A new classification system for dust storms, including haboobs, is being used in the Phoenix area as the monsoon ramps up. This category-based system was developed by Arizona State University researchers in an effort to standardize the ranking of these events, which historically has never been done.

What is the dust storm scale?

The Phoenix Dust Storm Scale assigns categories to each event, which fills a longstanding gap. Despite how common and disruptive dust storms are to transportation and public health during Arizona's monsoon, there was previously no standardized way to quantify or compare them.

The scale allows for consistent communication of the severity of these storms, better public awareness of impacts and standardized data for research and understanding of the events.

How the rating works

Similar to the Saffir-Simpson wind scale used to classify hurricanes, the dust storm scale uses a 1-to-5 classification system with Category 1 being minor and Category 5 being extreme.

The storms are evaluated using multiple factors, including particulate matter (essentially the amount of dust in the air), geographic extent, duration and wind gust speed.

It is important to note that the dust storms are classified after they are over, similar to how the Enhanced Fujita (EF) scale is used for tornadoes, based on observational data.

As shown in the graphic below, the primary rating comes from the dust's concentration, but the other factors come into play as sub-categories:

• Geographic extent: The storms can be labeled either Widespread (W) or Isolated (I), depending on the number of monitoring stations that report a dust concentration of a certain threshold. Widespread means over 50% of the stations reached this marker, while Isolated means it was less than half of the stations.
• Duration: Depending on how long the storms last, they can be classified as either Long-Duration (L) or Short-Duration (S). Events longer than three hours fall into the first sub-category while events shorter than three hours fall into the latter.
• Wind gust speed: Storms with measured wind gusts above 25 mph are classified as High Wind Gust (H) events.

Let's use an example.

If we were looking at the notorious Phoenix dust storm on July 5, 2011, it would be considered a "Category 5 WLH" (widespread, long-duration, high-wind).

Dust storm or haboob?

"Dust storm" is the general, catch-all term for any event where strong winds loft dust particles into the air, reducing visibility and air quality.

Meanwhile, a haboob is a specific type of dust storm that happens as a result of the downdraft or outflow winds from a collapsing thunderstorm.

So, all haboobs are dust storms, but not all dust storms are haboobs.

Phoenix sees these frequently during the Southwest monsoon, which typically runs from June through September, because of the thunderstorm activity and strong winds.

(MORE: America's monsoon has a big impact on the Southwest)

Caitlin Kaiser graduated from the Georgia Institute of Technology with both an undergraduate and graduate degree in Earth and Atmospheric Sciences before starting her career as a digital meteorologist with weather.com.