SPC Oct 22, 2026 0600 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0100 AM CDT Thu Oct 22 2026

Valid 221200Z - 231200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL AND
EASTERN ARIZONA INTO WESTERN NEW MEXICO...

...SUMMARY...
Scattered severe thunderstorms are expected across the Southwest and
Four Corners area today into tonight with the most intense storms
likely across parts of Arizona and New Mexico. All severe hazards
will be possible.

...Southwest and Four Corners...
The deep upper low initially over the CA coast will move inland and
continue eastward through the day, slowly weakening into an open
wave. A belt of enhanced southerly mid-level flow (70+ kt) along the
eastern periphery of the cyclone will remain in place over the
Southwest and Four Corners. Several embedded shortwave perturbations
will rotate around the cyclone, aiding in continued low-level
southerly flow across eastern AZ and southwest NM. Here, surface
dewpoints in the upper 50s to low 60s F and diurnal heating should
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/eastern AZ early this morning along a weak surface trough.
Cooling mid-level temperatures ahead of the approaching low and
persistent upslope flow along the central and southern portions of
the Mogollon Rim will maintain buoyancy through the diurnal minimum
with reintensification of these storms likely as heating develops
over the lower deserts. Storms will likely be supercellular
initially. Large hail (perhaps to around 2 inches) and a couple of
tornadoes will be the main concern, focused where the largest
buoyancy and strongest low-level shear will overlap in southeastern
AZ. With time, increasingly meridional flow and numerous storm
interactions will favor more linear modes and perhaps a transition
to a greater damaging wind threat by later in the afternoon.

Farther north into the Great Basin, sufficient destabilization for
more than sporadic severe storms is much less certain owing to lower
surface dewpoints and significant cloud cover. Still, model guidance
shows a few hundred J/kg of MLCAPE may develop with pockets of
better heating from eastern NV, UT and into southwestern CO. Flow
aloft will remain fairly strong (50-60 kt) helping to elongate mid
and upper-level hodographs. DPVA and upslope trajectories should
support numerous showers/thunderstorms with some potential for
organization into clusters or supercell structures. Damaging wind
gusts are the most likely hazard, though marginally severe hail is
also possible with any of the stronger rotating storms into the
evening.

...Southern California...
As the upper-level low moves overhead during the afternoon, cold
mid-level temperatures (around -20C at 500 mb) and modest surface
heating will support weak destabilization with MLCAPE of 500-750
J/kg. Low-topped convection near the coast may be ongoing early and
continue 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. Severe potential
should rapidly diminish as the upper trough moves eastward late
through the afternoon and into the evening.

..Lyons/Jirak.. 10/22/2026


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SPC Oct 21, 2026 2000 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 2000Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0253 PM CDT Wed Oct 21 2026

Valid 212000Z - 221200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
CENTRAL ARIZONA...

...SUMMARY...
Severe thunderstorms capable of producing large hail, a few
tornadoes, and damaging winds remain possible today and tonight
across parts of Arizona and vicinity. Isolated severe gusts and
perhaps a tornado may also occur along the central/southern
California Coast.

...20z Update...
No changes were made to the existing outlook with this update as the
forecast remains generally on track. Convective activity/severe
potential is generally expected to peak this afternoon/early evening
coincident with peak diurnal heating/destabilization. However,
additional rounds of thunderstorm development and the potential for
supercells capable of primarily large hail are likely to continue
into the late evening/overnight hours, especially across
central/northern Arizona, amid a continuing southerly, warm-air
advection regime. See MCDs #2387 and #2388 along with the discussion
below for additional short-term details.

..Chalmers.. 10/21/2026

.PREV DISCUSSION... /ISSUED 1122 AM CDT Wed Oct 21 2026/

...Southwest...
Recent satellite imagery continues to show deep southwesterly flow
aloft from the central Baja Peninsula through AZ and the Four
Corners region. Warm-air advection associated with this
southwesterly flow aloft has contributed to showers and
thunderstorms across central/northern AZ this morning. The low-level
airmass here is still relatively cool and stable, but strong
vertical shear has still resulted in several supercells. As
mentioned in MCD #2385, additional/isolated thunderstorms are
possible within this low-midlevel moisture plume, potentially aided
by embedded speed maxima moving north-northeastward. Strong vertical
shear will persist as well, suggesting several of these storms could
become supercellular. Large hail will remain the primary risk until
the low levels destabilize.

Deep cyclone off the central/southern CA coast is forecast to
gradually shift east-southeastward today. As it does, southwesterly
flow aloft within its eastern periphery will strengthen, with
deep-layer vertical shear across AZ also strengthening in response.
Low-level moisture will advect northward as well. Even with
widespread cloudiness, this increased moisture combined with
filtered daytime heating will support gradual airmass
destabilization and the development of up to 1000-1500 J/kg of
MLCAPE across this region. Strongest buoyancy is anticipated in
south-central AZ.

Forcing for ascent will increase in tandem with airmass
destabilization and the general expectation is for increasing
thunderstorm coverage along and just south/west of the Mogollon Rim
this afternoon. Supercell wind profiles are in place, and large to
isolated very large hail (i.e. 2"+ in diameter) is expected to be
the primary hazard. However, storm motion will take these storms
north-northeastward, potentially interacting with the more
southeasterly low-level flow along/near the Rim. Resulting increase
in low-level shear will support an increased tornado potential. This
potential will be maximized from northwest into central AZ this
afternoon and early evening, but low-probability tornado potential
will extend to the southern AZ/NM border. Strong wind gusts are
possible as well, particularly from central into southeast AZ where
relatively stronger heating/mixing is possible.

Tornado threat is expected to diminish gradually with the loss of
daytime heating, but thunderstorms will likely persist throughout
the evening and overnight. Large hail will remain possible with this
overnight activity.

...Coastal Central/Southern California...
The large cyclone over the eastern Pacific will approach the
central CA Coast through the period, with a belt of strong southerly
flow at mid levels expected to overspread coastal central/southern
CA through the day. A low-topped line of convection may develop in
response and impact this region during the afternoon/evening.
Limited instability is forecast, and updrafts may struggle to reach
sufficient depth for charge separation and lightning production.
Even so, given modestly enhanced flow and low-level shear, an
isolated risk for severe gusts and perhaps a tornado may exist as
this convection moves onshore.


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SPC Oct 21, 2026 1630 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1630Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1122 AM CDT Wed Oct 21 2026

Valid 211630Z - 221200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
CENTRAL ARIZONA...

...SUMMARY...
Severe thunderstorms capable of producing large hail, a few
tornadoes, and damaging winds are expected today and tonight across
parts of Arizona and vicinity. Isolated severe gusts and perhaps a
tornado may also occur along the central/southern California Coast.

...Southwest...
Recent satellite imagery continues to show deep southwesterly flow
aloft from the central Baja Peninsula through AZ and the Four
Corners region. Warm-air advection associated with this
southwesterly flow aloft has contributed to showers and
thunderstorms across central/northern AZ this morning. The low-level
airmass here is still relatively cool and stable, but strong
vertical shear has still resulted in several supercells. As
mentioned in MCD #2385, additional/isolated thunderstorms are
possible within this low-midlevel moisture plume, potentially aided
by embedded speed maxima moving north-northeastward. Strong vertical
shear will persist as well, suggesting several of these storms could
become supercellular. Large hail will remain the primary risk until
the low levels destabilize.

Deep cyclone off the central/southern CA coast is forecast to
gradually shift east-southeastward today. As it does, southwesterly
flow aloft within its eastern periphery will strengthen, with
deep-layer vertical shear across AZ also strengthening in response.
Low-level moisture will advect northward as well. Even with
widespread cloudiness, this increased moisture combined with
filtered daytime heating will support gradual airmass
destabilization and the development of up to 1000-1500 J/kg of
MLCAPE across this region. Strongest buoyancy is anticipated in
south-central AZ.

Forcing for ascent will increase in tandem with airmass
destabilization and the general expectation is for increasing
thunderstorm coverage along and just south/west of the Mogollon Rim
this afternoon. Supercell wind profiles are in place, and large to
isolated very large hail (i.e. 2"+ in diameter) is expected to be
the primary hazard. However, storm motion will take these storms
north-northeastward, potentially interacting with the more
southeasterly low-level flow along/near the Rim. Resulting increase
in low-level shear will support an increased tornado potential. This
potential will be maximized from northwest into central AZ this
afternoon and early evening, but low-probability tornado potential
will extend to the southern AZ/NM border. Strong wind gusts are
possible as well, particularly from central into southeast AZ where
relatively stronger heating/mixing is possible.

Tornado threat is expected to diminish gradually with the loss of
daytime heating, but thunderstorms will likely persist throughout
the evening and overnight. Large hail will remain possible with this
overnight activity.

...Coastal Central/Southern California...
The large cyclone over the eastern Pacific will approach the
central CA Coast through the period, with a belt of strong southerly
flow at mid levels expected to overspread coastal central/southern
CA through the day. A low-topped line of convection may develop in
response and impact this region during the afternoon/evening.
Limited instability is forecast, and updrafts may struggle to reach
sufficient depth for charge separation and lightning production.
Even so, given modestly enhanced flow and low-level shear, an
isolated risk for severe gusts and perhaps a tornado may exist as
this convection moves onshore.

..Mosier/Thompson.. 10/21/2026


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SPC Oct 21, 2026 1300 UTC Day 1 Convective Outlook

LIVE MAP (ABOVE) ... SPC 1300Z Day 1 Outlook


Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0730 AM CDT Wed Oct 21 2026

Valid 211300Z - 221200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
ARIZONA...

...SUMMARY...
Severe thunderstorms capable of producing large hail, a few
tornadoes, and damaging winds are expected today and tonight across
parts of Arizona and vicinity. Isolated severe gusts and perhaps a
tornado may also occur along the central/southern California Coast.

...Southwest...
Ongoing thunderstorms across central/northern AZ early this morning
are being aided by large-scale ascent associated with a strong
southwesterly mid/upper-level jet. This activity should continue to
pose a threat for mainly isolated severe hail in the short term,
with 40-50 kt of effective bulk shear aiding updraft organization
and supercell potential in an otherwise weakly unstable environment
(MUCAPE generally 500-1000 J/kg at the moment). Current expectations
are for these thunderstorms to continue advancing northward into an
even less unstable environment, but regenerative convection may
persist for much of the morning as additional cells move over the
Mogollon Rim.

In the wake of this morning convection, an already unseasonably
moist low-level airmass present across southern/central AZ is
forecast to slowly spread northward across the lower CO River Valley
and Mogollon Rim vicinity through the afternoon. Even with
widespread cloudiness, filtered daytime heating will support gradual
airmass destabilization and the development of up to 1000-1500 J/kg
of MLCAPE across this region (locally stronger in central AZ), as
convective inhibition becomes minimal by 18-20Z. Additional
thunderstorms will likely develop across central/northern AZ in this
time frame, as persistent forcing for ascent attendant to the
mid/upper-level southwesterly jet remains over the Southwest.

Strong deep-layer shear (40-55+ kt) will easily support supercells,
with an associated threat for large hail. Greater instability is
forecast with southward/westward extent in central AZ and southern
NV, but lower thunderstorm coverage may exist in these areas. Still,
a conditional risk for 2+ inch diameter hail remains apparent with
splitting supercells given the rather favorable overlap of moderate
instability and elongated/nearly straight hodographs at mid/upper
levels. Occasional severe/damaging winds may also occur, but the
tendency for convection to remain mostly discrete may limit
clustering potential to some extent.

The tornado threat with these supercells remains somewhat uncertain,
as temperatures will remain fairly cool across northern AZ today.
Even so, the risk for a few tornadoes may focus across parts of
northwest/north-central AZ this afternoon and early evening, where
greater low-level shear is forecast to reside amid generally
east-southeasterly low-level winds. It should also be noted that
multiple rounds of strong to severe thunderstorms appear likely
today into tonight. Primary changes with this update were to extend
the Slight Risk westward across northwest AZ/southeast NV/southwest
UT mainly for large hail potential with supercells this
afternoon/evening, and to expand the Marginal Risk in southern NV
and western NM.

...Coastal Central/Southern California...
A large, closed upper low over the eastern Pacific will approach the
central CA Coast through the period, with a belt of strong southerly
flow at mid levels expected to overspread coastal central/southern
CA through the day. A low-topped line of convection may develop in
response and impact this region during the afternoon/evening.
Instability is forecast to remain minimal/shallow, and this activity
may struggle to reach sufficient height for charge separation and
lightning production. Still, given modestly enhanced flow and
low-level shear, an isolated risk for severe gusts and perhaps a
tornado may exist as this convection moves onshore.

..Gleason/Kerr.. 10/21/2026


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