Monsoon becomes much more active this weekend and a Flash Flood Watch will be in effect through Sunday night

Tucson residents should prepare for a much wetter and stormier weekend, with a Flood Watch covering the metro area from Saturday morning through late Sunday night. Increased moisture and atmospheric instability are expected to fuel scattered thunderstorms across southern Arizona. Some storms could drop more than an inch of rain in a short period, creating localized flooding in washes, low lying areas, streets and neighborhoods that collect runoff.

The weather pattern is expected to become active across southeast Arizona as deep moisture remains over the region and conditions shift higher in the atmosphere. Storm coverage could range from scattered to numerous, with many storms producing roughly one half inch to one inch of rain. The strongest cells could bring locally heavier totals between one and three inches. Because storms may repeatedly pass over some locations, the risk is not limited to a single downpour.

The increased cloud cover and rain chances should also provide some relief from the recent heat. Forecast information calls for Tucson area highs to fall back into the upper 90s by Sunday, following an extreme heat period that continued into Friday. Elsewhere in Arizona, temperatures also are expected to cool as monsoon moisture spreads across the state. The Phoenix area, for example, had reached 112 degrees during the week, while a record warm morning low of 94 degrees was recorded there.

The storm threat extends well beyond Tucson. Forecasts call for thunderstorms across central, northern and southern Arizona, with heavy rain and potentially severe wind gusts. Storms already developed in parts of southern Arizona, including areas south and southeast of the Phoenix region, where outflow boundaries were expected to move north and northwest toward the Valley and Pinal County. Those boundaries can bring sudden wind shifts, dust and new storm development.

Blowing dust is another concern for people traveling across southern Arizona. A dust advisory covered much of the region, with possible wind gusts from 45 to 55 mph and visibility falling below one mile in some areas. Storms may arrive behind the dust and outflow winds, bringing damaging gusts as well as heavy rain. The broader weather pattern was expected to continue overnight into Monday morning, with widespread rainfall moving northeast across central and northern Arizona. Flood Watches in portions of central and northern Arizona were reported to continue through Monday evening, while the watch for the Tucson area and southern Arizona was set through late Sunday night.

Local forecast details point to the possibility of storms continuing after the weekend as well. One forecast called for a 20 percent chance of showers and thunderstorms after 2 p.m., increasing clouds and a high near 96 degrees, followed by a 50 percent overnight chance, mainly after 2 a.m. The following day was expected to remain mostly cloudy, with a high near 93 and a 60 percent chance of precipitation. Additional storm chances of 60 percent were listed for the next day, before conditions were expected to turn drier and warmer, with highs returning to the mid and upper 90s and eventually reaching the low 100s.

For Tucsonans, the principal danger is not simply the amount of rain but how quickly water can collect and move. The American Red Cross advises drivers never to enter a flooded roadway. Anyone who encounters rising water should turn around and find another route. If water begins rising around a vehicle, the driver and passengers should leave quickly and move to higher ground, if it is safe to do so. People in flood prone neighborhoods should be ready to evacuate and should wait for officials to say an area is safe before returning.

Residents should also keep away from downed power lines and avoid puddles or standing water near electrical hazards. During an outage, officials recommend using a flashlight rather than an open flame. Households can prepare by keeping extra batteries, a first aid kit, drinking water and food that does not require cooking or refrigeration. People who depend on powered medical equipment should have backup power, and cell phones should be charged or supported by an alternate power source.

Thunderstorms can also interrupt water, power and gas service, while strong winds and dust can make travel hazardous with little warning. The Red Cross recommends creating and practicing a household storm plan, keeping a battery powered or hand crank radio available, and selecting an interior place away from windows, skylights and glass doors. Tucson residents should monitor updated weather information throughout the weekend, avoid unnecessary travel during the strongest storms, and remember that even a short distance of moving water can sweep away a vehicle.