Although the Arizona is mostly dry and temperate, sometimes it Pours for 30 minutes to an hour, and its is magical!
July-September Monsoon pattern rains can bring high winds, and an enormous amount of rainfall in a short period. While on the river in a boat, if you are lucky enough to experience a downburst of wind and rain, simply pull over on a beach, you are always safe on the shore, dawn your waterproof gear and settle in for a 30 minute down pour. https://www.kayakthecolorado.com/post/wind-on-the-river
After the system moves on you can get back on the water and shortly after that you will experience the most amazing miracle in the desert. Waterfalls ! If you could be so lucky to be on the river during one of these extreme events you will experience a magical transformation of the river ecosystem.
The Nuts and Bolts of our Monsoon system as explained by ASU's School of Geographical Sciences & Urban Planning
During the winter time, the primary wind flow in Arizona is from the west or northwest—from California and Nevada. As we move into the summer, the winds shift to a southerly or southeasterly direction. Moisture streams northward from the Pacific Ocean and the Gulf of Mexico. This shift produces a radical change in moisture conditions statewide.
Such a change, together with daytime heating, is the key to the Arizona monsoon. This wind shift is the result of two meteorological changes:
The movement northward from winter to summer of the huge upper air subtropical high pressure cells, specifically the so-called Bermuda High (H).
In addition, the intense heating of the desert creates rising air and surface low pressure (called a thermal low) in the Mohave (L).
These two features combine to create strong southerly flow over Arizona. The southerly winds push moisture north-ward from Mexico. Because Northerrn Arizona is a high elevation the Colorado Plateau is particularly blessed with these moist events. On any given day somewhere across the Colorado Plateau there is a moisture blessing providing important water to the otherwise dry high desert.
Storm cells in Arizona are generally short-lived. There are three basic stages of thunderstorm development: the updraft cumulus stage, the mature stage and the dissipating stage. The lifecycle of a thunderstorm cell going through these stages is, on average, about 30-40 minutes.
The first stage of thunderstorm development is the updraft (cumulus) stage. In this stage, the primary activity within the cell is pronounced vertical uplift. Warm moist air is lifted adiabatically and condenses to form cumulus-type cloud formations. As the updraft stage continues, the formation of towering cumulus begins. Little or no precipitation occurs during this stage.
The second stage of thunderstorm development is the mature stage that is characterized by both updrafts and downdrafts. Downdrafts are associated with air that is pulled downward by precipitation. Normally downdrafts will be found near the leading edge of the thunderstorm cell. The air descending from the thunderstorm will often hit the ground and be forced out ahead of the cell creating a gust front. In the Arizona desert region, these gust fronts will pick up large quantities of dust and/or sand creating a dust wall. The common desert term for such a phenomenon is haboob.
Downburst. Localized pockets of intense downdrafts can create severe weather conditions called "downbursts" . A "downburst" is a strong downdraft that induces an outward burst of damaging winds on or near the surface. Downbursts can be large, called a "macroburst" (2.5 miles or large outflow diameter and damaging winds lasting 5 to 20 minutes) or small, called a "microburst" (less than 2.5 miles outflow diameter with peak winds lasting only 2 to 5 minutes). Therefore, "macrobursts" and "microbursts" are severe conditions of downdrafts.
All downbursts are characterized by a circulation termed a "vortex ring", a vertically rotating circle of air. Downdrafts can be dry or wet. A dry "downburst" is more common during the climatologically drier times of the Arizona monsoon (June & early July), while a wet "downburst" prevails during the wetter times of the monsoon, statistically in late July through September.
Dry downbursts will not necessarily show a solid perturbation from the base of the cloud to the characteristic curl. Instead, a dry downburst is generally only visible when the vertically descending winds hit the ground and pick up substantial quantities of dust. These types of downbursts are common in Arizona and will be particularly evident during the early portion of the monsoon season when there is still little precipitation associated with thunderstorms.
Wet downbursts, on the other hand, have the characteristic precipitation curl tracing out the vortex-ring circulation that surrounds the concentrated downdraft within the rain shaft. Most wet downbursts will describe a "foot shape" as the strong vertical winds carrying precipitation hit the ground and curl upwards.
Flash Floods on the River:
Never hike in side canyons when there is a possibility of rain. Storm clouds, and thunder are a sure sign the possibility of a flash flood exists. Flash floods are floods that can engulf a canyon in minutes and injure the unprepared hiker. Stay out of the Side Canyons if there is any chance of rain. If you see water in a normally dry riverbed get to high ground, there may be a wall of water coming your way. After you determine the flood has passed or the danger will not come, make a quick exit. Flash floods kill people every year in Arizona, it need not happen. Never enter a side canyon when you hear thunder, or experience dark clouds.