A massive desert sandstorm roared through Phoenix, Arizona last night, dropping visibilities to near zero and coating surfaces with a gritty later of dust and sand. The phenomena, known as a haboob, occurs when the outflow from a thunderstorm kicks up desert dust. Last night’s haboob was due to a large complex of thunderstorms known as a mesoscale convective system (MCS) that developed to the east of Phoenix.

As the outflow from the MCS hit the ground, large quantities of sand and dust became suspended in the air by 50 – 60 mph winds. The amount of dust was much greater than is usual for one of these storms, due to the large size of the thunderstorm complex, and the extreme drought conditions the region has been experiencing.

As the haboob hit Phoenix, winds gusted to 53 mph at Sky Harbor International Airport, and the airport was forced to shut down for 45 minutes due to visibilities that fell as low as 1/8 mile. The airport received only 0.04″ of rain from the storm, but large regions of Southern Arizona got 1 – 2 inches of rain overnight due to the monsoon thunderstorms. The Southwest U.S.’s annual monsoon season has kicked into gear this week, aided by moisture from Tropical Storm Arlene.

The welcome rains the monsoon’s thunderstorms will bring to the region should greatly aid the efforts of firefighters attempting to control the fires of the Southwest’s worst fire season in recorded history. The latest 5-day precipitation forecast from NOAA’s Hydrometeorological Prediction Center is calling for widespread areas of 1/2 – 1 inch of rain over Arizona and western New Mexico this week.