PHOENIX - It seems like every afternoon during Monsoon we hear the word outflow being tossed around, but what is an outflow?
The term outflow quite simply refers to wind flowing out of a storm. How does an outflow form?
A mature thunderstorm has an updraft, air going up into the storm, and a downdraft, air coming down out of the storm.
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During monsoon in Arizona, the clouds can be 50,000+ feet tall. As the rain cools the air within the cloud, it begins falling toward the ground. Typically, when this air hits the ground it spreads out and an outflow is born.
Typically, outflows will move in the direction the storm is moving and can produce winds anywhere from 10 to 60 mph or more. Outlfows can also travel hundreds of miles.
The trick, however, is forecasting what each outflow will do.
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Possible outcomes:
Dust: When thunderstorms form over the open deserts, especially south and southeast of the Valley, outflow winds can kick up a tremendous amount of dust, producing the massive walls of dust we see each monsoon.
Create storms: Outflows are typically cold air, which is dense air, so as they move across the surface they can lift up the less-dense warm air ahead of them. As this happens, new thunderstorms can rapidly develop along the leading edge of an outflow.
Converge: If two or more outflows from different storms converge, they can form new storms within minutes. The classic pattern during monsoon is when storms are located to the north, east and south of the Valley. When these storms collapse, outflow winds move into the Valley from multiple directions and converge, creating thunderstorms across the region.
Enhance storms: If an outflow from a storm moves into an already developed storm, it can often enhance the severity of the storm.
Nothing: Sometimes the most frustrating case…outflows may move through an area and do nothing more than create a few wind gusts and change the wind direction.
Bottom line, outflows are often-times the main driver of storm development across the Phoenix valley and we closely watch all of them.
