The Southwest monsoon season kicked off June 15 and is wasting no time getting underway, as early-season monsoonal moisture surges into the region and brings the threat of thunderstorms capable of producing flash flooding.
This increase in moisture first spread across Arizona and New Mexico, then work its way north into the central Rockies. As the ground heats up, thunderstorms are expected to fire up each afternoon before diminishing in the evening as the sun goes down.
Many of these storms will be potent with heavy rainfall rates. Flash flooding will be possible in any areas that get drenched by thunderstorms across the Southwest and the central and southern Rockies.
NOAA's Weather Prediction Center has highlighted this region as having a risk of excessive rainfall through Sunday evening. Areas most prone to flash flooding are near residual burn scars across the Four Corners region and northward into southern Wyoming.
Meanwhile, some thunderstorms may not contain much rainfall in parts of the Great Basin, resulting in dry thunderstorms. These storms could ignite other wildfires in parts of southwestern Wyoming, eastern Utah and into the heart of the Four Corners region.
There is a critical risk of fire weather from the central Great Basin southward into the lower Colorado River Valley on Friday, as well as an elevated risk in the central High Plains. These same areas are expected to have a continued threat of fire weather into at least the first half of the weekend as strong winds, low humidity levels and dry fuels are forecast to persist.
Monsoon season in the Southwest
The Southwest monsoon season begins June 15 and lasts through Sept. 30 each year.
Monsoon is a term given when winds blow tropical air toward typically desert locations, and Arizona and the Desert Southwest certainly qualify.
According to the National Weather Service, a ridge of high pressure in Mexico blocks any moisture from reaching the Desert Southwest in early June, allowing for days of hot, dry weather. Later in June and into July, the ridge drifts north into the Four Corners region of the U.S., allowing some tropical moisture to be carried northward from the Gulf of California and the Pacific Ocean.
Combine the desert heat with the copious amounts of tropical moisture, and you have a setup ripe for strong thunderstorms with torrential rain. What's more, northern Arizona is home to the Mogollon Rim, an area of high elevation that can provide the additional lift needed to trigger the development of thunderstorms that will often drift into the Phoenix area.
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