SPC AC 040744

   Day 3 Convective Outlook CORR 1
   NWS Storm Prediction Center Norman OK
   0244 AM CDT Thu Jun 04 2020

   Valid 061200Z - 071200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   WESTERN AND CENTRAL SOUTH DAKOTA...

   CORRECTED FOR WORDING

   ...SUMMARY...
   Severe thunderstorms capable of producing large hail, damaging wind
   gusts and a tornado threat will be possible in parts of the northern
   Plains Saturday afternoon and evening.

   ...Northern Plains...
   An upper-level ridge will amplify and move quickly northeastward
   across the northern Plains on Saturday. At the surface, a low will
   deepen in the northern Montana as a warm front moves northward into
   the northern Plains. Along and south of the warm front, a moist
   airmass will be in place across much of South Dakota. A narrow
   corridor of maximized low-level moisture will exist across eastern
   and northern Montana. Strong instability is forecast to develop to
   the south of the warm front Saturday afternoon across parts of
   southern and western South Dakota with moderate instability further
   northwestward along the moist axis. Large-scale ascent will increase
   across the northern Plains during the day as a shortwave trough
   approaches from the southwest. Although a capping inversion is
   forecast to be in place across much of the instability corridor, the
   cap should weaken by late afternoon. This combined with increasing
   large-scale ascent and low-level convergence along the warm front
   should result in surface-based convective initiation across the
   instability corridor Saturday afternoon from southern and western
   South Dakota into central and eastern Montana. Other thunderstorms
   may develop further to the northeast in the cooler airmass across
   northeastern South Dakota and southern North Dakota. Thunderstorms
   are expected to grow upscale and move northeastward across the
   northern Plains from late Saturday afternoon through the evening.

   Forecast soundings along the instability axis by 22Z on Saturday to
   the east of Rapid City, South Dakota show moderate to strong
   instability with MLCAPE in the 2500 to 4500 J/kg range, lower or
   higher depending upon which model solution you look at. The wind
   profile shows directional shear from the surface to 700 mb with
   strong speed shear in the mid-levels. The wind profile will likely
   support supercell development. 700-500 mb lapse rates of 7.5 C/km
   will be favorable for large hail with the more intense cores. The
   large hail threat along with a possibility of hailstones greater
   than 2 inches in diameter, is forecast to be greatest across western
   and central South Dakota along the corridor with the strongest
   instability. Large hail will also be possible in central and
   northern Montana but weaker instability there may keep the threat a
   bit more isolated. A few tornadoes may occur as supercells mature
   and move northeastward into strengthening low-level flow during the
   late afternoon and early evening. The wind damage threat will be
   maximized with the stronger supercells. This wind damage threat
   should become greater during the early to mid evening, especially if
   a transition to linear mode occurs.

   ..Broyles.. 06/04/2020

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   NOTE: THE NEXT DAY 3 OUTLOOK IS SCHEDULED BY 0730Z