Hot, humid, hazy weather gives way to rain chances after the weekend
There are a few more days of high heat to get through during the weekend of Aug. 7-9, but next week, the monsoon brings rain chances to metro Phoenix.
- Powerful dust storms rolled through metro Phoenix late Monday, Aug. 3 and early Thursday, Aug. 6. Both storms were graded category 5 by the new PHX-Dust Scale.
- Dust storms can happen back-to-back, but they’re not usually both of such high intensity. They’re the second and third strongest since records began 16 years ago.
- Looking forward, dust storm chances decline as monsoon storm chances reenter the forecast next week.
If you were in metro Phoenix this past week, you already know about the hazy skies. They’re now a big part of history.
The two powerful dust storms that rolled through the Valley late Monday, Aug. 3 and early Thursday, Aug. 6 were both declared category 5 dust storms — the latest two out of the now six total — and the first time, in at least 16 years, that dust storms of this intensity have struck back-to-back. They’re the second- and third-strongest dust storms on record, respectively.
The category 5 rankings come from the new PHX-DUST Scale developed by Arizona State University’s School of Geographical Sciences and Urban Planning. It’s a ranking system that determines strength primarily by how dense the dust was, as well as how long the storm lasted, how far it spread and how strong the winds were.
How strong is category 5?
A category 5 storm is defined as an “extreme dust concentration” of at least 5,000 µg/m3 (micrograms per cubic meter) of PM10. particulate matter that includes coarse solids like dust.
The Aug. 3 storm reached 6,136 µg/m3 in St. Johns on the Gila River Indian Community, and the Aug. 6 storm peaked at 5,841 µg/m3 in Chandler. Both received a “WLH” tag, signifying (w)idespread impact, (l)ong term duration and (h)igh wind speeds near 40 to 50 mph.
Visibility also dropped under a mile during both events and air quality was at unhealthy to hazardous levels the mornings after. Both subsequent mornings had high pollution alerts issued by the Arizona Department of Environmental Quality.
Are back-to-back dust storms rare?
It’s not uncommon to have successive dust storms since it’s dependent on overall weather patterns, which tend to last days at a time. It’s the strength of each that’s so impressive.
During the week, monsoon storm chances were consistent in southeastern Arizona while it stayed dry near Phoenix. Strong outflow boundaries from those storms kicked up dust in Pima and Pinal counties and shoved it all into Maricopa County. Dust storms can happen more commonly during long stretches without rainfall, which has been the case in the Valley since mid-July.
When will it rain in metro Phoenix?
Conditions are expected to remain dry with high humidity through the weekend as high pressure remains overhead, but forecasts show a shift that will allow better chances for scattered monsoon thunderstorms next week.
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Meteorologist Tevian Whitehurst covers extreme weather and climate for The Republic and azcentral.com. Follow him at @TevianWX on Instagram and Facebook (Meteorologist Tevian Whitehurst).