SPC AC 220111

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0811 PM CDT Tue May 21 2024

   Valid 220100Z - 221200Z

   ...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   WISCONSIN AND ILLINOIS...

   ...SUMMARY...
   An outbreak of severe thunderstorms will continue this evening
   across parts of far eastern Iowa, eastern Missouri, northern
   Illinois and Wisconsin. A potential will exist for strong tornadoes
   and widespread damaging winds. The severe threat will also continue
   south-southwestward into the Ozarks and southern Plains, with a
   threat for isolated large hail, wind damage and a tornado or two.

   ...Mid To Upper Mississippi Valley/Western Great Lakes...
   The latest mosaic radar imagery shows scattered severe thunderstorms
   located from southern Wisconsin southward across far eastern Iowa,
   western Illinois into eastern and southern Missouri. The storms are
   located from a warm front in Wisconsin and extend southward into the
   mid Mississippi Valley along and near a pre-frontal trough. MLCAPE
   along this corridor is estimated by the RAP in the 2000 to 3000 J/kg
   range. On water vapor imagery, a shortwave trough, and an associated
   70 to 90 knot mid-level jet is moving through southeast Iowa. This
   feature is enhancing large-scale ascent and deep-layer shear across
   much of the mid to upper Mississippi Valley. In addition, a 40 to 60
   knot low-level jet is analyzed by the RAP over the mid to upper
   Mississippi Valley. As low-level flow continues to increase this
   evening, severe thunderstorm development will likely be maintained
   for several more hours.

   The 00Z sounding from Davenport, IA has MLCAPE near 2000 J/kg, with
   0-6 km shear 50 to 55 knots and 0-3 km storm-relative helicity near
   300 m2/s2. This appears to be representative of the environment
   further to the east, where much of the severe convection is ongoing.
   This will support supercells with tornadoes, wind damage and
   isolated large hail. The low-level shear will support a potential
   for strong tornadoes. The greatest threat for strong tornadoes will
   be near and to the east of the low-level jet from southern Wisconsin
   into northern Illinois. The greatest potential for wind damage will
   be along and ahead of organized line segments. Wind speeds of 70 to
   80 mph will be possible with the more intense bowing line segments.
   Tornadoes may occur with rotating cells embedded in the line.
   Hailstones of greater than 2 inches in diameter will be possible
   with the more dominant supercell storms. The severe threat should
   become more isolated after midnight as instability decreases across
   the mid to upper Mississippi Valley.

   ...Ozarks/Southern Plains...
   Widely scattered strong to severe storms are ongoing across the
   Ozarks and in parts of the southern Plains, where the RAP is
   analyzing strong instability. To the east of a dryline, MLCAPE is
   estimated in the 3000 to 4000 J/kg range from eastern Oklahoma
   southward across much of the eastern half of Texas. Across the
   airmass to the east of the dryline, surface dewpoints are in the 70s
   F. In addition, the RAP has moderate to strong deep-layer shear
   analyzed across most of the moist airmass. The 00Z sounding at
   Little Rock, AR and Shreveport, LA have 0-6 km shear in the 50 to 60
   knot range with 700-500 mb lapse rates in the 7.5 to 8 C/km range.
   This environment will be favorable for supercells with large hail.
   Hailstones greater than 2 inches in diameter will be possible with
   the more dominant supercells. Wind damage will also be likely with
   supercells, and or bowing line segments. The severe threat is
   expected to continue this evening, but should become more isolated
   toward midnight.

   ..Broyles.. 05/22/2024

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