Moisture increasing in Southern Arizona as we head into the workweek

Tucson will begin the workweek with sunshine, temperatures in the mid 90s and only a small chance of rain, but moisture is expected to build across Southern Arizona over the next several days. The immediate forecast calls for isolated showers today and Monday, followed by somewhat better chances beginning Tuesday. For people commuting, working outdoors or planning evening activities, the main change will be a gradual increase in humidity and the possibility of storms developing nearby, especially south and east of the city.

Today’s forecast calls for mostly sunny skies with some clouds, a high near 96 degrees and a 10 percent chance of rain. Winds higher in the atmosphere are shifting from west to southwest, a pattern that will begin pulling additional moisture into the region. Tonight should be mostly clear, with temperatures dropping to around 72 degrees. Monday is expected to look similar, with a high near 96, mostly sunny conditions and another 10 percent rain chance.

The forecast becomes more active Tuesday, when Tucson has a 20 percent chance of showers and thunderstorms and a high near 95. Tuesday night also carries a 20 percent chance of showers, with partly cloudy skies and a low near 72. The wettest areas are not expected to be evenly distributed. Storm chances are forecast to be strongest south and east of Tucson, while the city itself is expected to remain closer to a 20 percent chance.

By midweek, deeper moisture is projected to reach Southern Arizona, bringing shower and thunderstorm chances back into the daily forecast. Wednesday is expected to have a high near 93 and a 10 percent chance of showers and thunderstorms during the day and at night. The chance increases to 20 percent Thursday, with a high near 92, and remains at 20 percent Friday, when temperatures should reach about 93. Saturday is forecast to be mostly sunny with a high near 93 and a 10 percent chance of showers and storms.

The broader weather pattern could produce more significant hazards in parts of Arizona, even if Tucson receives little rain. A developing system moving from Texas into New Mexico is expected to draw moisture into the state, with storm chances rising in some areas to as high as 60 percent Thursday and Friday. Forecast discussions warn that storms could bring flash flooding, strong winds, lightning, hail and dust. Those threats will vary by location, and the Tucson forecast remains more modest, but storms in nearby mountain and desert areas can still affect travel and outdoor plans.

Recent storms elsewhere in the state show how quickly conditions can change. Heavy rainfall prompted a flash flood warning for Dudleyville and the Aravaipa Canyon Wilderness, while an outflow moving west across Pinal County was expected to generate dust around Florence, Casa Grande and Maricopa. Additional warnings and advisories were issued in northern Arizona, including near the Dragon Bravo Fire burn scar on the Kaibab Plateau, the Grand Canyon Skywalk area, Grand Canyon Ranch, Meadview and South Cove. Storms were also moving toward Winslow, Flagstaff, Prescott and the Mogollon Rim.

The outlook for Phoenix is different from Tucson’s. A strong ridge of high pressure is expected to expand over the Desert Southwest, bringing Phoenix back toward extreme heat, with lower desert temperatures potentially reaching 110 to 114 degrees Monday and Tuesday. Overnight temperatures there could remain in the upper 80s, with some locations near 90. Although moisture will increase, the high pressure system’s sinking air is expected to suppress most storm development in the Valley, leaving rain chances below 10 percent. The high country north and east of Phoenix could see isolated storms, with chances around 10 to 15 percent.

For Tucson residents, the combination of heat, humidity and isolated storms calls for continued caution even on days when rain is unlikely. Outdoor workers, hikers and people exercising should drink water before, during and after activity, limit strenuous plans during the hottest part of the day and check on friends, relatives and neighbors who may be vulnerable to heat illness. Symptoms of heat exhaustion can include headache, dizziness, weakness, nausea, cool or moist skin and heavy sweating. Confusion, seizures, unconsciousness or a body temperature above 103 degrees can signal heat stroke and require immediate emergency attention.

Rain and thunderstorms also require preparation because dry washes and flooded roadways can become dangerous quickly. Drivers should never enter flowing water, and anyone encountering a flooded road should turn around rather than attempt to cross. Residents are advised to keep flashlights, extra batteries, drinking water, first aid supplies and backup phone power available. During a storm, people should move indoors and stay away from windows, downed power lines and standing water near electrical equipment. Although Tucson’s rain chances remain limited early in the week, the increasing moisture means conditions can shift quickly through the weekend.