SPC AC 181200

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0700 AM CDT Fri Apr 18 2025

   Valid 181300Z - 191200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE
   SOUTHERN PLAINS INTO THE MID MISSISSIPPI VALLEY AND UPPER GREAT
   LAKES...

   ...SUMMARY...
   Scattered severe thunderstorms are possible from parts of the
   southern Plains northeastward toward the upper Great Lakes, mainly
   from late afternoon into early Saturday morning. Large to very large
   hail and severe wind gusts should be the main hazards, especially
   across the southern Plains where storms will be more concentrated. A
   few tornadoes also appear possible.

   ...Upper Great Lakes to Mid Mississippi Valley...
   Ongoing, mostly elevated thunderstorms aided by persistent low-level
   warm/moist advection and steep mid-level lapse rates should continue
   to pose a large hail and damaging wind threat as they spread quickly
   eastward across southern WI this morning. This activity should
   eventually weaken later this morning as it continues moving across
   Lower MI into a less unstable environment. Behind this initial
   activity, the surface warm sector will attempt to spread northward
   across parts of the Upper Midwest and Great Lakes today, as longwave
   troughing gradually develops eastward over the northern/central
   Plains and Southwest. Given the positive tilt/orientation of this
   upper troughing and enhanced southwesterly flow aloft expected to
   persist through the period, a strong cold front should make only
   slow southeastward progress.

   A cap will likely inhibit surface-based convective development until
   peak afternoon heating and frontal forcing can help lift parcels to
   their LFC. Given nebulous forcing aloft, there is still a fair
   amount of uncertainty regarding overall convective coverage this
   afternoon/evening. Even so, any thunderstorms that can develop along
   or ahead of the front could pose a threat for severe hail and
   damaging winds, with strong deep-layer shear aiding updraft
   organization. This severe threat may persist for much of the
   evening, and perhaps continuing into the early overnight hours.

   ...Southern Plains to the Ozarks...
   The southern portion of the cold front is forecast to decelerate and
   eventually stall over parts of OK later today. A dryline will extend
   southward from a weak frontal low across northwest to west-central
   TX by late afternoon. Even with widespread mid/high-level cloudiness
   present, robust daytime heating of the moist warm sector is
   anticipated across the southern Plains today. The low-level cap
   should eventually be breached by late afternoon/early evening
   (around 22-00Z), particularly along/near the cold front, and perhaps
   the front/dryline intersection as well. Strong southwesterly flow
   aloft and related deep-layer shear will likely support organized
   severe convection.

   Initial supercell development should pose a threat for large to very
   large hail, potentially up to 2-3 inches in diameter. With time,
   upscale growth into multiple clusters/short line segments is
   expected through the evening into early Saturday morning, as a
   south-southwesterly low-level jet gradually strengthens. An increase
   in the severe/damaging wind threat is anticipated as this mode
   transition occurs. The threat for a few tornadoes remains apparent,
   especially across parts of OK along/south of the front, as favorable
   low-level shear will be present this evening where supercells may
   still exist. Even with a higher concentration of thunderstorms
   expected across the southern Plains, the messy convective mode this
   evening and tendency for convection to be undercut by the cold front
   currently limit confidence in delineating a corridor of greater
   severe hail/wind potential.

   ..Gleason/Broyles.. 04/18/2025

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