Deadly 'fungal storm' heads toward major US cities today as officials warn residents to stay indoors

 A dangerous dust storm will sweep across Arizona in just hours, potentially filling the air with harmful fungal spores that can cause a deadly illness.

Hundreds of thousands of residents in the central and southern parts of the state are in the path of the so-called 'fungal storm,' triggering a blowing dust advisory from the National Weather Service on Wednesday.

Wind gusts of up to 55mph are expected to blow thick clouds of dust, debris and soil through cities such as Phoenix and Tucson between 6pm and 1am ET (3pm to 10pm local time).

The storm is expected to mainly affect parts of Maricopa, Pinal, Pima and Santa Cruz counties, including the Phoenix-area suburbs of Buckeye, Avondale, Ahwatukee and Queen Creek. Roughly 1.5 million people are in the path of the dust advisory.

NWS has warned that visibility, especially for drivers, will be cut to just one-quarter of a mile on Wednesday, making travel potentially hazardous throughout the night.

Another concern during an Arizona dust storm is the microscopic fungus called Coccidioides, which is blown into the air from local soil and can trigger the potentially fatal lung infection Valley fever when inhaled.

NWS warned in a statement: 'Persons with respiratory problems should make preparations to stay indoors until the storm passes. Be ready for a sudden drop in visibility to near zero.'

Arizona officials have not confirmed that the dust storm will contain the fungus, but the CDC has warned that Coccidioides is found throughout all of Arizona and its neighboring states in the Southwest

NWS added that conditions throughout Arizona on Wednesday, including the chance for severe thunderstorms and high winds, will make it possible for a phenomenon known as haboobs to form.

These are huge walls of dust kicked up from the dry ground right when the soil is at its driest. The combination of extreme heat and drought plus monsoon winds create more frequent and intense dust storms carrying Coccidioides.

For people caught outside during a fungal storm, the spores turn into growing fungal cells that the immune system typically fights off, causing mild flu-like symptoms such as fever, cough and headaches in most patients.

However, severe infections can spread to the organs and bones and become fatal. The CDC has warned that between 15 and 30 percent of all cases of pneumonia in the Phoenix and Tucson areas are caused by breathing in Coccidioides. 

NWS warned that individuals suffering from heart disease and chronic respiratory conditions such as asthma will be among those at the greatest risk for complications.

'Those most at risk may feel better if they avoid outside exercise today, keeping windows and doors closed to help reduce exposure,' the weather agency added.

Those driving through Arizona have also been warned to be ready for potentially fatal road conditions, as blowing dust can make it impossible to see anything within seconds.

'If you encounter blowing dust or blowing sand on the roadway or see it approaching, pull off the road as far as possible and put your vehicle in park. Turn the lights all the way off and keep [your] foot off the brake pedal. Remember, "Pull Aside, Stay Alive,"' NWS advised in their alert.

At the same time as the dust and thunderstorms, an Extreme Heat Warning has been issued throughout the same parts of central and southern Arizona through Friday.

Temperatures are expected to compound breathing issues outside, with the heat index approaching 110F.

The heat index is the 'feels like' temperature, which is hotter when the air is more humid. On a 90-degree day, high humidity can make the 'feels like' temperature reach 105F.  

'Overexposure can cause heat cramps and heat exhaustion to develop and, without intervention, can lead to heat stroke,' NWS said.

The extreme forecast is being fueled by a massive heat dome, a system of high pressure, blanketing the western half of the US. The pressure traps heat and humidity close to the ground like a lid on a boiling pot.