SPC AC 170551

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1251 AM CDT Sun May 17 2020

   Valid 171200Z - 181200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
   ILLINOIS INTO CENTRAL INDIANA...INCLUDING NORTHWEST KENTUCKY...

   ...SUMMARY...
   A few weak tornadoes are possible today across parts of Illinois,
   Indiana and western Kentucky. Scattered storms, some with hail and
   strong wind gusts, are likely from Oregon into northwest Montana
   this afternoon. Other strong storms are possible over Ohio, and into
   western Tennessee and Mississippi during the day.

   ...Midwest/OH Valley region...
   A compact upper low will move southeast across IA during the day and
   into IL overnight, enhancing lift and increasing shear with 40 kt
   midlevel southwesterlies and cooling aloft. Low pressure will move
   very slowly east across northern IL, with a cold front extending
   from central IL southward along the MS River by 00Z. Ahead of the
   cold front, a long fetch of moisture will exist from the lower MS
   Valley northward into IL, with mid to upper 60s dewpoints common
   beneath 30-40 kt southerly 850 mb winds. Farther north, a warm front
   will slow its progression along a line from Chicago to Cleveland.

   Scattered showers and storms are likely to be ongoing early in the
   day, both in the warm advection zone and along the cold front from
   western IL into MO. Gradual destabilization will occur east of the
   front, and storms should solidify during the afternoon and evening
   as stronger convergence interacts with the unstable air mass.
   Veering winds with height will favor rotating storms, and a few may
   produce brief tornadoes. This threat may persist well into the
   evening as the low-level jet remains favorable.

   Farther south into western TN and northern MS, lift will not be as
   focused, but a moist air mass and sufficient convergence within the
   surface trough will favor isolated afternoon storms. Weakly veering
   winds with height may support a few stronger cells capable mainly of
   strong wind gusts, though weak rotation cannot be ruled out beneath
   25-30 kt 850 mb flow.

   Daytime storms are also likely to form over northern OH around 18Z
   as the warm front lifts north. Here, SBCAPE may approach 1000 J/kg,
   with weakly veering winds with height possibly supporting a
   brief/weak tornado as well.

   ...Eastern OR and WA into ID and northwest MT...
   A broad area of strong southwest winds aloft will overspread much of
   the west with an upper trough just offshore. During the day, a
   surface trough will extend from northern NV into Alberta, with winds
   shifting to westerly over central WA and OR. Daytime heating with
   cooling temperatures aloft will result in a few hundred J/kg MLCAPE,
   with strong deep-layer shear across the region. Scattered strong
   storms will form after 18Z over central and northeast OR and rapidly
   move northeast producing localized severe wind or hail.

   ..Jewell/Moore.. 05/17/2020

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