Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1251 AM CDT Wed Oct 21 2026
Valid 211200Z - 221200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
CENTRAL AND NORTHWESTERN ARIZONA...
...SUMMARY...
Severe thunderstorms with a potential for large hail, severe wind
gusts and a couple tornadoes are expected today along the Mogollon
Rim across parts of Arizona. Marginally severe wind gusts and an
isolated tornado threat will also be possible along the southern and
central California Coast.
...DISCUSSION...
An upper-level low will approach the California Coast today, as
southwesterly divergent flow aloft remains in place over much of the
Southwest. Ahead of the system, low-level moisture will advect
northward into the Desert Southwest today. An axis with surface
dewpoints in the 60s F will set up to the southwest of the Mogollon
Rim across southern, central and western Arizona. By afternoon,
MLCAPE is forecast to peak in the 1500 to 2000 J/kg range along and
near the moist axis. Over the top of the moist and unstable airmass,
strong mid-level southwesterly flow will be in place. Moderate
instability and strong deep-layer shear will support a substantial
severe threat with storms that develop along the Mogollon Rim from
this afternoon into the evening, near the northern edge of the
stronger instability.
As the upper-level system approaches, a 50 to 70 knot mid-level jet
will overspread the Desert Southwest today. RAP forecast soundings
within the exit region of the jet over north-central Arizona in the
mid to late afternoon have gradually veering winds with height and
50 to 60 knots of 0-6 km shear. In addition, steep mid-level lapse
rates and long hodographs are evident which will result in a
potential for supercells with large hail. The strongest cells could
produce hailstones greater than 2 inches in diameter. Forecast
soundings also have 0-3 km storm-relative helicity in the 175 to 250
m2/s2 range late this afternoon along parts of the Mogollon Rim
suggesting that the stronger supercells will be capable of
tornadoes. The severe threat is expected to persist from mid
afternoon into the evening, with a potential for two rounds of
severe storms impacting parts of north-central Arizona.
...Coast of Southern and Central California...
A large upper-level low pressure system will move toward the
California Coast today. The left exit region of a mid-level jet will
approach the southern and central California Coast. A wave of
precipitation associated with this feature will move to the southern
and central California Coast this afternoon. Instability along the
coast will be sufficient for thunderstorm development. RAP forecast
soundings along the coast this afternoon have strong deep-layer
shear, which will support the development of low-topped supercells.
Some model forecasts have 0-3 km storm-relative helicity around 200
m2/s2 near the coast suggesting that an isolated tornado threat will
be possible. Any cells that rotate and move onshore could also be
associated with isolated severe wind gusts as well.
..Broyles/Leitman.. 10/21/2026
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