SPC AC 191639

   Day 1 Convective Outlook CORR 1
   NWS Storm Prediction Center Norman OK
   1139 AM CDT Wed Apr 19 2023

   Valid 191630Z - 201200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS MID-MO
   VALLEY...

   CORRECTED FOR HAIL AND CATEGORICAL LINES IN IL

   ...SUMMARY...
   Multiple rounds of scattered severe thunderstorms are expected from
   late afternoon into tonight across the Mid-Missouri Valley. Very
   large hail is likely, and significant severe wind gusts along with a
   few tornadoes will be possible. A conditional threat for isolated
   significant severe storms also exists farther south into
   western/central Oklahoma and western north Texas this evening.

   ...Mid-MO Valley...
   Three rounds of severe potential appear increasingly evident across
   the Mid-MO Valley vicinity beginning in the late afternoon and
   continuing tonight. The first should consist of elevated
   thunderstorms north of the slow-moving/quasi-stationary warm front
   that is arcing east of the initial primary surface cyclone over
   southeast NE. This activity near the NE/SD/IA border will probably
   evolve into a couple of elevated supercells within an
   eastward-moving cluster, owing to favorable cloud-bearing shear
   along the northern gradient of the peak buoyancy plume across the
   central Great Plains. Large hail will be the primary hazard. 

   A separate area of dryline to warm-sector storm development is
   anticipated towards the KS/NE/MO/IA border during the early evening
   in the exit region of a strengthening low-level jet in OK/KS/MO.
   This ascent combined with the boundary-layer thermal ridge from
   western OK to central/eastern KS should be enough to overcome the
   pronounced elevated mixed-layer across the Great Plains. 12Z NAM
   guidance remains terribly inconsistent with the 00Z ECMWF, recent
   RAP guidance, and comparison to surface observations. It is already
   much too cool with current temperatures with it's typical too
   cool/moist boundary layer. It appears more likely that a relatively
   well-mixed boundary layer within this portion of the warm/moist
   sector will be characterized by surface dew points from 58-61 F as
   storms form. This will seemingly support a mix of large hail,
   damaging wind gusts, and a couple tornadoes with supercells that
   initially form. Given a relatively confined buoyancy plume,
   regenerative convection is likely through the evening, yielding a
   broadening cluster with embedded supercell structures. 

   Tonight, a third round of severe storms should develop near the
   south-central NE/north-central KS border. This should occur as a lee
   cyclone over the central High Plains shifts east, in association
   with a shortwave impulse progressing through the basal portion of
   the broader mid-level trough over the West. A surge of low-level
   moisture northwestward amid an intense 60-70 kt low-level jet should
   support emerging elevated supercell clusters that track east
   overnight, potentially merging with lingering convection downstream.
   Severe wind gusts and large hail will be the primary threats. 

   ...Western/central OK into western north TX...
   Storm development is uncertain along the dryline during the late
   afternoon to early evening, given little in the way of height
   falls/forcing for ascent, and the presence of a substantial
   warm-sector cap. Storm initiation will rely on the depth of mixing
   with surface heating along the dryline, and on parcel residence time
   in the dryline zone of ascent. Flow in the 850-700 mb layer will be
   a bit more parallel to the dryline compared to yesterday, which may
   allow long enough residence times to reach an LFC. If storms form,
   the environment favors a threat of isolated very large hail with any
   sustained supercell.

   During the evening, substantial intensification of the low-level jet
   and an increase in boundary-layer moisture renders concern for a
   conditional strong tornado threat after dusk. Overall moisture
   appears a bit less compared to past nocturnal intense tornado events
   and confidence is low in whether a supercell or two can become
   established prior to increasing MLCIN during the late evening. As
   such, confidence in occurrence/coverage is low, but intensity is
   conditionally significant.

   ..Grams/Thornton.. 04/19/2023

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