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   ACUS01 KWNS 182002   
   SWODY1   
   SPC AC 182000   
      
   Day 1 Convective Outlook   
   NWS Storm Prediction Center Norman OK   
   0200 PM CST Tue Nov 18 2025   
      
   Valid 182000Z - 191200Z   
      
   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF   
   THE LOWER OHIO VALLEY AND MIDDLE MISSISSIPPI VALLEY...   
      
   ...SUMMARY...   
   Widely scattered severe storms are possible across parts of the   
   middle Mississippi Valley and lower Ohio Valley this afternoon and   
   evening.   
      
   ...20Z Update...   
   The primary change with this update was the addition of a Slight   
   Risk (2/5) over parts of the Lower OH Valley and Mid MS Valley --   
   driven by 15-percent hail probabilities. The latest visible   
   satellite imagery shows an increasingly agitated boundary-layer   
   cumulus field evolving across southeast MO -- in the vicinity of a   
   frontal wave/weak surface low. Continued heating amid increasing   
   boundary-layer moisture ahead of this feature should erode   
   inhibition through the remainder of the afternoon and support   
   isolated to widely scattered thunderstorms along a pre-frontal   
   surface trough. Any storms that form will be moving into an   
   environment characterized by around 50 kt of effective shear and   
   weak-moderate surface-based buoyancy. This will conditionally favor   
   discrete/semi-discrete supercells capable of producing large hail   
   and locally strong gusts. While less certain, a couple of tornadoes   
   cannot be ruled out if established supercells evolve, given   
   sufficient low-level hodograph curvature. Elsewhere, the Marginal   
   Risk was expanded slightly northward to account for an ongoing   
   elevated hail risk.   
      
   ..Weinman.. 11/18/2025   
      
   .PREV DISCUSSION... /ISSUED 1030 AM CST Tue Nov 18 2025/   
      
   ...Middle Mississippi Valley/Lower Ohio Valley...   
   Clusters and northeast/southwest-oriented bands of elevated   
   thunderstorms persist at late morning either side of the Ohio River,   
   spanning southeast Indiana into northern/western Kentucky including   
   near the confluence of the Ohio and Mississippi Rivers. This   
   convection will result in some additional net south/southwestward   
   forecast focus of the warm sector later today, even while fairly   
   aggressive warm-sector moistening is occurring across the Ozarks as   
   surface dewpoints climb through the lower/some middle 60s F.   
      
   A shortwave trough/moderately strong jetlet over Iowa and northern   
   Missouri this morning will continue to gradually minor/open while   
   moving east-southeastward toward the middle Ohio Valley by tonight.   
   Given the trend of this system, the related surface low will   
   gradually weaken while air mass modification/convective recovery   
   occurs with a northeastward-expanding warm sector toward the lower   
   Ohio Valley.   
      
   Current expectations are for some re-intensification of convection   
   to occur this afternoon across far southeast Missouri, southern   
   Illinois and western Kentucky, although some of these   
   developmental/environmental details depend on the disposition of   
   still-recurring convection near/south of the Ohio River. There is   
   still some sub-regional uncertainty with how far north the surface   
   warm sector will be able to advance, and daytime heating may be   
   muted by persistent cloudiness. But, the best combination of weak to   
   locally moderate instability and favorable deep-layer shear will   
   generally overlap across the aforementioned region this afternoon   
   and evening as a 50-60+ kt westerly mid-level jet moves overhead.   
      
   Any sustained supercell may be capable of producing severe hail   
   along with locally damaging winds, with elevated convection possible   
   north of the warm front into south-central Illinois/southern   
   Indiana. Some threat for a tornado or two may also exist if   
   sufficient boundary-layer instability can advance far enough   
   northward in tandem with the warm front and enhanced low-level shear   
   to support surface-based thunderstorms.   
      
   A narrow zone centered on far southeast Missouri, far southern   
   Illinois, western Kentucky and northwest Tennessee will continue to   
   be closely monitored and reevaluated for an upgrade (20z D1 update)   
   should confidence in surface-based storms increase near the surface   
   low/warm front late this afternoon and early evening.   
      
   ...Lower Colorado River Valley/Arizona...   
   A closed mid/upper-level low along the coast of central/southern   
   California will make only slow progress southward today. Large-scale   
   ascent associated with a south-southwesterly mid-level jet should   
   encourage additional convective development today across parts of   
   the lower Colorado River Valley and Arizona. While deep-layer shear   
   appears adequate for organized updrafts, weak instability will   
   likely limit the overall severe threat across this region, although   
   small hail/gusty winds a few stronger storms could occur this   
   afternoon.   
      
   $$   
      
   = = =   
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