Severe Weather Risk and Atmospheric Conditions in Arizona and Southern California

Meteorological Overview

On Wednesday, parts of Arizona and Southern California will experience a rare severe-weather risk. The National Weather Service Storm Prediction Center has identified a marginal risk, which is Level 1 out of 5, in areas including Phoenix and Tucson.

Tornado Potential

An isolated and brief tornado might occur along Southern California’s immediate coastline. This risk arises because rotating cells could bring waterspouts to the coast. If a waterspout reaches the shore, it would briefly cause tornado-like damage before dissipating within a short distance inland.

Weather System Dynamics

The weather system responsible for this risk involves an upper-level low. This is a high-altitude region characterized by cold air, low pressure, and spin. On Tuesday afternoon, this system was located offshore from Southern California, propelling warm and moist air northward.

Flood Watch in Arizona

The same meteorological setup will cause an influx of Pacific moisture into Arizona. This has led to a flood watch for the majority of the state.

Expectations for Showers and Thunderstorms

The enriched air mass will likely result in showers and storms, with the possibility of severe thunderstorms in the afternoon. These storms can quickly deliver one to two inches of rainfall, which could lead to localized flash flooding due to Arizona’s sandy soils.

Risk of Supercells

Some storms might evolve into supercells, which are rotating thunderstorms. The upper-level low-pressure area is inducing a kink in the jet stream, forming a trough. This introduces wind shear, impacting tall thunderstorm clouds and causing them to rotate, thereby increasing tornado risk. While tornadoes are uncommon in this region, current conditions elevate this possibility.