Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1229 PM CDT Wed Oct 21 2026

Valid 221200Z - 231200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PORTIONS OF
SOUTHEAST ARIZONA...

...SUMMARY...
Scattered severe thunderstorms are expected across the Southwest and
Four Corners area on Thursday, with the greatest risk across parts
of Arizona. All severe hazards will be possible.

...Synopsis...
An broad upper trough with an embedded upper low off the southern
California coast will move eastward on Thursday. This feature will
become more of an open wave with a modest negative tilt with time.
Above normal low-level moisture will be in place within the
Southwest. Widely scattered to scattered storms are expected, some
of which may be strong to severe.

...Southwest into parts of the Great Basin...
Strong meridional flow associated with the approaching upper-trough
will overspread parts of the Great Basin and Southwest through the
day. Moisture/destabilization will be more limited with
northward/eastward extent. Some convection will be possible early in
the period across much of the region. Depending on where pockets of
greater heating can occur, widely scattered to scattered storms are
expected to develop during the afternoon both within the terrain and
along a surface trough within the central Great Basin. Isolated
marginally severe hail and severe winds will be the primary
concerns. The potential for a tornado will increase within southern
Utah into Arizona where surface flow will be more backed greater
destabilization is more probable.

With the upper-trough becoming more of an open wave with time, the
most favorable overlap of mid-level ascent, surface heating, and
steeper mid-level lapse rates will be across parts of southeast
Arizona. Storms will likely be supercellular initially. Large hail
(perhaps to around 2 inches) and a couple of tornadoes will be the
main concern. With time, storm interactions and an increasing linear
mode will mean a transition to more a wind threat by later in the
afternoon. Destabilization from the Mogollon Rim northward becomes
more uncertain given the signal for early clouds/precipitation.

...Coastal Southern California...
As the upper-level low moves overhead during the afternoon,
temperatures aloft will become quite cold (around -20C at 500 mb).
Modest surface heating will lead to around 500-750 J/kg MLCAPE,
potentially. Low-topped convection near the coast is possible during
the morning into the early afternoon before mid-level ascent begins
to decrease. Given the ambient vorticity with the upper-low and
local terrain effects, a brief tornado is possible with the
strongest storms along with isolated wind damage potential.

..Wendt.. 10/21/2026