Weather Update: Rain and thunderstorms set to continue

Phoenix, Arizona: The weather outlook for today through Sunday highlights a moist and unstable monsoon air mass persisting over the region. After localized heavy rainfall on Friday evening, thundershower activity continues this morning across southern Arizona, indicating the unstable monsoon environment.

Key observations show an increase in moisture levels with precipitable water up to 1.68 inches, similar light northeasterly midlevel steering flow, and slight warming in the midlevels, which may reduce instability but could be balanced by the increased moisture. While widespread lower desert storm activity is unlikely, pockets of slow-moving thunderstorms with heavy downpours are expected, particularly from mountain outflow boundaries into the Valley, including Phoenix. Thunderstorm chances peak in the early evening and continue into the overnight hours.

On Sunday, a favorable monsoon setup is expected, with high pressure shifting into the Great Basin, placing Arizona under pronounced northeasterly storm steering flow. Abundant monsoon moisture, especially over the Upper Sonoran Desert, should allow organized storms from the higher terrain northeast of Phoenix to maintain intensity as they move southwestward. Outflow boundary interactions, along with enhanced wind shear and divergent flow aloft, will provide additional lift.

Dangerous heat and humidity persist, with afternoon temperatures expected to reach 110-115°F today and Sunday before any storm activity arrives. Overnight temperatures will remain balmy, ranging from the mid-80s to low 90s.