Arizona Desert Fall, Winter & Spring Temperatures; Flora & Fauna * FALL - Late September, October, November * October * Average high: 84.1°F (28.9°C) Average low: 56.5°F (13.6°C) Relative humidity at 5 am: 53% Relative humidity at 5 pm: 25% Normal rainfall: .79” (20.1mm) * Summer hangs on, with warm-to-hot days but cooling nights. It will freeze and most likely snow in the higher elevations. Some years might see unseasonable heavy rains this month, although this is uncommon. * Flora - Allergy sufferers bemoan the blooming of desert broom, a shrub that colonizes disturbed areas. However, broom flowers are a favorite of hundreds of butterflies, bees, wasps, and beetles. Many plants are fruiting, including barrel cacti, soapberry trees, desert hackberries, and wolfberries. Fall colors splash through canyons. * Fauna - Resident desert birds, or those that spend their winters here, are gorging on the many plant fruits. Most snakes head to winter burrows this month. One exception is the rosy boa, which lives in the warmer western deserts and will give birth this month and next. (Although most snakes remain fairly inactive in the colder months, keep in mind that they can emerge any time of year if enough warm days pass to sufficiently rouse them.) Wintering hawks arrive; common raptors include northern harriers, rough-legged and ferruginous hawks, kestrels, Merlins, and prairie falcons. Turkey vultures are mostly gone, but loud groups of common ravens replace them on carrion patrol. * November * Average high: 72.5°F (22.5°C) Average low: 45.2°F (7.2°C) Relative humidity at 5 am: 54% Relative humidity at 5 pm: 28% Normal rainfall: .59” (15.0mm) * Balmy weather finally begins to settle on the deserts, while winter grips the mountains. Expect mostly dry weather, although well over half a foot of snow may fall up high. Storms from the northwest may bring cold, even freezing, temperatures to the deserts as well. * Flora - Fall colors snake across low- and mid-elevation canyons where sycamores, cottonwoods, ashes, and walnuts begin to give up their leaves. Desert broom seeds take to the air in cloudy puffs that look like snow. Desert mistletoe berries begin to form. If many branch ends of mesquite trees begin to brown up and die, chances are mesquite girdler beetles were at work. The females bore a trough around, or “girdle,” a twig and then lay their eggs in the soon-to-die tips. * Fauna - Anna’s and Costa’s hummingbirds are the most common hummingbirds at feeders now; both will breed in the winter. Some Costa’s hummingbirds leave southern Arizona for the winter, returning in early spring to breed before the foresummer drought sets in. Although reptiles are mostly inactive, larger desert mammals such as bobcats, coyotes, badgers, and gray and kit foxes will remain active throughout the winter. Male desert mule deer rub the velvet off their antlers, which grew throughout the summer. Soon they will begin sparring with each other as they prepare for breeding competitions in the winter months.	* December * Average high: 65°F (18.3°C) Average low: 39°F (3.9°C) Relative humidity at 5 am: 61% Relative humidity at 5 pm: 34% Normal rainfall: .94” (23.9mm) * December is a mild month, with mostly cool but sunny days and only a few nights dropping below freezing, and possibly a few days of light winter rains. * Flora - Fruits of desert mistletoe, Christmas cactus, and netleaf hackberry trees are ripening, providing food for many birds and mammals. If winter rains begin, many shrubs such as brittlebush, creosote, and ocotillos will sprout bright new leaves, but many trees, such as mesquites, palo verdes, and sycamores, will drop their leaves as the temperatures dip below freezing. * Fauna - Birds in the Mimic-Thrush family, such as mockingbirds and curve-billed thrashers, begin to establish mating territories. They “map”territories by singing their famous copycat songs from the tops of trees, poles, or fences. Cactus wrens begin to build their breeding nests; they also build separate roosting nests—some pairs will build three or more nests. Anna’s hummingbirds may also breed this month. The males can be heard singing their squeaky songs around feeders. * January * Average high: 64°F (17.8°C) Average low: 38°F (3.3°C) Relative humidity at 5 am: 62% Relative humidity at 5 pm: 32% Normal rainfall: .86” (21.8mm) Normal snowfall: .31” (7.9mm) * In January, deserts will experience freezing temperatures half a dozen times, while up in the mountains it will freeze nearly every night and a foot of snow may fall. Desert days are mostly clear and pleasant, ranging from cool to warm; sometimes cold rains will arrive from the northwest. * Flora - At lower elevations, Frémont cottonwoods begin to sprout new leaves and open blossoms. If rain has been falling, many annuals and grasses will be sprouting new green growth. * Fauna - Mockingbirds, curve-billed thrashers, cactus wrens, and packrats (white-throated woodrats) begin their breeding seasons. Male phainopeplas—glossy black crested birds with white wing patches—perch conspicuously in palo verde or mesquite trees that are well-endowed with desert mistletoe berries, an important food source. They perform fluttery flight-displays to attract females. Mule deer breeding season, called the “rut,”is in full swing. Males engage in violent-looking but seldom injurious sparring with their antlers. Mountain lions feed well this month in the mountain foothills, where distracted male deer make easier prey.  * February * Average high: 67.5°F (19.7°C) Average low: 40.2°F (4.6°C) Relative humidity at 5 am: 59% Relative humidity at 5 pm: 27% Normal rainfall: .63” (16.0mm) * Winter is loosening its grip on the deserts; only a couple of nights may dip below freezing. Warm days tempt us later in the month with thoughts of spring—days in the 80s are possible—but cold snaps are still more probable. * Flora - Blooming shrubs may include chuparosa, samota, and desert mock-orange. Later in the month, if the fall and winter rains were generous, desert wildflowers may begin their show with such species as Mexican gold poppies, lupines, and owl-clover. In mountain canyons, deciduous trees such as alders and walnuts may bloom before they send out new leaves. * Fauna - Costa’s hummingbirds join Anna’s hummingbirds in establishing breeding territories around backyard feeders or blooming chuparosa shrubs. Male Costa’s hummingbirds display for females and mark their territories with a distinctive “zing” call. Rust-colored hummers that show up at feeders around mid-month are rufous hummingbirds, which are migrating through the Southwest. Gila woodpeckers hammer away at tree trunks or even metal pipes around buildings; they are marking their territories using sound. In the cool evenings or pre-dawn mornings, great horned owls can be heard calling softly, usually in duos, as they begin their breeding season. Pipevine swallowtail butterflies are common fliers this month.
May * Average high: 88.8°F (31.6°C) Average low: 57.4°F (14.1°C) Relative humidity at 5 am: 34% Relative humidity at 5 pm: 13% Normal rainfall: .15” (3.8mm) * May will likely see the first day over 100°F (38°F) in the desert; most days will be clear, dry and hot. Many animals, humans included, begin to retreat to the mountains, where balmy days and cold but not freezing nights beckon. * Flora - Many species of Cactus bloom nocturnally, including saguaros, senitas, organ pipes, and queens-of-the-night, also known as night-blooming cereus. Delicate lavender blossoms open on desert ironwood and smoke trees. Desert spoon and soaptree yuccas put up tall, woody bloomstalks with white flowerettes; desert spoon is dioecious, with male or female flowers. Many red, trumpet-shaped flowers are blooming in mountain canyons as hummingbirds become more numerous and continue breeding; among the most spectucular blossoms are those of the coral bean. * Fauna - Female nectar-feeding bats, many of which are pregnant, migrate from Mexico into desert areas where nocturnally blooming plants are flowering. The two species are Mexican long-tongued and lesser long-nosed, the latter of which are endangered; they give birth in colonial maternity caves. Gila monster eggs, laid ten months ago, begin to hatch; the young lizards are perfectly formed miniature versions of their venomous parents and immediately fend for themselves. In mountain canyons, red-spotted toads are mating, filling the nights with their loud trills.Balmy evenings around full moon are a great time to watch bats and moths visit cactus flowers. Don’t forget to watch for rattlesnakes and scorpions where you step or sit. *  June * Average high: 98.5°F (36.9°C) Average low: 67.3°F (19.6°C) Relative humidity at 5 am: 32% Relative humidity at 5 pm: 13% Normal rainfall: .24” (6.1mm) * Famously hot and dry characterizes June in the desert, with lots of days over 100°F (38°C)—and a few as high as 110°F (43°C) or more—and often not a drop of moisture. The high country will remain relatively cool, in the 80s even when the mercury climbs over the century mark down below. * Flora -Saguaro cactus fruits ripen, split open, and fall to the ground; many birds, insects, and mammals feed on them. Bean pods on mesquites, palo verdes, and catclaw acacias are ripening , as are jojoba seeds. If winter or early spring rains were plentiful, sacred datura may bloom. Organ pipe cactus continue to open their pale lavender blooms. * Fauna - Many snakes bear live young or lay eggs this month, including gopher snakes, common kingsnakes, Sonoran whipsnakes, and western diamondback and tiger rattlesnakes. Days are filled with the buzzing of male cicadas, also known as “cactus dodgers,”as the insects try to attract mates. Lesser nighthawks fill the warm nights with their unique trilling calls. This is a good month to see hawks that breed in riparian areas with tall cottonwoods or sycamore trees; look for gray, black and zone-tailed hawks, and Mississippi kites.	March * Average high: 71.9°F (22.2°C) Average low: 43.8°F (6.6°C) Relative humidity at 5 am: 53% Relative humidity at 5 pm: 23% Normal rainfall: .71” (18.0mm) * Spring begins in earnest in the desert, with warm and sunny days and cool nights; days are warming in the high country—enough to begin melting snow and filling creeks; we hear that magical sound of running water. * Flora - March is wildflower month. Look for dozens of wildflower species, including globe mallows, penstemons, evening primroses, desert marigolds, blue dicks, gilias, bladderpods, dock, chia, desert hyacinths, and many more. Many shrubs bloom as well, including desert lavender, hop bush, brittlebush, and Mormon tea. * Fauna - Many animals are breeding or preparing to breed. Elf owls arrive from wintering grounds in Mexico to breed in saguaro-mesquite desert; males arrive first and try to win females with their distinctive barking call as they perch in cavities in saguaro cacti or other trees. Burrowing owls and barn owls, which are also found in desert or even urban areas, also breed this month. Migratory songbirds begin to arrive, either to breed or to rest on their way to northern breeding grounds; riparian areas are especially good places to see them. Desert tortoises and desert box turtles emerge from burrows and begin to mate. Turkey vultures move back to southern Arizona for the summer. * April * Average high: 80.5°F (26.9°C) Average low: 50.1°F (10.1°C) Relative humidity at 5 am: 42% Relative humidity at 5 pm: 16% Normal rainfall: .31” (7.9mm) * Dryness begins to settle on the desert, with just a few days of possible sprinkles. Spring weather arrives in the mountains, with days in the 60s (>15°C) and only half the nights dropping below freezing. * Flora - The desert “bean” trees (legumes such as blue palo verdes, catclaw acacias, and mesquites) begin to open yellow to creamy blooms, and the cacti begin to bloom as well, with a few of the prickly pears, chollas, and hedgehogs starting off. By the end of the month, some saguaro cacti will open their big, white flowers. Brittlebush may still bloom; look for iron-cross blister beetles—they are black, yellow and red with black cross patterns on their backs—feeding on the brittlebush blossoms. * Fauna - Bird migration continues. Summer’s hawks, including Swainson’s, zone-tailed and Black hawks, begin to arrive and get busy finding mates for the summer breeding season. In mountain canyons around Tucson many hummingbirds arrive and breed, including broad-billed, black-chinned and magnificent. White-winged doves also return and fill the late-spring air with the signature summer call, “Who-cooks-for-you?”As the days lengthen and warm up, reptiles become more visible—time to watch for rattlesnakes (although remember they can be out any month of the year). Desert iguanas, lesser earless lizards and western whiptail lizards begin breeding. Bobcats, coyotes and foxes are having litters. And butterfly activity picks up; look for great blue hairstreak, hackberry, skipper, blue, and queen butterflies.
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