SPC AC 210717
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0217 AM CDT Thu Oct 21 2021
Valid 231200Z - 241200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER A PORTION
OF THE CENTRAL PLAINS...
Storms may pose a risk for mainly isolated large hail Saturday
evening/night, primarily across a portion of the central Plains.
...Central Plains region...
Models are trending toward better agreement and have demonstrated
some run-to-run consistency regarding the evolution of a
southern-stream shortwave trough forecast to amplify as it
approaches the southern and central High Plains late Saturday night.
However, some model differences still persist especially regarding
the amplitude of this feature. Preceding this impulse, a
strengthening southerly low-level jet east of an evolving lee
surface low will foster the advection of partially modified Gulf air
northward through the southern and central Plains. By Saturday
evening this low will be situated across western KS with a dryline
southward through western TX. A warm front will extend east from the
low through central or northern KS and into southwest MO.
Destabilization associated with low-level theta-e advection beneath
plume of steeper mid-level lapse rates will result in moderate
instability across KS overnight. Increasing isentropic ascent north
of the warm front promoted by the low-level jet should contribute to
development of elevated storms across northern KS and adjacent areas
of southeast NE, northwest MO and southwest IA. Steep mid-level
lapse rates, moderate instability and sufficient effective bulk
shear for mid-level updraft rotation will contribute to a threat for
large hail overnight, especially before storms consolidate into an
A conditional, somewhat greater severe threat exists for the
possibility of surface-based storm initiation along the warm front
across central/northern KS. At this time the probability of this
scenario appears low, but will be re-evaluated in day 2 updates.
A conditional risk for a couple of strong to severe storms will
exist from western OK into northwest TX Saturday during the late
afternoon and early evening. However, relatively weak convergence
along the dryline and limited deeper forcing, along with the
likelihood of a capping inversion suggest it should be difficult to
initiate surface-based storms.
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