Did you know that Southern Arizona has 5 seasons? Yes, it actually has 2 short summers.
Winter - Late December to Late February
Southern Arizona winter is not like Florida's Winter. From December through February you may experience temperatures from 19°F in early morning to 80°F at the end of the day, probably not on the same day. However, 32° in the morning and 70° in the late afternoon is not unheard of. From late December through February you may experience rain. This is usually the Oregon type rain, and on occasion you will get a good windy storm from the west. This past year, 2018, was unfortunately mostly dry. Only one freeze in Tucson, a bit colder in Bisbee. You know it is winter by the appearance of the Sandhill Cranes on the Willcox Playa, and spring is coming when they fly back north.
Spring - Mid February to Late April
One word. Beautiful. That is what all the snowbirds think too. By late April, Southern Arizona is left to the full year residents, and hummingbirds, some of which are here all year.
Dry Summer - May through June
This is generally the hottest time of year. May and June can be brutal. Things quiet down. One plus is the night, yes one night, that the "Queen of the Night" Night Blooming Cereus blooms. Expect temperatures above 100° F most days. If you haven't got tomatoes by now, go to the store, you will wait until September - October to get started again. With two short growing seasons, the big ones are a challenge to grow. Visit the Mission Garden for a tour. They are open Saturdays from 8-noon.
Wet Summer (Monsoon) July - September
The Tohono O'odham celebrate the beginning of the rainy season on the Feast of San Juan, (John the Baptist) on June 24 each year. The Fiesta de San Juan takes place at the Mercado San Augustin each year. The Mercado is near A Mountain, (Sentinal Peak). As the Monsoon weather builds to a head, the humidity goes up. Get ready for some Florida like days until the rains come.
Fall - October Through / Mid December
Fall is my favorite season. It is usually longer than spring, and if it is short, it does not lengthen the Summer. The first year that we moved here, It was 80°F on Thanksgiving Day. The windows were wide open. The nights have cooled off and the mornings can be brisk. Most years I get roses through December in my garden.
Be sure to read: So what's the weather like in Southern Arizona?