SPC AC 151237

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0737 AM CDT Sat Jun 15 2019

   Valid 151300Z - 161200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OK TO WESTERN
   NORTH TX...

   ...SUMMARY...
   Scattered severe thunderstorms are expected across the Midwest and
   Upper Midwest southwest into the southern Great Plains, mainly
   during the late afternoon and evening. The greatest tornado threat
   should be centered on southern portions of Illinois and Indiana. The
   greatest severe wind threat is expected across Oklahoma and western
   north Texas.

   ...Southern Great Plains...
   Primary change is to increase severe wind probabilities for both
   coverage and intensity. 

   A low-amplitude shortwave impulse over western NM will drift east
   into OK through early Sunday. This feature will aid in scattered
   thunderstorm development first in the post-frontal upslope flow
   regime over northeast NM/southeast CO and later along the dryline
   arcing across the TX South Plains and Pecos Valley as surface
   temperatures reach the upper 90s to 103 F west of it. Extremely
   steep mid-level lapse rates around 9.5 C/km (as sampled by 12Z
   Amarillo and Midland soundings) atop mid to upper 60s surface dew
   points will yield a strong to extremely unstable air mass with a
   broad plume of MLCAPE greater than 3000 J/kg. Flow enhancement
   attendant to the shortwave impulse will be modest, with the
   strongest upper flow expected across the Permian Basin to TX South
   Plains region. This suggests outflow-dominated multicells should be
   the predominant mode as convection spreads across OK and western
   north TX, while additional downstream development occurs into
   southern KS near the synoptic front/residual outflow boundary. Large
   hail is possible with initial updrafts, however severe wind gusts
   will probably be the main hazard. The lack of stronger shear may
   limit greater cold pool organization. But the propensity for several
   clusters amid a volatile thermodynamic environment suggest that
   numerous severe wind gusts and isolated significant severe wind
   gusts are possible, mainly this evening. 

   ...Mid-MS to OH Valley...
   Primary change from previous outlook is to increase tornado
   probabilities.

   A pronounced MCV is evident in western MO and is consistently
   progged by guidance to reach OH by evening. An attendant belt of
   strong mid-level westerlies will accompany this wave and in
   conjunction with enhanced low-level southwesterlies, will foster a
   setup conditionally supportive of supercells in the late afternoon.
   Beneath the northeast periphery of the southern Great Plains
   elevated mixed-layer, a pronounced gradient in differential
   boundary-layer heating should develop with residual clouds/early-day
   convection limiting insolation to the north/east. The most likely
   corridor for overlap of enlarged hodographs with at least moderate
   buoyancy should be centered on southern portions of Illinois and
   Indiana. Here, multiple rounds of late afternoon to evening
   thunderstorms will be possible with a risk for all severe hazards,
   including a few tornadoes. 

   ...Upper Midwest...
   Minimal change from previous outlook.

   A low-amplitude shortwave impulse over western ND will drift into
   central MN by early Sunday. Scattered thunderstorms will develop
   southeast of this impulse from the eastern Dakotas into southwest
   Minnesota by late afternoon. While the region will lie north of the
   southern Great Plains elevated mixed layer, a moderately buoyant air
   mass is expected with MLCAPE of 1000-2500 J/kg. Weak flow below 700
   mb will limit low-level updraft organization, but 20-30 kt effective
   shear should support a few multicell clusters and transient
   mid-level rotation as storms spread southeast across IA this
   evening. A mix of isolated to scattered severe wind/hail is
   possible.

   ..Grams/Dial.. 06/15/2019

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