Scattered severe thunderstorms are expected across the Southwest and Four Corners area today and into tonight, according to a Storm Prediction Center convective outlook. The most intense storms are likely to occur across parts of Arizona and New Mexico, where all severe hazards are possible.
In the Southwest and Four Corners region, a deep upper low moving inland from the California coast is expected to continue eastward and slowly weaken into an open wave. A belt of enhanced southerly mid-level flow along the eastern periphery of the cyclone will remain in place over the area. Several embedded shortwave perturbations are expected to rotate around the cyclone, aiding in continued low-level southerly flow across eastern Arizona and southwest New Mexico. In these areas, surface dewpoints in the upper 50s to low 60s F and diurnal heating could contribute to moderate buoyancy amid deep and strongly veering wind profiles favorable for severe storms.
One or more bands of convection are likely to be ongoing across central and eastern Arizona early this morning. Storms may initially be supercellular, with large hail potentially reaching around 2 inches and a couple of tornadoes being the main concerns, particularly in southeastern Arizona where buoyancy and strong low-level shear overlap. As time progresses, increasing meridional flow and storm interactions may favor linear modes and a transition to a greater damaging wind threat by later in the afternoon.
In the Great Basin, sufficient destabilization for more than sporadic severe storms is less certain due to lower surface dewpoints and significant cloud cover. However, model guidance shows that pockets of better heating from eastern Nevada, Utah, and southwestern Colorado may allow for some development. Damaging wind gusts are noted as the most likely hazard, though marginally severe hail is also possible with stronger rotating storms into the evening.
In Southern California, the upper-level low moving overhead during the afternoon may support weak destabilization. Low-topped convection near the coast may be ongoing early and continue into the early afternoon before mid-level ascent begins to decrease. A brief tornado is possible with the strongest storms, along with isolated wind damage potential. Severe potential should rapidly diminish as the upper trough moves eastward late through the afternoon and into the evening.
The Storm Prediction Center's Day 1 convective outlook includes a slight risk of severe thunderstorms for an area of 45,668 square miles in Arizona, covering population centers including Phoenix, Tucson, Mesa, Glendale, and Chandler. A marginal risk is identified for 199,809 square miles in California, including Los Angeles, Long Beach, Santa Ana, Anaheim, and Riverside. In Utah, a 5% risk of hail is noted for an area of 189,353 square miles, covering Salt Lake City, West Valley City, Provo, West Jordan, and Orem.
