approach phase of aircraft and reducing the acceptance rates.

A study was initiated with the goal of identifying significant parameters that can be responsible for slant range visibility problems due to haze in Phoenix. The results of the study are available in pdf format.

Several cases of elevated haze were documented during the winter of 2004-2005, and several are discussed in the paper describing the results of the study listed above. It was anticipated that the results would help staff at the CWSU with forecasts of elevated haze. However, during the winter season of 2005-2006, no PIREPs reporting elevated haze were received. In the figure below, average relative humidity at 700mb is displayed for the period December 1, 2004 through February 28, 2005 (left panel) and for the same period one year later (December 1, 2005 through February 28, 2006, right panel). Note that winter 2005-2006 had much lower average 700mb relative humidity. A similar plot of the anomalies verifies that while the winter of 2004-2005 was slightly more humid at 700mb than normal, the winter of 2005-2006 was much drier than normal. In the drier atmosphere, the development of haze is less likely. Plots for the 850 mb surface indicate a similarity in both the average relative humidity as well as the departures from the long term mean.