Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1139 AM CDT Thu Sep 18 2025
Valid 181630Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
MISSOURI...
...SUMMARY...
Isolated severe storms are possible mainly from late afternoon into
tonight across Missouri into adjacent parts of the Lower Missouri
Valley and southern Plains. Isolated strong to severe storms may
also occur across southern California and the Lower Colorado River
Valley.
...Missouri and Lower Missouri Valley to southern Plains...
Generally isolated severe storms will be possible today regionally
ahead of the east/southeast-advancing front (and residual
convection/outflows), but a somewhat greater/semi-focused corridor
of severe potential, mostly in the form of damaging winds, appears
to exist across portions of Missouri. This will be influenced by
modestly stronger cyclonic flow aloft attendant to the
mid/upper-level trough, with a favorably warm/moderately unstable
boundary layer this afternoon. Bouts of damaging winds will be
possible regionally, with some hail as well.
...Southern California/Lower Colorado River Valley....
An anomalously moist airmass associated with the remnants of
tropical cyclone Mario continues to advect northward into and across
southern portions of California/Arizona. 12Z NKX sounding sampled a
1.95 PW value, which is well above the 90th percentile based on
daily SPC sounding climatology. Filtered heating is anticipated
within this moist environment, resulting in moderate buoyancy across
much of eastern southern California and southwest Arizona this
afternoon. Moderate vertical shear is anticipated as well,
particularly across southern California. Additional thunderstorm
development is expected during the afternoon, with a predominantly
multicellular mode. However, enough shear and instability are in
place to support organization with any more persistent updrafts, and
a few supercells capable of damaging gusts are possible. A
very-low-probability tornado threat may exist as well, particularly
in the Lower Colorado Valley vicinity where some guidance suggests
surface winds stay more southeasterly. Even so, the low-level flow
is weak and any tornado threat should be very localized.
...Eastern South Dakota/southeast North Dakota/western Minnesota...
In proximity to the upper low over the Dakotas, a relatively moist
environment, sufficient cloud breaks/heating, ample low-level CAPE,
and ambient vorticity near a weak surface low and nearby front could
be sufficient for some funnels this afternoon through around sunset.
A brief non-supercell tornado cannot be conclusively ruled out near
the boundary/surface low if stronger destabilization materializes,
but the overall potential/likelihood should remain limited.
..Guyer/Thornton.. 09/18/2025
Read more CHECK UPDATE ZOOM GRAPHIC
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