SPC AC 270604

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0104 AM CDT Sat Apr 27 2024

   Valid 271200Z - 281200Z

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

   ...SUMMARY...
   Numerous severe thunderstorms are likely today and tonight across
   the southern and central Plains into the lower to mid Missouri
   Valley. The greatest potential for severe storms will be from north
   Texas into Oklahoma and southeast Kansas, where strong tornadoes,
   very large hail over 2 inches in diameter and widespread damaging
   winds (some over 70 mph), are expected to occur. A broader area of
   severe threat will extend from south-central Texas
   north-northeastward to the Great Lakes.

   ...Tornado Outbreak Expected Today From North Texas into
   Oklahoma...Southeast Kansas and Far Southwest Missouri...

   ...Southern Plains...
   An upper-level trough will move through the Desert Southwest today
   as an 80 to 90 knot mid-level jet translates quickly eastward
   through the base of the system. Ahead of the trough, a moist and
   unstable airmass will be in place across much of the southern and
   central Plains. At the surface, a low will move eastward across
   southwest Kansas with a dryline extending southward through far
   western Oklahoma and west Texas. Surface dewpoints to the east of
   the dryline will be in the mid to upper 60s F. In response to warm
   advection this morning, a cluster of thunderstorms is expected to
   develop to the east of the dryline across northwest Texas. This
   cluster is forecast to spread north-northeastward into western
   Oklahoma by late morning. Large hail and wind damage will be likely
   with the stronger cells within this cluster. An outflow boundary
   with this convection should setup across west-central Oklahoma by
   early afternoon, with a moist and unstable airmass extending
   eastward from the boundary across much of central and eastern
   Oklahoma northward into southeast Kansas. This undisturbed airmass
   is expected to be favored for the greatest severe threat this
   afternoon and evening.

   The mid-level jet is forecast to eject quickly northeastward across
   the southern Plains this afternoon. This will result in strong
   deep-layer shear across most of the southern Plains, and will create
   a large-scale mass response that will be very favorable for severe
   storms, including supercells and bowing line segments. As the core
   of the mid-level jet moves into the southern Plains during the mid
   to late afternoon, a 50 to 60 knot low-level jet will rapidly
   strengthen. RAP forecast sounding along and near the low-level jet
   during the late afternoon look very favorable for tornadoes, with
   backed surface flow, and long looping hodographs. As the low-level
   jet strengthens, 0-3 km storm-relative helicity is forecast to
   increase to around 400 m2/s2 across much of central and eastern
   Oklahoma into southeast Missouri. The more dominant and supercells
   that interact with the western and northern edge of the low-level
   jet are expected to become tornadic. Several strong tornadoes will
   be likely, and a few long-track EF3+ tornadoes will be possible.

   In addition to the tornado threat, forecast soundings have 700-500
   mb lapse rates near 8 C/km across much of the warm sector this
   afternoon from north Texas to southeast Kansas. This will be
   favorable for very large hail, with hailstones over 2 inches in
   diameter likely with the more intense storms. Later in the evening,
   a line of severe storms is expected to form, moving eastward across
   eastern Oklahoma and north Texas. Wind gusts over 70 mph will be
   possible with the more intense parts of the line. QLCS tornadoes
   will also be possible with rotating cells embedded in the line late
   this evening into the overnight period.

   ...Central Plains/Lower to Mid Missouri Valley...
   An upper-level low will move through the southern Rockies today, as
   the exit region of a mid-level jet overspreads the central Plains.
   At the surface, a warm front will be located from near a surface low
   in southwest Kansas east-northeastward into the mid Missouri Valley.
   This front will be a focus for convective development this
   afternoon. A band of severe storms is expected to form near the
   front and move northward across northern Kansas into southern
   Nebraska during the early to mid afternoon. RAP forecast soundings
   in northeast Kansas near the front from 18Z to 21Z have MLCAPE near
   3000 J/kg, 0-6 km shear around 60 knots, and steep low to mid-level
   lapse rates. This environment will be very favorable for supercells
   with large hail. Hailstones greater than 2 inches in diameter will
   be possible with the more intense storms. In addition, forecast
   soundings have 0-3 km storm-relative helicity in the 250 to 300
   m2/s2 range, suggesting that tornadoes will be likely with the more
   discrete supercells. A few strong tornadoes will be possible.

   Further west into northwest Kansas and eastern Colorado, cold
   temperatures aloft, strong large-scale ascent associated with an
   upper-level low, and strong deep-layer shear will likely support
   lower-topped supercells with large hail and strong wind gusts this
   afternoon.

   ...Mid to Upper Mississippi Valley/Great Lakes...
   An upper-level trough will move northeastward across the Great Lakes
   region today. From near the trough, and southwestward into the mid
   to upper Mississippi Valley, a wide corridor of moderate instability
   will be in place by afternoon. A warm front will be in located along
   the northern edge of the instability, from Iowa northeastward into
   south-central Wisconsin and north-central lower Michigan. As surface
   heating takes place and low-level convergence increases along the
   front, thunderstorms will likely form in the vicinity of the
   boundary. Forecast soundings near the front at 21Z have MLCAPE
   around 3000 J/kg, along with 40 knots of deep-layer shear. This
   should support supercells with potential for large hail and wind
   damage. The severe threat should be greatest during the late
   afternoon and early evening.

   ..Broyles/Thornton.. 04/27/2024

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