A Rare and Significant Severe Weather Threat in the Southwest
Good evening, folks! Today, we're going to be taking a look at a rather unusual severe weather setup developing across the southwestern United States.
Whenever we think of severe weather, we typically think of the Great Plains or the Southeast. However, Wednesday is shaping up to bring the threat of severe thunderstorms to the desert Southwest.
The Southwest is typically known for its hot, dry climate, and when we think about severe weather across the U.S., this region is generally much lower on the list of places most likely to experience it.
However, an interesting setup will be unfolding tomorrow, Wednesday, with severe thunderstorms expected across Arizona and surrounding portions of the Four Corners region. In fact, some areas could experience a particularly significant severe weather threat, with the potential for large hail, damaging winds, and even tornadoes.
The primary driver behind this setup is a deep upper-level trough approaching the California coast. As this system moves inland, it will bring a substantial increase in wind speeds throughout the atmosphere, while relatively rich moisture across the region helps provide the instability needed for thunderstorms to develop. This combination is especially concerning for Arizona, where the environment could support organized supercells capable of producing multiple rounds of severe weather throughout the afternoon and evening.
Arizona is expected to see the most significant severe weather threat, with an Enhanced Risk in place across portions of the state, particularly toward central Arizona. What makes this setup particularly notable is the potential for a combination of severe weather hazards that are relatively uncommon for the region.
Forecast guidance indicates that instability could reach around 500–1,000 J/kg of mixed-layer CAPE. While these values may not seem especially impressive compared to some of the major severe weather setups seen across the Great Plains, they become much more concerning when combined with the strong wind shear expected throughout the atmosphere. This is shaping up to be a classic high-shear, low-CAPE environment, which could support sustained supercells despite the relatively modest instability. These storms could produce large to very large hail, with some hailstones potentially exceeding two inches in diameter.
However, hail is not the only concern. Wind profiles across parts of Arizona may also support tornado development, particularly across central and northern portions of the state. Farther north, relatively lower temperature-dewpoint spreads and a more southeasterly component to surface winds could contribute to increased low-level wind shear and atmospheric rotation. This would create a more favorable environment for tornadoes, particularly where storms remain discrete and develop persistent rotation.
The threat may also extend beyond Arizona into southeastern Nevada and far southern Utah, depending on how storms develop and evolve throughout the day.
Another factor worth watching is the duration of this event. While the greatest severe weather threat is expected during the afternoon and evening hours, storms across central and northern Arizona could continue well into Wednesday night and potentially persist into early Thursday morning. This means some areas may experience multiple rounds of severe thunderstorms rather than a single, brief period of activity.
Farther west, portions of the central and southern California coast could also experience isolated severe thunderstorms as the upper-level system approaches. An exceptionally strong jet stream, with winds reaching around 80 knots at the 500-millibar level, is expected to move across the region during the latter part of the forecast period.
Moisture moving inland from the Pacific will interact with colder air aloft, creating enough instability to support scattered thunderstorms. However, instability along the coast is expected to remain relatively limited, meaning these storms will likely be less intense than those anticipated across Arizona.
The primary concern along the California coast will be localized damaging wind gusts from stronger thunderstorms. Brief, isolated tornadoes or waterspouts cannot be ruled out either, particularly near the coastline.
Thursday: The Severe Weather Threat Continues
Now, while Wednesday will likely be the main event, the severe weather threat isn't going to end there. As we head into Thursday, the upper-level trough responsible for this setup will continue moving inland, shifting northeastward toward the Lower Colorado River Valley. Although the wind shear is expected to weaken somewhat as the system progresses, conditions should remain favorable for additional organized thunderstorms across parts of the Southwest and Four Corners region.
The greatest concern on Thursday will once again be across central and eastern Arizona, where the combination of wind shear and instability could support isolated severe thunderstorms. While the overall environment may not be quite as favorable as it is on Wednesday, there will still be enough support for organized storm development, including supercells and sustained multicell thunderstorms. These storms could produce large hail and damaging wind gusts, with a tornado or two also possible.
One factor that could influence Thursday's threat is the potential for lingering cloud cover and precipitation from earlier storms. This could limit daytime heating and reduce instability across portions of the region, potentially keeping the overall severe weather threat somewhat more limited. However, even with somewhat weaker instability, the wind profiles are expected to remain supportive of organized thunderstorms, meaning severe weather cannot be ruled out.
A Powerful Nor'easter Off the East Coast
Now, shifting our attention away from the Southwest and toward the Atlantic, we have another developing weather system worth keeping an eye on. A strong nor'easter is currently churning a few hundred miles off the coast of North Carolina, producing storm-force winds offshore along with showers and thunderstorms, primarily to the west of its center.
Currently, the system retains its frontal features, meaning it is still behaving like a typical mid-latitude storm rather than a tropical or subtropical cyclone. However, over the next couple of days, this could begin to change. As the nor'easter moves slowly north-northeastward over the Gulf Stream, it may gradually lose some of its frontal characteristics while thunderstorms begin developing closer to the center of circulation. If this convection becomes sufficiently organized, the system could briefly acquire subtropical characteristics.
The Gulf Stream will be an important factor to watch here. Its relatively warm waters could help support thunderstorm development near the low-pressure center, potentially allowing the system to become less dependent on the temperature contrasts associated with its existing frontal structure. However, this transition is far from guaranteed, and for now, the system remains a powerful non-tropical storm.
By the end of the week, the nor'easter is expected to accelerate northeastward and move farther away from the eastern United States. As it does so, environmental conditions are forecast to become increasingly unfavorable for additional subtropical or tropical development. This should limit the system's opportunity to undergo any further transition, even if it briefly acquires some subtropical characteristics beforehand.
While the potential for subtropical development is certainly interesting, the more immediate concern is the impact this storm could have along the East Coast. Regardless of whether the system ever develops subtropical characteristics, high winds, coastal flooding, and dangerous surf are expected along portions of the coastline over the next several days.
The strong wind field surrounding the nor'easter could produce hazardous conditions along exposed coastal areas, while persistent onshore winds in some locations may contribute to coastal flooding. The storm has caused the closure of the newly repaired NC-12 after it was recently damaged by another nor'easter. Meanwhile, dangerous surf and rough seas could create hazardous conditions for beachgoers, boaters, and anyone venturing onto the water.
And with that, I'll wrap up today's forecast, folks! As always thank y'all for reading, and I'll see you in the next forecast!