Today's Air Quality Forecast Discussion: The Phoenix-area air quality was again in the Good range for all pollutants on Saturday. The approach of a trough of low pressure from the northwest has helped to clear the air by providing some good mixing. High pressure to the southeast will hold its position this week, keeping that trough to the north of Arizona as it slowly advances east this week. Daytime highs across the Valley may reach 110°F on Monday, shaving a degree or two through the week, and eventually "cooling" to 105°F. Expect ozone levels to push back into the lower Moderate range by Monday and Tuesday under sunny skies. Particulates should hold in the upper part of the Good range. We do not anticipate any significant dust events this week.
Memorial Day's Air Quality
Forecast Discussion: Low pressure to the west will spin in place through much of the week. The southwest-to-northeast flow will keep the potential ozone and precursor train from southern California moving into Arizona. The good news is that smoke from southern California wildfires won't be much of an influence as crews have mostly subdued them. Local ozone levels continue to decrease steadily with highest levels in the lower Moderate range. With the churning trough of low pressure to the west, Arizona can expect gusty winds Tuesday and Wednesday. This could cause localized pockets of dust in the vicinity of recently disturbed soil. Overall maximum PM10 levels, however, should remain mostly in the Good range. Conditions improve Thursday as winds decrease.
Forecast Discussion: What an impressive dust event we saw Sunday morning. Contrary to some media reports out there, this was not a localized event. This was not a "dust storm". This was not isolated to Arizona. A large trough of low pressure moved through the western U.S. The leading edge of the cold front churned up an impressive amount of dust extending from the desert valleys of California and Nevada, through Baja, and finally northeast through Arizona and New Mexico. Looking at concentrations from monitors to the west, California was hit hard with dust first on Saturday morning. Around 10pm Saturday night, it was Las Vegas that got hit. Yuma saw concentrations spike around midnight. Then dust moved into the Phoenix area around 2 am on Sunday. The cold front continued east through the early morning hours, and by 11 am, levels and visibility improved significantly. About the same time our air cleared, Albuquerque, NM got slammed. This was a major dust event that could not be prevented on a local level no matter what control measures were in place. Nature vs. Man, and Nature won easily. As of 10am Monday morning, Phoenix-area PM10 levels are back in the Good range. Looking ahead, high pressure will move overhead this week, pushing daytime into the triple digits by Wednesday and Thursday. Unfortunately, we may see some more dust on Wednesday, this time from the east. Concentrations, however, should not result in an exceedance here in the Valley. Expect ozone levels to increase as well under sunny skies. The northeast and east winds could trap ozone and precursors in the Valley by mid-week, sending levels well into the Moderate range.
