Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0250 PM CDT Thu Sep 18 2025
Valid 182000Z - 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.
...20z Update...
The previous forecast remains on track. The primary adjustment was
an eastward expansion of 5% wind/hail probabilities into northwest
AR where pulse convection is developing within a very buoyant
(though weakly sheared) environment. Similar thermodynamic/kinematic
conditions have yielded sporadic wind/hail reports in recent days,
so at least a low-end severe threat is anticipated through early
evening (see MCD #2096 for additional details).
Elsewhere, the forecast remains on track. Convection is beginning to
deepen across northeast OK, far eastern KS, and far southwest MO,
which is expected to increase in coverage and intensity within the
Slight risk area through the evening based on recent environmental
data and CAM solutions. Further west, consideration was given for
removing risk probabilities across eastern TX into western OK;
however, surface convergence along a diffuse front is gradually
increasing with an attendant uptick in mid-level cumulus. Forecast
soundings and a couple of recent HRRR/RRFS solutions hint that
elevated convection along the boundary remains possible through
mid-evening, and deep-layer wind shear is sufficient for organized
convection. Across central OK, elevated thunderstorms developing
late tonight within a modest warm advection regime may pose a threat
for isolated large hail. See the previous discussion below and MCDs
#2097 and #2098 for additional details.
..Moore.. 09/18/2025
.PREV DISCUSSION... /ISSUED 1139 AM CDT Thu Sep 18 2025/
...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.
Read more CHECK UPDATE ZOOM GRAPHIC
http://dlvr.it/TN8zCY
