SPC AC 280102

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0802 PM CDT Sat Apr 27 2024

   Valid 280100Z - 281200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   NORTH TEXAS...OKLAHOMA...FAR SOUTHEAST KANSAS AND FAR SOUTHWEST
   MISSOURI...

   ...SUMMARY...
   Severe thunderstorms are expected this evening into tonight across
   much of the southern Plains and lower Missouri Valley. The greatest
   severe threat will be from north Texas northeastward through
   Oklahoma into far southeast Kansas and southwest Missouri. All
   hazards will be possible including tornadoes, with some strong,
   damaging wind gusts above 70 mph, and very large hail exceeding 2
   inches in diameter. Scattered severe storms will also be possible
   later this evening in parts of west-central and southwest Texas.
   Isolated severe storms are also expected to occur this evening in
   parts of the mid to upper Mississippi Valley northeastward into the
   Great Lakes.

   ...Southern Plains/Lower Missouri Valley...
   An upper-level trough, evident on water vapor imagery, is
   approaching the southern High Plains. An associated 60 to 80 knot
   mid-level jet streak is currently ejecting northeastward into the
   southern Plains. This feature has been slower than forecast, and
   convective coverage across much of the southern Plains has been slow
   to increase. The lack of convection across much of Oklahoma has
   likely been a result of a capping inversion, that is evident on the
   00Z Norman sounding just below 700 mb. As the mid-level jet streak
   moves over the southern Plains this evening, this cap is expected to
   weaken and the low-level jet will continue to strengthen. This
   should result in a ramp up in convective coverage over the next 2 to
   3 hours, with a line of strong to severe storms developing along the
   western edge of the low-level jet from north Texas through central
   and northeast Oklahoma into southwest Missouri.

   The overall environment from north Texas into Oklahoma and southwest
   Missouri is characterized by moderate instability (MLCAPE around
   2500 J/kg), 0-6 km shear near 60 knots, and 700 to 500 mb lapse
   rates from 8 to 8.5 C/km. This should continue to support the
   development of supercells with large hail this evening. The more
   intense supercells could produce hailstones greater than 2 inches in
   diameter. In addition, the 00Z sounding from Norman has 0-3 km
   storm-relative helicity around 400 m2/s2. This will also be
   favorable for tornadoes. The tornado threat is expected to be
   greatest with either supercells embedded in the line, or with
   discrete cells ahead of the line. Strong tornadoes will be possible.
   As the QLCS organizes this evening, tornadoes may also develop with
   rotating elements within the line itself. This linear MCS is
   expected to produce widespread wind damage and large hail from north
   Texas into central and eastern Oklahoma, and west-central/southwest
   Missouri. The severe threat will likely continue well into the
   overnight period.

   ...Mid to Upper Mississippi Valley/Great Lakes...
   The latest surface analysis shows a front from eastern Iowa
   northeastward into the western Great Lakes. A moist airmass is
   located to the southeast of the front, where surface dewpoints are
   mostly from near 60 into the mid 60s F. The RAP is analyzing MLCAPE
   in the 1000 to 2000 J/kg range, and moderate deep-layer shear across
   much of this airmass near the front. The latest WSR-88D VWP from
   Chicago has 0-6 km shear near 40 knots, and strong speed shear in
   the low-levels. RAP forecast soundings this evening in the vicinity
   also have steep lapse rates. This environment should support
   supercell development with large hail. Wind damage will also be
   possible with supercells and short bowing line segments.

   ..Broyles.. 04/28/2024

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