When does Monsoon season start? What causes Monsoon?

The official start date of the Arizona Monsoon season is June 15.  In 2008, the National Weather Service determined the AZ Monsoon starting date along with the ending date of September 30.

Tucson Phoenix Monsoon weather
storm clouds Monsoon season

What causes monsoon?

Traders sailing the Indian Ocean and Arabian Sea used the word monsoon to describe a system of alternating winds which blow from the northeast during the northern winter and from the southwest, during the northern summer. Therefore, the term monsoon refers solely to a seasonal wind shift, and not precipitation.

Mexican monsoon cloud
Arizona Mexico Border storm clouds

Arizona happens to be located in the area of the United States that experiences a monsoonal circulation. During the summer months, winds shift from a west or northwest direction to a south or southeasterly direction.

Monsoon weather for Arizona
Microburst clouds during Monsoon

This wind shift allows moisture from the Gulf of California and the Gulf of Mexico to stream into Arizona.  A monsoonal circulation produces a radical change in moisture conditions throughout the entire state.

Arizona thunderstorm dark clouds
Monsoon storm clouds over Coronado Mountains

Thunderstorm or cumulonimbus clouds are very familiar during monsoon season.  These storm clouds cause lightning, hail and heavy rain.

Arizona desert Monsoon Storms
dark thunderstorm burst clouds

What Arizona experiences during the summer months is only a small part of a larger circulation that encompasses much of the southwestern United States and northwestern Mexico. Thus, it sometimes is also known as the Mexican monsoon. The National Weather Service calls it the North American Monsoon.

microburst monsoon storm cloud
Monsoon clouds Mexican Arizona Border

This adjustment in wind direction is the result of two meteorological changes:

  1. the movement northward of the huge upper level subtropical high pressure system, known as the Bermuda High,
  2. and the intense heating of the Mohave Desert creating rising air and surface low pressure, called a thermal low
severe dark thunderstorm cumulus cloud
Monsoon Storm clouds on top of mountains

The southerly low-level winds help to bring in moisture from Mexico. When this moisture encounters the higher terrain of Arizona mountain ranges, it gets lifted and forms thunderstorms.

dark storm Clouds on arizona border
Monsoon storm Coronado Mountains

Small driving factors such as: atmosphere interaction, land elevation, soil moisture and vegetation all play a part in what drives the Arizona Monsoon; but it is also why predicting storm intensity is so difficult.

When such high volume rain descends upon the Arizona desert the ground and the surface streets flood. Quite often the rain pools on streets during monsoon storms causing dangerous driving conditions.

cumulus thunderstorm cloud
Storm burst clouds at Arizona Mexico Border

The monsoon circulation does not produce thunderstorms every day during the summer months, but rather monsoon storms occur in a pattern known as “bursts” and “breaks”.

best Microburst storm cloud photo
Monsoon microburst cumulus cloud

This cycle of bursts and breaks will continue from the onset of the monsoon (typically June), until the time when cold fronts begin to move across the state of Arizona (typically September), which will return our winds to a westerly or northwesterly direction.

We hope you enjoyed this article.  Our goal was to make Monsoon Season easier to understand.

Interesting Saguaro Cactus Facts

One of Arizona’s most majestic, lovable desert cactus plants is the Saguaro, Carnegiea gigantea. Being aware of the saguaro’s history and incredible internal design, it is an honor to walk close to the Giant Saguaro that is over 150 years old and standing tall.

Sonoran Desert cactus tall
Giant Saguaro Cactus of Arizona

These desert cacti are large, tree-like columnar cacti that develop branches (or arms) as they age.

Saguaro Cactus can not tolerate freezing temperatures in the winter and this is what limits their range.

Saguaro National Park
Saguaro Cactus

Saguaro FACTS:  Saguaros are a very slow growing cactus.  A 10 year old plant might only be 2 inches tall.

How tall can a Saguaro Cactus grow?  It can grow 40 to 60 feet tall.

Arizona Saguaro Giant Cactus
Saguaro Cactus on Mica Mountain
60 foot Saguaro Cactus plant
A Tall Saguaro Cactus

Below are Saguaro cacti at the bottom of Mica Mountain in Saguaro National Park.

Mica Mountain Saguaro National Park

Saguaro cactus roots are only 4-6 inches deep and travel out as far from the plant as it is tall. There is one deep tap root that extends down into the ground.

A Saguaro Cactus can gather enough water through its remarkable root system, during a significant rain, to last a year!

holes in big cactus
Holes in Saguaro Cactus for birds nest

Why are there holes in the Saguaro Cactus?  The gilded flicker and Gila woodpecker excavate nest cavities inside the saguaro’s pulpy flesh.

Birds nesting in the Arizona Saguaro Cactus

Cactus Wrens are common birds that live in the holes (nests) of the Saguaro Cactus.

red fruit of cactus
Saguaro Cactus Flowers bloom, then turn to fruit

When a saguaro reaches 35 years of age it begins to produce flowers.

white flower on cactus arizona
Saguaro cactus Bloom – Flower

A Saguaro can only be fertilized from a different cactus – cross pollination.  Only a few bloom each night awaiting to be pollinated and close by late morning.

pollinated cactus flower to fruit
red fruit on Saguaro Cactus
dead saguaro cactus ribs
A living and dead Saguaro Cactus.

Because the major part of a desert saguaro cactus is made up of water, an adult plant may weigh 6 tons or more. This tremendous weight is supported by a circular skeleton of inter-connected, woody ribs.

After the saguaro dies its wood ribs can be used to build roofs, fences, and parts of furniture.  The holes that birds nested in are called saguaro boots.

holes in cactus in Arizona
Saguaro Boot used by Native American

Native Americans used saguaro boots as water containers.

200 year old tall saguaro cactus
Saguaro Cactus next to a biker to compare the size

Saguaro branches normally begin to appear when the cactus reaches 50 to 70 years of age.

The average life span of a saguaro is approximately 175 years of age.  Experts have estimated that a Saguaro Cactus with more than 5 arms can be 200 years old.

nurse tree for saguaro cactus
Yellow Palo Verde Tree is a nurse tree

Young saguaro cacti can be very hard to find because they grow under the protection of a “nurse tree”.  The nurse tree releases nitrogen in the soil which the Saguaros and other desert cacti use to grow healthy and strong.

Saguaros sometimes grow in odd shapes or forms. The growing tip of the cactus occasionally produces a fan-like form which is referred to as crested or cristate.

rare arizona cactus
Cristate Saguaro Cactus

These crested saguaro cacti, Carnegia gigantea forma cristata, are rare.  Biologists are not sure why these Saguaros grow this fan-like shape.

Fan like shaped cactus rare
Crested, Cristate, Fan-like Saguaro Cactus from AZ
crested cristate cactus in Tucson Phoenix
rare Saguaro in Tucson

Arizona has strict regulations about the harvesting, collection or destruction of  The Arizona Saguaro Cactus. It is illegal to harm a Saguaro in Arizona. During building or construction, precautions must be taken to move every saguaro that may be affected.

Arkenstone Cave in AZ – Protected living cave at Colossal Park

Arkenstone Cave was discovered near the Rincon Mountains of Southeastern Arizona in the 1960’s.  This living cave is protected by the county and accessible only to a few scientists and researchers.

wet live cave in Arizona
Arkenstone Cave in Arizona

We have spent a great deal of time investigating information regarding Arkenstone and La Tetera Caves.  Our most important finding has been the fact that Pima County regards these living caves as treasure troves of precious, immeasurable scientific information.

Access is extremely limited; but a visit to Colossal Cave Mountain Park Museum can provide the curious with results of the past and latest research conducted inside Arkenstone Cave.

Here are some of the research highlights provided from the Museum Caving Rooms at Colossal Cave east of Tucson, AZ.

Colossal Cave Mountain Park
Arkenstone Cave is used for research

ARKENSTONE is an active KARST CAVE, which means the breaking down of limestone has produced fissures, sinkholes, caverns and underground streams.

Most caves are formed in limestone.  Simply put, it dissolves from precipitation mixing with carbon dioxide and the decaying organic material in the soil.  This dissolution process is extremely slow.  Thousands upon thousands of years!

Arkenstone karst caves
Karst diagram, Limestone Caves

Karst image courtesy of  www.geocaching.com

Arkenstone, La Tetera and Colossal Caves are located in Colossal Cave Mountain Park, Arizona.  Colossal Cave is dry and considered a dead cave.  La Tetera and Arkenstone are alive and adorned with calcium carbonate formations produced through slow precipitation.

SPELEOTHEMS in Arkenstone Cave
Arkenstone Cave Crystal formations

Mineral deposits in caves are called SPELEOTHEMS.

ARKENSTONE CAVE is called:

  • a WILD cave
  • a WET cave
  • a LIVE, “active” cave

What does this mean… A wild cave has no provisions for the general public and is dangerous without expert equipment and experience.  A wet cave has precipitation.

Colossal Cave Mountain Park Caves
Tower Coral, crystal formations on the floor of Arkenstone Cave

A live cave has life forms, insects, faunal, animal, species and unusual speleothems.

Pima County and Colossal Park employees have an overwhelming desire and responsibility to protect La Tetera and Arkenstone living Caves.

research caves protected in Pima County
species found in Arkenstone Cave, Colossal Mountain Park, AZ

Several new species have been found in Arkenstone that are endemic to Arkenstone, meaning they only exist in Arkenstone Cave.  A few researchers have special grants to work in these living Arizona Caves.

In recent years, 7 new species of fauna have been found.  The Arkenstone Cave exhibit at Colossal Mountain Park Museum gives detailed descriptions.

Arizona Wet Caves, Arkenstone
research at Arkenstone Cave

Animals that live in caves are often put in the category called TROGLOBITESTroglobitic species tend to be very unusual organisms.  For example, they may have loss of pigment or no eyes.  These characteristics would be adaptations to their subterranean life.

live caves in Arizona
Pseudoscorpion found in Arkenstone Cave

A previously unknown species of pseudoscorpion was discovered in Arkenstone.  The pseudoscorpion has since been listed as one of Pima County’s priority vulnerable species!

vampire bats in Arkenstone Cave
Bat Bones found in Arkenstone Cave

A small, late Quaternary, (about 2 million yrs ago), deposit of degraded bat guano (poop) in Arkenstone Cave yielded thousands of fossil bat bones.

Colossal Park living caves, La Tetera Arkenstone
Arkenstone Cave Exhibit and research

Rarer bones in the deposit represent a smaller species of bat (Myotis) and the extinct vampire bat Desmodus stocki.

This is the first record of D. stocki in what is now the Sonoran Desert and the second location for the vampire bat species in Arizona.

Rincon Mountains Arkenstone Living Cave
Extinct Vampire Bat found in Arkenstone Cave

Due to leaching in the alkaline cave environment, the bones could not be dated by radiocarbon, but the fossils probably date to the late Pleistocene Age  —  (Late Pleistocene Bats from Arkenstone Cave, Arizona by Nicholas Czaplewski and William Peachey, December 2003)

The Late Pleistocene age was dominated by glaciation  Many larger land animals, MEGAFAUNA, became extinct over this ICE AGE.  Experts estimated that 30% of the Earth’s surface was covered by ice.  Pleistocene vampire bats most likely were capable of surviving in cooler temperatures than the modern bats of today.

The extinction of Desmodus stocki paralleled the extinction of the megafauna.

Pleistoncene Ice Coverage on Earth
Photo of Earth during the Ice Age, The Pleistocene

Research indicates that Arkenstone Cave was the site of a maternity colony of Myotis thysanodes.  Myotis thysandoes is a larger species of bat, mammal.  These bats begin nursing colonies, female nurse bats remain at the roost while other adults are out foraging.

Arkenstone, La Tetera Cave Arizona
extinct vampire bat, Desmodus stocki

Virtually all of the bones collected were of that species.  Remains of Desmodus are consistent with a single individual, and those of a small Myotis (bat) consistent with two individuals (Czaplewski and Peachey 2003).

altruistic example, bats
Arkenstone Cave discovery of extinct vampire bats

Desmodus stocki was 20% larger than the still extant common vampire bat.   Lets put aside the scary name, VAMPIRE, and let me share some benevolent behavior of Vampire Bats that may gain your admiration for the Pleistocene bat, Desmodus Stocki.

Vampire Bats are one of the few animal species that show caring behavior for those beyond their family group.  They even adopt orphaned bats and will share their food.  Look at the photo above for more altruistic vampire ways.  🙂

vampire bats, Arkenstone Cave
common vampire bat skull, teeth

Scientists state that fossil records of Desmodus stocki are uncommon because these bats mainly roosted in hollow trees and any remains would decay along with the wood.

Arkenstone Cave Arizona
new species found in Arkenstone and Kartchner Caves

photo above is courtesy of  Journal of Cave and Karst Studies

A new species of Nicoletiidae (Insecta: Zygentoma) has been discovered in Arkenstone and Kartchner Caves.  This species pictured above lives in deeper areas of Arkenstone Cave than it does in Kartchner.
The 2 caves are approximately 23 miles apart and in isolated Karst areas with no possible connection to each other.
Rincon Mountains Caves Arizona
Caves at Colossal Cave Mountain Park
You would think that these would be different species?  But so far the research shows they are the same.  How amazing is that?
caves at Colossal Mountain Park in Vail AZ
Arkenstone Cave
Cave species are very fragile and some live in a specific cave and no where else in the world.   These TROGLOBITES are accustomed to a near constant temperature and humidity.  Even the slightest disturbance can disrupt the life cycles of these amazing species.
Arizona active wild caves, Arkenstone
Crystal formations in Arkenstone Cave
As updated research becomes available we will add new articles.
fringed myotis is found across the western United States.
The fringed myotis is found across the western United States. It has been found as far east as the Trans-Pecos region of Texas during summer months, as far north as British Columbia and as far south as Mexico.
The fringed myotis is found across the western United States. It has been found as far east as the Trans-Pecos region of Texas during summer months, as far north as British Columbia and as far south as Mexico.